Textbook of Rabbit Medicine, Notas de estudo de Medicina Veterinária

Baixe Textbook of Rabbit Medicine e outras Notas de estudo em PDF para Medicina Veterinária, somente na Docsity! Butterworth–Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 2002 © Reed Educational and Professional Publishing Ltd 2002 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 0LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data Harcourt-Brown, Frances Textbook of rabbit medicine 1. Pet medicine 2. Rabbits – Diseases 3. Rabbits I. Title II. Harcourt-Brown, Nigel H. 636.9'322'0896 ISBN 0 7506 4002 2 Composition by Scribe Design, Gillingham, Kent, UK Printed and bound in Great Britain by Alden Press, Oxford For information on other veterinary publications visit our website at www.bh.com/veterinary The publishers and author would like to acknowledge the support of Burgess Supafeeds in the production of this book. Acknowledgements for reading through the text, correcting mistakes and for their continued interest in rabbit related topics. I am grateful to the nurses and other members of our practice who have endured my obsession with rabbits and have helped me to treat and nurse these patients with dedication and commitment. Our four children deserve thanks for their forbearance during my preoccupation with rabbit diseases over the last few years. Lastly, and most importantly, I would like to thank my husband Nigel who has helped and encouraged me throughout every stage. He has been my mentor, scrutineer and anatom- ical illustrator as well as housekeeper, cook and professional partner. Frances Harcourt-Brown x Preface Plate 1. Identification ring occluding the blood supply to the hind foot. Pedigree rabbits are identified by aluminium rings slipped over the hock when the rabbit is 8–10 weeks old. The rings are supplied by the British Rabbit Council in a range of sizes. Each ring has the year of birth and a unique number from which the rabbit can be identified. Occasionally, rabbits with identification rings are sold as pets. It is advisable to remove the rings because hair can become entrapped beneath the ring and occlude the blood supply to the foot. This rabbit was euthanased. Plate 2. Anisocytosis and poly- chromasia. The red blood cells of rabbits vary in diameter within a range of 5.0–7.8 µm. This variation in diameter (anisocytosis) is a feature of blood smears from rabbits and is not a significant finding. There is also variation in erythrocyte colour (polychromasia) in normal rabbits. The blood smear illustrated was from a normal rabbit and was stained with Rapi-diff. Inter- pretation of haematology results is discussed in Section 6.2.2. (Photograph taken by Dr Joan Duncan, Idexx Laborato- ries, Wetherby.) Plate 3. Patchy hair loss. Some breeds of rabbit with fluffy coats, notably Dwarf lops and Minilops, develop hairless patches of skin during moulting. The alopecic areas often cause concern to owners. The bald skin is not inflamed. A typical lesion is illus- trated. Regrowth of hair is rapid. Dense fur starts to grow at the centre of the lesion within 7–10 days and takes place simultane- ously with hair loss at the periphery of the lesion. This is a self-limiting physiological process. Plate 6. Ulcerative pododermatitis in a Rex rabbit. Pressure sores develop in the thin skin over the bony prominence of the central tarsal bone, especially in rabbits with sparse hair coating such as the Rex. This plate shows the hock of a 4-year-old neutered male Rex house rabbit. The hairless area of reddened skin that does not blanch on pressure is an early sign of ulcer- ative pododermatitis. Once the area has lost its protective fur, the skin is subject to increased mechanical trauma and pressure. The lesions can progress to form decubital skin ulcers. Occasionally the medial plantar vein or artery, which lie just beneath skin, is eroded and causes haemorrhage. Plate 4. Ear mites (Psoroptes cuniculi). Otitis externa caused by ear mites (Psoroptes cuniculi) in rabbits is characterized by a crusty exudate within the external ear canal, which often extends up the pinna. Occasionally, only one ear is affected. The condition is intensely pruritic and painful. A typically affected ear is illustrated. The skin beneath the exudate is ulcerated and sore. The condition responds well to treatment with ivermectin or selamectin. Cleaning the ear is painful for the rabbit and unnecessary. Further discussion of Psoroptes cuniculi infestation can be found in Section 9.14.2.1.The mite is illustrated in Figure 16.1. Plate 5. Initial stage of ulcerative pododermatitis. The area of skin on the point of the hock of rabbits is prone to pressure necrosis. A small area of hairless skin can often be found in adult pet rabbits although it is usually concealed by the fur that lies across it. Hard flooring, lack of exercise and long periods of inactivity increase the pressure over the hock. Plate 5 shows a circular patch of hairless skin on the hock of a rabbit that was presented for vaccination. It was an incidental finding. Plate 15. Auriscopic view of normal cheek teeth. The cheek teeth can be examined using an auriscope (otoscope). Auriscopic examination gives a guide to the condition of the cheek teeth. General anaes- thesia is required for a thorough examina- tion. This plate is a view of the cheek teeth of a conscious healthy 3-year-old female rabbit taken through a rigid endoscope. The normal zigzag pattern of the points on the lingual edge of the occlusal surface on the lower cheek teeth can be seen. Most rabbits tolerate the auriscopic examination of the oral cavity well, unless there is a painful lesion within the mouth. Plate 14. Healthy mandible to show points on the cheek teeth. A prepared mandible from a wild rabbit. Sharp points on the lingual edge of the lower cheek teeth is a normal finding. They do not require removal. Plate 13. Wild rabbit skull: ventrodorsal view. A ventrodorsal view of the same skull as in Plate 12. These views can be used to identify radiographic landmarks illustrated in Figures 7.9–7.11. Plate 16. Prepared skull of a rabbit with advanced dental disease; lateral view. This is a skull of a 4-year-old Nether- land Dwarf female rabbit that was presented for euthanasia. She had spent her entire life confined to a hutch and was fed on ad lib ‘rabbit food’ consisting of a mixture of maize, peas, wheat, oats, pellets and extru- sions. Hay was available although she didn't eat it. No vegetables were offered because the owner believed they would cause ‘diarrhoea’. She was suffering from dacryo- cystitis and inappetance. The skull shows generalized osteopaenia. The roots of all the teeth are elongated and penetrating periosteal bone. Calcification around the roots has resulted in large bony reactions that are effectively welding the teeth into the skull. There is a large bony reaction in the orbit around the site of the lacrimal sac and nasolacrimal duct. The crowns of most of the teeth have broken off. Plate 18. Mandible from a rabbit showing early signs of dental disease. This mandible is from a 2-year-old castrated Dwarf Lop house rabbit that died due to intestinal obstruction caused by a felt of ingested hair. Although swellings could be palpated along the ventral border of the mandible, no other signs of dental disease were evident. The crowns were not long. The structure, shape and position of the teeth has changed so they are no longer in alignment. Loss of alveolar bone has resulted in wide periodontal spaces. The second right premolar is starting to tip towards the tongue. Plate 17. Prepared skull of a rabbit with advanced dental disease; ventrodorsal view. A ventrodorsal view of a prepared skull of a 4-year-old male Dwarf lop rabbit. He was kept in a hutch for most of the year but was placed in a run in the garden on fine days during the summer months. The rabbit was always a finicky eater, he would (or could) not eat hay or hard vegetables. He lived on bread and selected ingredients from mixed rabbit food. He would eat watercress and the occasional dandelion leaf. During his life, the rabbit had suffered from a range of clinical condi- tions related to his teeth: epiphora, dacro- cystitis, molar malocclusion and incisor malocclusion. The progression of dental disease is summarized in Box 7.1. The rabbit was euthanased because he became dyspnoeic. The skull shows osteopaenic bone and dilation of the maxillae. Abscesses have developed at the roots of the primary incisors, which are occluding the nasal passages. The crowns of the cheek teeth have disintegrated. Plate 21. Spurs on the upper premo- lars. Sharp spurs had developed on the upper premolars of this mature mixed breed male rabbit. He was adopted from a rescue centre 1week before this photograph was taken. He had spent 6 months in the rescue centre and had been passed as ‘fit for rehoming’. The rabbit was able to eat but was not grooming well and was thin. The spur had penetrated the buccal mucosa inside the cheek and an abscess was begin- ning to form. The crowns look dull and discoloured. There is erosion of the gum around the first premolar resulting in a cavity that could entrap food material. These spurs were easily trimmed off using molar clippers. A dental burr was not used because of the risk of soft tissue damage. Plate 20. Spur on lower cheek tooth. A sharp spur has developed on a lower cheek tooth of this 2-year-old male Dwarf lop rabbit. The spur has lacerated the tongue. The rabbit was not grooming. He had cheyletiellosis and there were caecotrophs caked to the fur under the tail. He was salivating and unable to eat. The spur was trimmed using a set of long handled molar clippers. The rest of the teeth were checked and trimmed or smoothed with a diamond rasp where necessary. He was given a non- steroidal analgesic. The rabbit started to eat as soon as he regained consciousness. Two months later, he was presented because a spur had developed on a different cheek tooth. The spur on the tooth illustrated had not regrown. Trimming cheek teeth is described in Section 7.10.2. (Image repro- duced with kind permission from Waltham Focus.) Plate 19. Comparison of the structure of healthy and maloccluded cheek teeth. This plate shows an upper and lower premolar taken from the skull of a healthy rabbit (left) and a rabbit suffering from molar malocclusion (right). The maloccluded teeth are curved and elongated. The enamel is poor. Curvature of the teeth has altered the direction of the biting force on the teeth. The changes in tooth shape are irreversible and show that it is impossible to restore normal occlusion by corrective dentistry. Plate 28. Pneumonia. This plate shows the lungs of a juvenile mixed breed male rabbit that was found dead after not eating for 24 h. The lungs showed evidence of acute pneumonia typical of Pasteurella multocida infection. Plate 30. Cardiomyopathy. This plate shows the heart of an adult neutered male French lop (> 6 kg) that died suddenly following a period of lethargy but no other obvious clinical signs. Histopathological and gross post-mortem examination showed no lesions in other organs apart from congestion. Sections of heart muscle showed myocardial fibrosis. Plate 29. Nasal foreign body. This plate shows the nostrils of a mature Dwarf lop male rabbit that was presented because he was sneezing. In this case, a blade of hay could clearly be seen protrud- ing from the nostril and the foreign body was easy to remove. Seeds and stems of hay can make their way into a number of sites and cause disease in rabbits. Nasal foreign bodies are relatively common. Sometimes stems of hay can lodge in or around the larynx and cause choking. Foreign bodies can become wedged in the periodontal space. Both these conditions are linked with dental disease. Grass seeds can also lodge in the inguinal skin folds that are situated on either side of the genital orifice. Plate 33. Urine scalding. Any condition that prevents a rabbit from adopting the correct stance for urination can result in urine retention or urine scalding of the perineal skin. Once the skin is inflamed, urethritis makes urination painful and a vicious circle begins (see Figure 14.2). The rabbit illustrated is a 3-year-old neutered male Dwarf lop house rabbit that was suffering from urine scalding of the perineum and inner thighs. He had urine retention and ‘sludgy urine’ (see Figure 14.1). Radiography revealed a displaced 7th lumbar vertebra and a narrowed lumbosacral disc space. As a result of the spinal lesion, the rabbit could not adopt the correct position to urinate. Plate 34 shows the urine from this rabbit. Plate 32. Normal urination stance. Rabbits that are given the freedom to exercise and mark their territory urinate frequently. In order to direct the jet of urine away from the body, the rabbit lifts its hindquarters and raises its tail. Failure to adopt the correct stance for urination can result in urine contaminating the fur around the genitalia and scalding the skin. Plate 31. Kidney showing gross lesions associated with Encephalitozoon cuniculi infection. This plate shows the kidney of a 4-year-old male Dwarf lop rabbit that was known to be seropositive for Encephalitozoon cuniculi although he showed no obvious clinical symptoms. Both kidneys showed irregular, depressed areas. E. cuniculi causes granulomatous interstitial nephritis. Long-standing lesions show inter- stitial fibrosis and collapse of the parenchyma. Early lesions show focal granulomatous inflammation. Lesions are present in the renal tubule and spores are shed in the urine, which is infective to other rabbits. Plate 34. A comparison of normal urine with ‘sludgy’ urine. There are differences in the way in which sediment forms in sludgy and normal urine. The two samples on the left of the picture are ‘sludgy’ urine that was expressed from the rabbit illus- trated in Plate 33 and Figure 14.1. The far left sample was the urine that was initially expressed from the bladder. The middle sample was thick viscid urine that had apparently been retained in the bladder for some time. It had the consistency of tooth- paste. A fine sediment that set like concrete formed in both these samples after they were left standing for a few hours. The sediment could only be broken up by shaking the sample vigorously. The sample on the right is urine from a normal rabbit that also contains sediment. However, the sediment in the normal sample easily forms a suspension with gentle shaking, even after it is left undisturbed for 48 h or more. Analy- sis of both samples is similar. They both contain calcium carbonate and some calcium oxalate crystals which give urine its radio- dense appearance on radiographs. Plate 36. Cysticercus pisiformis. Cysticercus pisiformis is the larval stage of Taenia pisiformis, which is a tapeworm that affects dogs and foxes with rabbits acting as the intermediate host. Multiple oval cysts are found in the mesentery. The cysts contain the inverted scolex of the tapeworm. This plate shows some of the cysts that were found during an exploratory laparotomy of an anorexic rabbit that was showing signs of abdominal discomfort. No faeces had been passed for 48 h. The rabbit was a mature Angora male that had recently been adopted by a rescue centre. The cysts were most abundant in the mesentery between the stomach and the distal colon. The cysts had become so large that they had obstructed the large intestine. Plate 35. The liver of a rabbit that had died from viral haemorrhagic disease (VHD). The typical appearance of the liver of a rabbit that has died from viral haemor- rhagic disease is shown. The liver is enlarged, although not strikingly so, and friable and pale with a distinct lobular pattern. The liver is always affected in cases of viral haemorrhagic disease although the gross appearance may not reflect the severe histopathological changes. The histological appearance of the liver is often diagnostic. It is severely congested with marked hepato- cyte necrosis involving extensive areas of most lobules. Follicle stimulating hormone (FSH) stimulates ovarian follicles to develop and produce oestrogens that cause the female to be recep- tive. Follicular development occurs in waves with five to 10 follicles on each ovary being at the same stage of development at any one time. When the follicles reach maturity they produce oestrogen for about 12–14 days. If ovulation has not occurred during this period, the follicles degenerate with a corre- sponding reduction in oestrogen level and sexual receptivity. After about 4 days a new wave of follicles begins to produce oestrogen and the doe becomes receptive again. Many factors influence this cyclic rhythm including nutrition, light, temperature, sexual stimula- tion and individual variation. In general, the receptive period lasts 14–16 days with a period of non-receptivity for 1–2 days (Patton, 1994). Mating stimulates ovulation approximately 10 hours post coitus (Harkness, 1987). Ovulation can also be induced by proximity of an entire male, mechanical stimulation of the vagina or by the act of being mounted by another female. Gestation is maintained by progesterone that is produced exclusively by the ovarian corpora lutea. In the absence of fetuses, pseudopregnancy can occur after ovulation and is maintained by corpora lutea that degrade after approximately 17 days (Fekete and Huszenicza, 1993). In the wild, unfavourable winter conditions or lack of food suppress follicular activity. Does can be mated soon after giving birth and may be lactating and pregnant at the same time. Litter sizes vary and larger breeds generally have larger litters (Sandford, 1996). Average litter size is five to eight, the length of gesta- tion is 30–32 days so it is possible for a doe to have six litters in a year and produce 40–50 offspring. The nest is made out of hay or other bedding material and lined with fur plucked from the doe’s abdomen and flanks. Parturition usually takes place in the morning and is completed in less than half an hour although, occasionally, young can be born hours or even days apart (Adams, 1987). The young are born bald, blind and helpless. Most passive immunity is obtained before birth, although some antibodies are present in the colostrum (Brewer and Cruise, 1994). In the wild, newly born rabbits or ‘kits’ are cleaned and nursed by the doe before she leaves the nest and blocks the entrance. She will stay in the vicinity of the nest but only returns once or twice daily to feed the kits for a period of 3–5 minutes during which time a baby rabbit can drink 20% of its bodyweight (Donnelly, 1997). Rabbit milk is concentrated, containing 13–15% protein, 10–12% fat and 2% carbohy- drate. The young rabbits emerge from the nest at about 18 days, start nibbling grass or hay at 3 weeks and are weaned at about 25 days of age. 1.5 Digestive physiology The alimentary tract of the rabbit is adapted for the digestion of large quantities of fibrous food (Figure 1.1). Rabbits are hindgut fermenters and rely on microbial fermenta- tion of food within the caecum to provide nutrients. In the stomach and small intestine, digestion and absorption of nutrients is similar to monogastric mammals. The end- products of the digestive processes are separated in the colon into indigestible mater- ial and substances that can be metabolized by caecal microorganisms. Separation of the ingesta depends on particle size. The proxi- mal colon of the rabbit is specially adapted for the separation of large particles of 3Biological characteristics Key points 1.1 • Domestic rabbits are descended from the European rabbit, Oryctolagus cuniculus and retain many behavioural characteristics of their wild ancestors • Wild rabbits live in groups of 6–8 with a well defined social hierarchy. Males fight for dominance and females aggressively defend their nesting site • Wild rabbits seldom become tame in captivity even if they are hand-reared • Rabbits are induced ovulators without a defined oestrus cycle. Females show a cyclic rhythm of sexual receptivity • Pseudopregnancy is the result of ovula- tion without fertilization. Ovulation can be stimulated in the absence of mating by the close proximity of a male, mechanical stimulation or mounting by another female • Lactating does remain in the vicinity of their nest and defend it but only return once or twice daily to suckle the young. 4 Textbook of Rabbit Medicine Parotid salivary gland Mandibular salivary gland Oesophagus Stomach [15% GIT volume] Cardia Spleen Left lobe of pancreas Jejunum Mesentery Accessory pancreatic duct Ileum Taenia Haustra Taenia Haustrum (a) Ileocaecocolic complex Mesentery Warzen Descending duodenum Pancreas Distal colon Body of caecum IleumAppendix Proximal colon Base of caecum Ampulla caecalis coli Sacculus rotundus(a)Anus Rectum Descending colon Transverse colon Ascending colon Distal colon [80—100 cms] No haustra Fusus coli [4 cms] No haustra Proximal colon [20 cms] 1 Taenia; 1 Haustrum Proximal colon [10 cms] 3 Taeniae; 3 Haustra Ampulla caecalis coli Sacculus rotundus Caecum [60% GIT volume] [40 cms] Vermiform caecal appendix Sublingual salivary gland Buccal salivary gland Pylorus Bile duct Ampulla Descending duodenum Ascending duodenum Right lobe of pancreas Transverse duodenum Ileocolic valve Figure 1.1. 5Biological characteristics Figure 1.1. Schematic diagram of the anatomy of the alimentary tract of the rabbit. The alimentary tract of the rabbit is adapted for the digestion of large quantities of fibrous food. The teeth continually grow and wear against each other to maintain their shape. The incisors are worn to a fine cutting edge that can be used to slice through vegetation or gnaw hard substances such as bark or wood. The occlusal surfaces of the cheek teeth are worn to an effective grinding surface that is used to reduce food particles to a small enough size to be swallowed. There are a number of well-developed salivary glands. The cardia and pyloric sphincter are muscular and well-developed. The relatively voluminous stomach is simple in type and always contains food. The stomach contents comprise approximately 15% of the contents of the gastrointestinal tract. The duodenum forms a loop with descending, transverse and ascending parts. It has an extensive mesentery. The duodenum begins with a slight enlargement approximately 1 cm from the pylorus that receives the bile duct. The right lobe of the pancreas is widely dispersed in the mesoduodenum as many isolated lobules. The main body and left lobe of the pancreas run in the mesentery that attaches the transverse colon to the stomach and spleen (see Figure 10.4). A single accessory pancreatic duct opens into the junction between the descending and transverse duodenum. The jejunum is long, convoluted and relatively free of attachments. It occupies the dorsal half of the left flank and the caudal half of the abdomen (see Figures 3.3–3.5). The ileum is closely associated with the mesentery that connects part of the ascending colon to the caecum to form the ileocaecocolic complex (see 1.1a). The end of the ileum is expanded into a thick walled sacculus rotundus. The caecum and appendix are shown as a straight tube, but are in fact a coiled spiral (see 1.1a). The thin-walled caecum is a large organ that ends in an appendix that is heavily endowed with lymphoid tissue. The ascending colon of the rabbit can be divided into four sections. The first section is approximately 10 cm long and has three longitudinal flat bands of muscular tissue or taeniae that separate rows of haustra or sacculations. Small protrusions, ‘warzen’ (warts), approximately 0.5 mm in diameter, can be seen on the mucosa in this section of colon. The second section of ascending colon is approximately 20 cm in length and has a single taenia and fewer, smaller haustra. The third portion of the ascending colon is termed the fusus coli and is a muscular area about 4 cm long. The fusus coli opens into the fourth section of ascending colon that is histologically indistinguishable from the transverse and descending colon. Because the fusus coli forms such a natural division between two morphologically and functionally distinct sections of the rabbit colon, the terms ‘proximal’ and ‘distal’ colon are sometimes used instead of ascending, transverse and descending colon (Snipes et al., 1982). The proximal colon includes the three taeniae section, the single taenia section and the fusus coli. The distal colon is 80–100 cm long and runs from the fusus coli to the rectum. 1.1a Ileocaecocolic complex. (Figure shows a ventral view of the ileocaecocolic complex, which occupies more than half of abdomen, mainly on the right side (see Figures 3.3–3.5)). The complex has been slightly unrolled in order to illustrate its component parts. There are mesenteric attachments between the caecum, appendix, proximal colon, ileum, distal colon and descending duodenum. These organs form a complex three-dimensional structure in rabbits. The term ‘ileocaecocolic complex’ is used to describe the structure in this text. The body of the caecum has a spiral form consisting of one and a half turns, ending in an appendix that extends to the right flank. The axis of the spiral is the base of the caecum that receives the end of the ileum in the form of the sacculus rotundus. The ileum lies between the concavity of the body of the caecum and the convexity of the upper ascending colon and is attached to these two structures by peritoneal folds. Because of their peritoneal attachments to the spiral caecum, the ileum and upper ascending colon are also arranged in a spiral, and are integral components of the ileocaecocolic complex. The upper ascending colon begins as a smooth oval dilation, the ampulla coli, that forms the junction with the sacculus rotundus and the caecum. Parts of the descending colon and descending duodenum are attached to the distal end of the caecum by peritoneal folds. The left lobe of the pancreas lies in the peritoneal fold between the descending duodenum and descending colon. 8 Textbook of Rabbit Medicine Volatile Fatty Acids: VFA Acetic Acid 60—70% Butyric Acid 15—20% Propionic Acid 10—15% Water Water Water Water VFA Monosaccharides Water Water Caecotrophs contain amylase & lysozyme pH 3 during their digestion Food Water pH 1—2 Electrolytes Water VFA VFA VFA HCO3 — HCO3 H+Cl— Continuous saliva secretion K+ HCO3 — and amylase Vitamins Microbial amino acids Lactic acid Amino acids Lipids Increased haustral activity High frequency 3 second duration contractions Segmental low frequency 14 second duration contractions Monophasic progressive peristaltic wave 5 seconds duration Autonomic nerves Aldosterone Prostaglandin Digestible fibre Indigestible fibre Strong contractions Electrolytes peristalsis & caecal contraction Ileocolic valve closed Lysozyme peristalsis haustral activity Gentle contractions mucus secretion Monophasic peristaltic contractions 1.5 seconds duration Caecotrophs are passed 1.5—2.5 times faster than faeces Autonomic nerves Aldosterone Prostaglandin HCO3 Water Water Hard faeces phase Hard faeces pellets Soft faeces phase CaecotrophsFigure 1.2. separating large quantities of food. Large particles of indigestible fibre are separated from small fermentable particles and fluid. The large particles are sent distally along the colon while the small particles and fluid are sent proximally into the caecum where bacte- rial fermentation takes place (Figure 1.2). The thin walled caecum ends in a narrow blind appendix that is heavily endowed with lymphoid tissue. The appendix is often described as ‘vermiform’ due to its worm- shaped appearance. The gut-associated lymphoid tissue (GALT) of the rabbit is predominantly in the hindgut and represents over 50% of the total lymphoid tissue, which may account for the relatively small spleen of rabbits (Percy and Barthold, 1993). The ascending colon of the rabbit is divided into four sections. At the proximal end, the ampulla caecalis coli opens into the first section that is approximately 10 cm long and has three longitudinal flat bands of muscular tissue or taeniae separating rows of haustra or sacculations. Small protrusions, approxi- mately 0.5 mm in diameter, can be seen on the mucosa in this section of colon. These cauli- flower-like protrusions have been termed ‘warzen’ (warts) and are believed to be unique 9Biological characteristics Figure 1.2. The activity of the digestive system during excretion of hard and soft faeces. The motility and function of the hindgut gut can change depending on the type of faeces that are formed within the colon. The formation of hard faeces is known as the hard faeces phase and the expulsion of caecotrophs is known as the soft faeces phase. The phases of excretion follow a marked circadian rhythm. The hard faeces phase is shown in black. The soft faeces phase is shown in green. Exchange of water, electrolytes and nutrients across the intestinal epithelium alter with the phase of faeces excretion. The direction of water and electrolyte exchange is indicated by arrows. The proximal part of the ascending colon is able to separate digesta into two fractions that are simultaneously sent in opposite directions. During the hard faeces phase, water is secreted into the proximal colon and the intestinal contents are thoroughly mixed by contractions of the caecum and colon. Large indigestible particles (> 0.5 mm) tend to accumulate in the lumen of the proximal part of the ascending colon and are moved distally, whereas smaller particles accumulate at the circumference in the sac-like haustra. Haustrum is the latin term for a pump. Haustral activity sends the small particles and fluid proximally into the caecum where bacterial fermentation takes place. The indigestible fraction, composed of large particles, is moved rapidly through the proximal colon to the fusus coli and distal colon where it is formed into hard, round, dry pellets that are excreted from the anus. Rhythmic caecal contractility is greatest during the hard faeces phase. Periodically, the motility of the caecum and proximal colon alters completely. Haustral activity ceases, the caecum contracts sending caecal material swiftly along the large intestine. In the fusus coli the material is formed into soft pellets that become encapsulated in mucus (see Plate 22). This is the soft faeces phase of excretion when caecotrophs pass through the colon to be expelled from the anus. Expulsion of caecotrophs coincides with a decrease in rhythmic motility of the caecum and proximal colon, and increase in motility of the distal colon. Soft faeces or caecotrophs are expelled one or twice daily, at least four hours after feeding, usually during periods of rest. The transit time for soft faeces through the colon is 1.5–2.5 times faster than for hard faeces. Motility in the upper gastrointestinal tract remains the same during the hard and soft faeces phases. The differences in colonic motility during the hard and soft faeces phase of excretion are most pronounced in the second section of proximal colon that has a single row of haustra. The fusus coli is a specially adapted area of the colon that acts as a differential pacemaker for the initiation of peristaltic waves in the proximal and distal colon that alter with the phase of faeces excretion. The fusus coli is highly innervated and is influenced by hormones such as aldosterone and prostaglandins. During the hard faeces phase, the intestinal contents lose considerable quantities of water, potassium and sodium during their passage through the fusus coli. Water is mechanically squeezed out of the fibrous material before it passes to the distal colon where absorption of water, volatile fatty acids and electrolytes continues leaving the residue of dry, indigestible matter that is expelled as hard faecal pellets. to lagomorphs. They represent an increase in the surface area of the colon that would favour increased absorption. The protrusions may also assist mechanical separation of intestinal contents. Histologically, the muscu- lar layers of the taenia contain many autonomic fibres that are part of the myenteric plexus (Snipes et al., 1982). The second section of ascending colon is approximately 20 cm in length and has a single taenia and fewer, smaller haustra. There is an abundance of myenteric plexus in this region. The third portion of the ascending colon is termed the fusus coli and is a muscular area about 4 cm long (see Plate 22). This area is highly inner- vated and vascular. The mucosal surface of the fusus coli is distinguished by prominent longitudinal folds and contains numerous goblet cells. The fusus coli opens into the fourth section of ascending colon that is histo- logically indistinguishable from the transverse and descending colon. Because the fusus coli forms such a natural division between two morphologically and functionally distinct sections of the rabbit colon, many physiologi- cal texts have abandoned the traditional description of ascending, transverse and descending colon and use the terms ‘proxi- mal’ and ‘distal’ colon instead (Snipes et al., 1982). The proximal colon includes the three taeniae section, the single taenia section and the fusus coli. The distal colon is 80–100 cm long and runs from the fusus coli to the rectum. The mucosa of the distal colon is smooth with no surface specialization. The tunica mucosa possesses short crypts with numerous goblet cells reaching into the base. This section of the colon is thin walled and usually contains hard faecal pellets. 1.5.3.1 Motility of the hindgut The motility and function of the hindgut gut can change depending on the type of faeces that are formed within the colon. The forma- tion of hard faeces is known as the hard faeces phase and coincides with feeding activity. The expulsion of caecotrophs is known as the soft faeces phase. The phases of excretion follow a marked circadian rhythm. In caged rabbits with ad lib access to food, feed intake increases from 15.00 to 18.00 h and remains high until midnight. Intake then reduces until 02.00 when a new phase starts with a maximum at 06.00 ending at 08.00 when the soft faeces phase begins. This natural pattern of feeding behaviour and faecal excretion can be seen in pet rabbits, although it may be altered by type and availability of food, age, pregnancy and lactation (Carabaõ and Piquer, 1998). During the hard faeces phase, water is secreted into the proximal colon, which aids the process of mixture and separation. Intestinal contents are thoroughly mixed by contractions of the caecum and colon that separate the digesta into large indigestible particles, and small particles including bacte- ria and water-soluble components. The indigestible fraction is moved rapidly through the proximal colon to the fusus coli and distal colon before being excreted from the anus. The fermentable fraction is moved in a retrograde direction back into the caecum. The large indigestible particles (> 0.5 mm) tend to accumulate in the lumen of the proximal part of the ascending colon and are moved distally, whereas smaller fermentable particles accumulate at the circumference in the sac-like haustra. Haustral activity sends the small particles proximally into the caecum. Caecal contrac- tility is greatest during the hard faeces phase when the liquid intestinal contents are mixed and separated in the proximal colon. Period- ically, the motility of the caecum and proxi- mal colon alters completely. Haustral activity ceases and caecal material is moved swiftly along the large colon. In the fusus coli the material is then separated into pellets that become encapsulated in mucus. This is the soft faeces phase of excretion. Soft faeces or caecotrophs are expelled at least 4 h after feeding, usually during periods of rest. The fusus coli is a specially adapted area of the colon that acts as a differential pacemaker for the initiation of peristaltic waves in the proximal and distal colon (Ruckesbusch and Fioramonti, 1976). The nature and direction of the peristaltic waves alter with the phase of faeces excretion. The fusus coli is highly inner- vated and is influenced by hormones such as aldosterone and prostaglandins. During hard faeces production aldosterone levels are high, but they fall during the soft faeces phase of excretion. Prostaglandins inhibit motility of the proximal colon and stimulate the distal colon aiding the elimination of soft faeces or caecotrophs (Pairet et al., 1986). 10 Textbook of Rabbit Medicine 1.6 Metabolism 1.6.1 Energy metabolism Volatile fatty acids provide an energy source for herbivorous species, such as rabbits, that utilize bacterial fermentation as part of the digestive process. The proportion and type of volatile fatty acids that are produced depend on the substrate that is metabolized and the species of bacteria that are present. In ruminants, the predominant volatile fatty acid is proprionate, which is produced by Lactobacillus species that are present in the rumen but are absent from the rabbit caecal microflora (Cheeke, 1987). In rabbits, acetates predominate followed by butyrate and proprionate with small quantities of isobu- tyrate, isovalerate and valerate. Increased amounts of fibre in the diet increase the proportion of acetate that is produced. Lactate is produced by bacterial fermentation within the caecotroph in the stomach and is subsequently absorbed during digestion of the caecotroph in the small intestine. Considerable energy is required by the hindgut for the metabolism and absorption of volatile fatty acids, electrolytes and other nutrients. This energy is mainly supplied by butyrate produced by Bacteroides spp. that predominate in the caecal microflora. Rabbit caecal-colonic epithelial tissue metabolizes butyrate without the production of ketone bodies. Volatile fatty acids absorbed from intestinal tract provide a regular energy source for the rabbit. Lactate enters the portal circulation from the stomach and small intes- tine while volatile fatty acids originate from the hindgut. Net absorption from the diges- tive tract is greatest during the hard faeces phase, which is matched by increased hepatic metabolism and the removal of propionate and butyrate from the circulation, leaving acetate and lactate available for extra-hepatic tissue metabolism (Carabaõ and Piquer, 1998). Due to alterations in hepatic metabo- lism, arterial concentrations of volatile fatty acids remain constant during both hard and soft phases of excretion, although their absorption and metabolism follow a circadian rhythm parallel to the activity of the adrenal gland (Vernay, 1987). 1.6.2 Water metabolism Rabbits normally drink 50–100 ml/kg/24 h (Brewer and Cruise, 1994) although this quantity is affected by the water content and composition of the diet. The complex diges- 13Biological characteristics • Digestion in the stomach and small intestine is similar to other monogastric animals • The colon of the rabbit is adapted to mix and separate large indigestible fibre particles from small digestible fragments and fluid • The indigestible and digestible fibre components of the diet are simultane- ously propelled in opposite directions in the proximal colon • Periodically, the pattern of motility in the large intestine and caecum changes completely to expel caecal contents as caecotrophs • A specially adapted area of the colon, the fusus coli, acts as a pacemaker to control colonic motility. The fusus coli is highly innervated and vascular and is influenced by blood metabolites and hormones such as prostaglandins and aldosterone • Small particles and fluid are directed in a retrograde direction from the proxi- mal colon to the large caecum where bacterial fermentation takes place. Volatile fatty acids are the products of bacterial fermentation • The substrate for caecal fermentation is composed of undigested food that reaches the colon plus excretion products, and substances such as mucopolysaccharides and desqua- mated cells from the digestive tract • Urea can diffuse into the caecum from the bloodstream to act as a nitrogen source for the caecal bacteria • The population of microorganisms within the caecum is finely balanced and changes with the time of day, caecal pH, and dietary substrate • Long particles of undigested fibre are propelled through the distal colon and expelled as hard faeces. Absorption and secretion of water, electrolytes and volatile fatty acids in the large intestine alter according to the type of faeces that is passing through • Indigestible fibre stimulates intestinal motility. tive processes of the rabbit require water to be continually absorbed and secreted along the gastrointestinal tract. Saliva is continu- ously secreted into the mouth and water is secreted into the stomach. In the caecum, water is absorbed from the contents, which contain 20–25% dry matter (Fekete, 1989). In the colon, absorption or secretion of water varies in each section of the colon and depends on whether hard or soft faeces are being formed. During the soft faeces phase, caecal contents pass through the colon with relatively little change in composition. During the hard faeces phase water is secreted into the proximal colon and mixed with intestinal contents. The water content of the digesta is highest immediately before the fusus coli and decreases sharply during the passage through the fusus and along the distal colon (Snipes et al., 1982). The complex exchange of water across the intestinal wall permits changes in hydration status without obvious fluid loss. The rabbit kidney differs from other mammalian species. In common with neonates and amphibians, there is a wide variation in the number of glomeruli that are active at any one time. Hydration, uncompli- cated by vasoconstriction, leads to a marked increase in glomerular activity. As much as a 16-fold increase in water diuresis is possible without significant change in glomerular filtration rate. When blood pressure is increased, there is little or no change in renal plasma flow (Brewer and Cruise, 1994). 1.6.3 Electrolyte exchange The absorption and secretion of electrolytes along the intestinal tract of the rabbit is complex. Saliva is continually formed by a two-stage process in which an isotonic fluid with a constant, plasma-like electrolyte composition is modified in the salivary glands (Fekete, 1989). Sodium and chloride are resorbed and potassium and bicarbonate are secreted. Bicarbonate is secreted into the duodenum and absorbed from the jejunum in which there is an inter-relationship between bicar- bonate secretion and sodium and chloride absorption. The caecal appendix secretes an alkaline fluid rich in bicarbonate that is also secreted in the proximal colon to moderate the rising pH due to volatile fatty acid production (Fekete, 1989). The transport of electrolytes across the colonic wall is regulated by aldosterone and is related to the type of faeces that is being produced. During the soft faeces phase, aldosterone concentrations are at their lowest and water, sodium and chloride are secreted while potassium is conserved. During the hard faeces phase, water and bicarbonate are secreted into the proximal colon and water, volatile fatty acids, sodium, potassium and chloride are absorbed from the distal colon thereby conserving water and electrolytes (Cheeke, 1987). 1.6.4 Acid–base balance The renal regulation of acid–base balance is different in rabbits in comparison with other domestic species. Rabbits have a limited ability to transfer hydrogen or bicarbonate ions between blood and urine because some metabolic pathways that are present in other species are absent or restricted. The enzyme carbonic anhydrase is absent from the thick ascending limb of the renal tubule of rabbits (Dobyan et al., 1982; Brewer and Cruise, 1994). In other species such as humans, monkeys and rats, carbonic anhydrase is present in the ascending tubule epithelial cells in large amounts. The enzyme is required for the rapid formation of carbonic acid that is an important step in the excretion of hydrogen ions and conservation of bicar- bonate. In other mammals, ammonia is produced in the kidney by glutamine deamination in response to a fall in plasma pH or a decreased concentration of bicarbonate. Ammonia acts as part of the buffering system in the renal tubule by combining with hydrogen ions before being excreted in the urine as ammonium ions. In rabbits, glutamine deami- nation only takes place in response to reduced serum bicarbonate concentrations but not a drop in plasma pH, which compro- mises the rabbit’s response to metabolic acidosis. In other species there are alternative biochemical pathways that result in ammonia synthesis but these pathways appear to be absent in the rabbit (Brewer and Cruise, 1994). 14 Textbook of Rabbit Medicine The rabbit also has problems correcting alkalosis. A large bicarbonate load can reach the kidney of rabbits as a result of bacterial fermentation in the gut and from tissue metabolism of acetate. In other species, bicar- bonate is neutralized by the products of ureagenesis and alkalosis is avoided. In rabbits, insufficient ammonium may be avail- able from tissue metabolism to neutralize bicarbonate, especially during periods of protein deficit (Brewer and Cruise, 1994). Alkaline secretion into the gut increases in response to metabolic alkalosis (Vattay et al., 1989). 1.6.5 Calcium metabolism Rabbits have an unusual calcium metabolism. It is characterized by total serum calcium concentrations that vary over a wide range and are 30–50% higher than other mammalian species (Buss and Bourdeau, 1984). Total serum calcium concentrations can reflect dietary calcium intake (Chapin and Smith, 1967a, b). Hypocalcaemia is rare, although lactation tetany can occur in nursing does (Barlet, 1980). Experimentally, hypocal- caemic tetany can be induced by parathy- roidectomy (Tan et al., 1987) or by feeding diets deficient in calcium or vitamin D (Chapin and Smith, 1967a; Bourdeau et al., 1986). It is not clear why rabbits have higher blood calcium levels than other species. Their calcium metabolism has been studied exten- sively. Experimentally, hypocalcaemia or hypercalcaemia can be brought about by the infusion of EDTA or calcium gluconate. Reciprocal elevations in PTH or calcitonin in response to EDTA or calcium gluconate infusion indicates that these hormones regulate serum calcium concentrations in rabbits as in other species (Warren et al., 1989; Bourdeau et al., 1986). However, rabbits appear to differ from humans in the level at which serum ionized calcium is set to initiate a parathyroid hormone (PTH) response (Warren et al., 1989). An analogy has been made with the syndrome of benign familial hypercalcaemia in humans that is a genetic condition characterized by hypercalcaemia without changes in renal function, blood pressure or any other potential sequels to chronic hypercalcaemia such as soft tissue mineralization. Not only do rabbits have higher total serum calcium concentrations than other species but they are also different in the way calcium is absorbed from the gut and excreted by the kidney. Calcium can be absorbed from the intestinal tract either by passive diffusion or by active transport across the mucosa. Active transportation involves a carrier protein that is synthesized in the intestinal mucosa in response to 1,25- dihydroxyvitamin D3, the active metabolite of vitamin D. A drop in serum calcium concen- tration stimulates PTH release which, in turn, stimulates the conversion of biologically inert 25-dihydroxyvitamin D3 to 1,25-dihydroxyvi- tamin D3 in the kidney, thereby indirectly increasing the absorption of calcium from the intestine. Calcium is not only absorbed from the gastrointestinal tract, it is also secreted into the gut across the intestinal mucosa. This process is independent of serum calcium concentrations and can take place in a hypocalcaemic animal. It has been demon- strated that secretion of calcium into the gut continues during periods of calcium depriva- tion in rabbits (Barr et al., 1991). In rabbits, passive intestinal absorption of calcium is efficient. If dietary calcium concen- trations are adequate, it appears that vitamin D is not required for calcium absorption (Bourdeau et al., 1986; Kamphues, 1991). However, vitamin D increases intestinal absorption of calcium and is required if dietary calcium levels are low (Brommage et al., 1988). Because it is absorbed passively, there is no feedback mechanism and calcium is absorbed in proportion to the dietary calcium concentration (Cheeke and Amberg, 1973). Blood calcium concentrations increase if dietary calcium levels are elevated. The rabbit kidney is capable of excreting or conserving calcium according to metabolic need. Responses are mediated by PTH and 1,25-dihydroxyvitamin D3 (Bourdeau et al., 1988). Tubular reabsorption of calcium by the kidney increases during periods of calcium deprivation (Bourdeau and Lau, 1992). During periods of high calcium intake the rabbit kidney is capable of increasing the fractional excretion of calcium into the urine considerably (Whiting and Quamme, 1984). 15Biological characteristics (1991). Effect of dietary calcium on bone density in growing rabbits. Am J Physiol., 260, E471–E476. Harkness, J.E. (1987). Rabbit husbandry and medicine. Vet Clin N Am: Small Anim Pract., 17, 1019–1044. Hirschfield, Z., Weinrab, M.M., Michaeli, Y. (1973). Incisors of the rabbit: morphology, histology and development. J. Dent. Res., 52, 377–384. Hörnicke, H., Ruoff, G., Vogt, B. et al. (1984). Phase relationship of the circadian rhythms of feed intake, caecal motility and production of soft and hard faeces in domestic rabbits. Lab Anim., 18, 169–172. Kamphues, J. (1991). Calcium metabolism of rabbits as an etiological factor for urolithiasis. J Nutr., 121, S95–S96. Kamphues, V.J., Carstensen, P. Schroeder, D. et al. (1986). Effect of increasing calcium and Vitamin D supply on calcium metabolism in rabbits (Article in German. English summary) J Anim Physiol Nutr., 50, 191–208. Kennedy, A. (1965). The urinary excretion of calcium by normal rabbits. J Comp Path., 75, 69–74. Lang, J. (1981). The nutrition of the commercial rabbit. Part 1. Physiology, digestibility and nutrient require- ments. Nutr abstr rev, Series B, 51, 197–217. Lazarus-Balow, P. (1928) The temperature of normal rabbits. J Pathol Bacteriol., 31, 517–524. Lelkes, L., Chang, C.L. (1987). Microbial dysbiosis in rabbit mucoid enteropathy. Lab Anim Sci., 36, 757–764. Lockley, R.M. (1978). The Private Life of the Rabbit. Andre Deutsch Ltd. McBride, A. (1988) Rabbits and Hares. Whittet Books Ltd. Nowak, R.M. (1999). Order Lagomorpha. In Walker’s Mammals of the World. Volume II,. 6th edn. pp 1715–1738. The Johns Hopkins University Press. Owen, D.G. (1992). Parasites of Laboratory Animals. Labora- tory Animal Handbooks No 12. Royal Society of Medicine Services Ltd. Pairet, M., Bouyssou, T., Ruckesbusch, Y. (1986). Colonic formation of soft feces in rabbits: a role for endogenous prostaglandins. (Abstract). Am J Physiol., 250, G302–G308. Patton, N.M. (1994). Colony husbandry. In The Biology of the Laboratory Rabbit. 2nd edn. (P.J. Manning, D.H. Ringler, C.E. Newcomer, eds). pp 28–44. Academic Press. Percy, D.H. and Barthold, S.W. (1993). Rabbit. In Pathol- ogy of Laboratory Rodents and Rabbits. pp 179–223. Iowa State University Press. Ruckesbusch, Y., Fioramonti, J. (1976). The fusus coli of the rabbit as a pacemaker area. Experientia, 32, 1023–1024. Ruckesbusch, Y., Pairet, M., Becht, J.L. (1985). Origin and characterization of migrating myoelectric complex in rabbits (Abstract). Dig Dis Sci., 30, 742–748. Sandford, J.C. (1996). The Domestic Rabbit, 5th edn. Black- well Science. Shadle, A.R. (1936). The attrition and extrusive growth of the four major incisor teeth of domestic rabbits. J Mammol., 17, 15–21. Snipes, R.L., Clauss, W., Weber, A., Hörnicke, H. (1982). Structural and functional differences in various divisions of the rabbit colon. Cell Tissue Res., 225, 331–346. Straw, T.E. (1988). Bacteria of the rabbit gut and their role in the health of the rabbit. J Appl Rabbit Res., 11, 142–146. Tan, S.Q, Thomas, D, Wellington, J.A.O. et al. (1987). Surgical thyroparathyroidectomy of the rabbit. Am J Physiol., 252, F761–E767. Vattay, P., Wenzl, E., Feil, W. et al. (1989). Role of acid base balance and mucosal blood flow in alkaline secre- tion of rabbit duodenum (Abstract). Acta Physiol Hung., 73, 81–87. Vernay, M. (1987). Origin and utilisation of volatile fatty acids and lactate in the rabbit: influence of the faecal excretion pattern. Br J Nutr., 57, 371–381. Warren, H.B., Lausen, N.C., Segre, G.V. et al. (1989). Regulation of calciotropic hormones in vivo in the New Zealand White rabbit. Endocrinology, 125, 2683–2689. Whiting, S.J., Quamme, G.A. (1984). Effects of dietary calcium on renal calcium, magnesium and phosphate excretion by the rabbit. Mine. Electrolyte Metab., 10, 217–221. 18 Textbook of Rabbit Medicine 2.1 Housing The quiet docile nature of the rabbit combined with its fertility and rapid growth rate has led to its intensive production for commercial and laboratory purposes. Units housing several thousand does are found in countries such as China, Hungary or the USA. At the other end of the scale, in the developing world, a few rabbits are often kept as ‘biological refrigerators’, i.e. a source of small quantities of meat that is fresh and readily available (Cheeke et al., 1982). The social and behavioural needs of such animals are ignored when they are housed individu- ally in small, wire mesh cages or confined to tiny hutches. There are many welfare impli- cations associated with keeping rabbits in cages, as they are not able to follow their natural instincts. Abnormal behaviour patterns such as stereotypies and restlessness have been recorded. Perpetual wire biting and pawing behaviour has been described in rabbits confined to small cages and does provided with an open nesting box and no bedding material to cover the young (Stauf- facher, 1992). A proven link has been estab- lished between small cage size and painful conditions such as skeletal disorders or ulcer- ative pododermatitis in intensively reared rabbits (Drescher, 1993; Drescher and Loeffler, 1996). Morphological differences have been observed in the adrenal glands of rabbits kept in wire cages and those kept in group housing conditions on solid floors (Drescher and Breig, 1993). In recent years, conditions have improved for many laboratory rabbits. They can be kept in social groups of four to eight animals with no detriment to their health (Turner et al., 1997). It has been proven that rabbits prefer to be in proximity with each other and ‘inter- act with enrichment objects’ such as wooden sticks, parrot toys or balls designed for cats (Huls et al., 1991). Keeping rabbits in this way not only benefits the rabbits but also the people looking after them. Love (1994) described the response of animal technicians to group housing by saying they ‘found it more agreeable to work with rabbits that came to the front of the cage when they heard the sounds of people, rather than cowering away’ and ‘it was a pleasure to see the rabbits interact with each other’. Stauffacher (1992) describes in detail many ways in which housing for rabbits can be constructed to permit natural behaviour patterns. Despite these advances, most breeding and exhibition rabbits still live their entire life confined to small cages. Some breeders still insist that rabbits should be kept singly in small cages and that large hutches and runs lead to aggression and behaviour problems (Sandford, 1996). At last, the pet owning fraternity is becoming aware of the rabbit’s social nature and need for exercise. There has been a steady increase in the number of house rabbits and the status of the rabbit has shifted from the child’s pet to a member of the family. A rabbit can be a satisfactory compan- ion for adults that are out at work all day and find the needs of a dog or cat too demanding. Hopefully the days of keeping pet rabbits in solitary confinement in a barren hutch at the bottom of the garden are now coming to an end. There is legislation governing the welfare of rabbits that is summarized in Box 2.1. Diet and husbandry 2 Rabbits have been used as foster mothers for ostrich chicks with benefits for both ostriches and rabbits (Madeiros, 1997). The ostrich chicks and rabbits have a strong affin- ity for each other. The rabbit provides a mother figure for the ostrich that is intro- duced as a day old hatchling. By 6–8 weeks the ostrich chick becomes independent. 2.2 Hutches for pet rabbits Traditionally, pet rabbits are kept in hutches in the garden, shed or garage. Hutches are a convenient method of housing rabbits, but it is important to provide time for exercise each day. At least 4 h daily exercise is required (Richardson, 2000). Longer periods or unrestricted exercise are preferable. The hutch should be as big as possible, especially if two rabbits are housed together. It needs to be situated in a dry, cool, well- ventilated site protected from wind and rain. Poor ventilation and ammonia build-up predispose to conjunctivitis and respiratory tract infections. It is preferable to situate the hutch against a sheltered wall outside, rather than in an enclosed, stuffy shed or garage. Rabbits are tolerant of cold conditions and can withstand winter weather provided they have shelter and plenty of bedding material. Thin rabbits with no body fat are more susceptible to the effects of cold and need extra protection on cold nights. Hot condi- tions and direct sunlight with no shade are distressing for rabbits as they cannot sweat or pant effectively. The optimum temperature range for rabbits is 15–20°C, which can be checked with a maximum and minimum thermometer. Rabbits produce copious quantities of urine and faeces, which are usually deposited in one part of the hutch that should be cleaned once or twice daily. A litter tray, which can be washed and cleaned easily, can be placed in that area of the hutch. Most rabbits will use a litter tray. Many free- range rabbits will return to an open hutch or covered area especially to use their tray. Bedding that is not fouled and remains clean and dry can be left in the hutch. Many types of material can be used as bedding. Garden peat has been recommended to neutralize ammonia and reduce irritation to the eyes and respiratory tract (Malley, 1995). An economical bedding material is a layer of 20 Textbook of Rabbit Medicine Box 2.1 Legislation governing the welfare of rabbits There is legislation governing the welfare of farmed rabbits in the UK. The advice also applies to pet rabbits kept in hutches although they are not technically covered by the legislation. Separate legislation governs the transport and slaughter of rabbits. A guide to the legal requirements for farmed rabbits has been produced by UFAW (Universities Federation for Animal Welfare) and can be summarized as follows: Rabbits must be provided with: • Adequate lighting to enable the inspection of the animals at any time. • Wholesome food that is appropriate and in sufficient quantity to maintain good health and satisfy nutritional needs. • A daily supply of fresh drinking water. • Suitable accommodation with a suitably bedded floor for the isolation of a sick or injured rabbit. • Cages of sufficient size to allow the rabbits to move around, feed and drink without difficulty, and allow all the rabbits kept in them to be able to lie on their sides at the same time. • Cages of sufficient height to allow rabbits to sit upright on all four feet without their ears touching the top of the cage. • Shelter from bad weather including direct sunlight. • Daily inspection of all automatic equip- ment, such as drinkers, by a competent person. • An alarm on automatic ventilation systems that is independent of the mains electric- ity and will give warning when the system fails to function properly. • Daily inspection of stock and the preven- tion of unnecessary suffering or distress. • Veterinary care. Prescription only medicines (POM) including antibiotics and vaccines can only be supplied by the veterinary surgeon that has the rabbits in his/her care. 2.7 Free-range rabbits Stauffacher (1992) described the behaviour of rabbits in ‘near-to-nature’ or free-range condi- tions. The rabbits were kept in an open-air turfed enclosure with several trees and bushes. They were kept in groups of up to 30 animals and their daily activities followed a double diurnal rhythm with periods of rest alternating with periods of activity around dusk and dawn. During periods of rest, the rabbits sought out places with a good overview of the enclosure under bushes or near trees where they would huddle together and engage in mutual grooming. This method of husbandry permits natural behaviour patterns, encourages grazing and normal caecotrophy and allows animals to groom themselves and each other thoroughly thereby removing skin debris, dead hair and parasites from the coat. In a study by Harcourt-Brown and Baker (2001) blood samples from rabbits kept under free-range conditions had higher red cell and lympho- cyte counts than rabbits kept in hutches, suggesting that they were healthier (see Figure 6.1). 2.8 House rabbits In recent years, there has been a trend to give pet rabbits the run of the house. House rabbits make good companions and can be trained to use a litter tray. They are usually provided with some sort of sleeping accom- modation to which they can retreat and can be confined while their owners are out at work. Most house rabbits are neutered, especially males, to reduce territory marking by spraying or defaecating outside the litter tray. Rabbits can bond closely with human owners and make entertaining responsive pets. They will play with toys, beg for treats and follow their human companion around the house. Dogs and cats can learn to tolerate rabbits as companions. 2.9 Litter trays Large cat litter trays or gravel trays from the garden centre can be used for rabbits to urinate and defaecate in. Hay, straw, cat litter, peat, soil or ‘natural’ litters made from hemp, corn cobs or reclaimed wood pulp are all used as litter materials for rabbits. Clay litters are not advisable as some rabbits will eat the litter which can impact the caecum (Brown, 1997). Organic solvents in litter materials derived from preserved pine wood shavings or cedar chips have been reported to cause hepatotoxicity and are therefore inadvisable (Rabbit Health News, 1991). Hay or clean, chopped straw can be used in rabbit litter trays. 2.10 Breeds of rabbits Domestication has resulted in a wide range of breeds with different attributes. They can be roughly divided into two groups; fancy breeds and fur breeds (Sandford, 1996). The fur breeds include Rex, Angoras and Satin rabbits with their beautiful coat textures. Fancy breeds include the Belgian Hare, Lop and Dwarf rabbits with their varying physi- cal characteristics. Most pet rabbits belong to the smaller breeds such as Dwarf lops, Dutch or English. Pedigree rabbit breeders often sell surplus stock to the pet trade and occasion- ally one of the more obscure breeds may turn up as a pet. Pedigree stock is identified by aluminium rings slipped over the hock when the rabbit is 8–10 weeks old. The rings are supplied by the British Rabbit Council in a range of sizes. Each ring has the year of birth and a unique number from which the rabbit can be identified. Many pet rabbits are the result of interbreeding between pets and are cross breeds. As with other domestic animals, there are breed predispositions to disease. For example, Dwarf rabbits are prone to congen- ital incisor malocclusion (Fox and Crary, 1971). Dutch, Havana and Tan rabbits have a high incidence of uterine neoplasia (Greene, 1941). 2.10.1 Angoras Angoras have been bred for wool production for hundreds of years. The wool is plucked or sheared and either spun on its own or mixed with sheep’s wool. Plucked wool is superior to shorn wool. Commercial Angoras are kept in a specialized manner to prevent staining 23Diet and husbandry and matting of the fur. After defleecing, woollen jackets can be worn for 2–3 weeks to reduce heat loss or a strip of fleece can be left along the back (Lebas et al., 1998). Commer- cial Angoras are not provided with bedding but are kept on wire mesh floors and hay is provided in a rack. The long fine coat is a definite disadvantage for the pet animal as it difficult to keep the rabbit free from knots and mats. It is not surprising that a high number of Angoras arrive at rescue shelters for rehoming. The breed is prone to intestinal obstruction by felts of ingested hair. 2.11 Nutrition Rabbits are strict herbivores with a digestive system that is adapted to the ingestion of a high fibre diet. Digestive physiology is described in Section 1.5. Briefly, indigestible fibre is separated from fermentable compo- nents in the proximal colon and is rapidly eliminated in hard faecal pellets. The fermentable components, which consist of small particles and fluid, are moved back into the caecum where bacterial fermentation takes place to release volatile fatty acids that are absorbed as an energy source. Caecal contents are expelled periodically as mucous encapsulated caecotrophs that are reingested and digested as a source of amino acids and vitamins. This strategy permits the digestion of large volumes of fibrous foods without storage in the gastrointestinal tract. Digestion can take place when the rabbit is below ground and not vulnerable to predation. Since their domestication, rabbits have been fed on a variety of diets. During the last war in the UK, when food was scarce, backyard rabbits were kept as a source of protein that could survive on weeds, household scraps and foods that the producer could grow himself. This still occurs in many developing countries where rabbits are fed on a range of forage materials. Large-scale rabbit produc- tion has led to the development of pelleted foods of known analysis suitable for commer- cial rabbits. The nutritional requirements for pregnancy, lactation, growth and fur produc- tion have been well researched but the requirements for long-term maintenance of unproductive rabbits has been overlooked. Nutritional disease is common in rabbits kept as pets. For owners, providing food that is eaten readily and enjoyed is one of the most rewarding aspects of keeping a rabbit. The visual appearance of food influences the owner when choosing a product, so pelleted diets have become unpopular and a wide range of visually attractive, highly coloured cereal mixes have evolved as ‘rabbit food’ in the UK. These diets are cheap to produce and many are put together by food compounders that normally make rations for farm animals. The choice of ingredients is based on general nutritional principles combined with cost and availability of ingredients. Scientific, long- term feeding trials are not carried out. The nutrient value, vitamin and mineral content of a diet is calculated by extrapolating figures taken from data tables of ingredients rather than analysing the food itself. The recent trend towards convenience foods for both humans and their pets has resulted in owners purchas- ing rabbit food from the local supermarket or pet shop rather than preparing their own. There are many myths and old wives’ tales about feeding rabbits that unnerve the owner and dissuade them from home-produced diets and drive them to the apparent safety of commercial rabbit foods. Unfortunately, most commercial foods do not provide the ideal diet for a pet rabbit. Dietary recommendations for pet rabbits are described in Box 2.7. 24 Textbook of Rabbit Medicine Key points 2.1 • Hutches are not suitable for rabbits to be kept in all the time • Daily exercise is vital for physical and mental health of rabbits. At least 4 h exercise daily is recommended, includ- ing during the winter months • Rabbits benefit from companionship and form close bonds. The ideal companion is another rabbit, preferably of the opposite sex. Neutering is required • Rabbits each have their own character. Some individuals are sociable, others are not • Laboratory rabbits are often group- housed. It is possible to keep social groups of up to eight animals • Most rabbits naturally use a litter tray • Angoras do not make easy pets due to the demands of grooming their long, fine coat. 2.12 Appetite Hunger is stimulated by a drop in blood glucose, lactic acid, amino acids and volatile fatty acids. Dryness of the mouth and contractions of the stomach stimulate eating (Fekete, 1989). The volume of food that is eaten is influenced by its composition and texture and by the individual likes and dislikes of the rabbit. Increasing the fibre content of the diet increases the total volume that is consumed (Bellier and Gidenne, 1996). Rabbits will eat a variety of foods but show a preference for fibre and may eat hay or straw in preference to their compound feed. It can be difficult to persuade rabbits to eat new foods once they have become accustomed to a particular diet. New batches of food may be refused despite it appearing to be exactly the same to the owner. Sweet foods are generally palatable. Molasses are used in many commercial rabbit foods to improve palata- bility (Cheeke, 1994). Bitter tastes such as the saponins in alfalfa are well tolerated (Cheeke, 1987). Most rabbits enjoy leafy plants. A whole variety of plants can be eaten including many garden weeds and ornamental plants (see Box 2.7). Sunflower leaves were found to be most palatable in a study by Harris et al. (1983). Rabbits appear to enjoy foods of different textures. Pellets are preferable to ground meal. Biscuits or hard pieces of breakfast cereal are accepted readily. Bark is stripped from young trees or shrubs. All parts of the plant may be eaten including the stem and roots, although the growing tips are usually nibbled off first. Tree leaves are eaten, especially in the autumn when the leaves fall. Like many activities in rabbits, appetite follows a diurnal pattern. Wild rabbits feed at dusk and dawn. Pet rabbits may not be hungry during the day and are most likely to eat in the early evening or overnight. 2.13 Dietary requirements of rabbits 2.13.1 Carbohydrate Carbohydrates are compounds of carbon, hydrogen and oxygen with the empirical formula of (CH2O)n where n is > 3. Some molecules contain phosphorus, nitrogen or sulphur and not all follow the (CH2O)n rule, e.g. deoxyribose C6H10O4. Carbohydrates can be classified according to the complexity of their structure, i.e. monosaccharides, oligo- saccharides, polysaccharides and complexed carbohydrates such as glycoproteins. Alterna- tively, they can be categorized into sugars, starches and fibre. Fibre is expelled undigested (indigestible fibre) or fermented in the caecum to produce volatile fatty acids (digestible or fermentable fibre). Carbohydrates are an important energy source. They can be digested and absorbed from the stomach and small intestine or degraded and fermented by the caecal microflora. Simple monosaccharide sugars such as glucose, fructose and galactose are absorbed from the small intestine in a similar manner to other species. Starches are polysac- charides that are abundant in seeds, fruits, tubers and roots and are broken down to simple sugars during digestion. The reaction is catalysed by amylase that is secreted by the salivary glands and pancreas and is also present in caecotrophs as a result of bacterial synthesis. The age of the rabbit, dietary levels and the type of starch influence digestion and absorption in the small intestine. For example, cereal starches are more fermentable than those found in roots or tubers. Starch is found in plants as granules that are insoluble in cold water, but when a suspension of starch in water is heated, the granules swell and eventually gelatinize. Gelatinized starches can form complexes with proteins that reduce the digestibility of both starch and protein (Cheeke, 1987). Feed manufac- turing processes and exogenous enzymes supplements also affect starch digestibility (De Blas and Gidenne, 1998). Starch that is not digested and absorbed in the small intestine passes into the caecum as a substrate for bacterial fermentation. Residual starch that reaches the caecum or ‘carbohydrate overload’ is thought to be a predisposing factor in the development of enterotoxaemia in young rabbits. Clostridium spiroforme requires glucose as a substrate for iotatoxin production and glucose is yielded during bacterial fermentation of carbohydrate (Cheeke, 1987). In commercial units, entero- toxaemia is seen in young rabbits in associa- 25Diet and husbandry 2.13.2.2 Digestion of fermentable fibre within the caecum In rabbits, there is evidence that partial diges- tion of fibre can take place in the stomach and small intestine by the action of enzymes such as pectinases and xylanases (Gidenne et al., 1998). However, most digestion of fibre takes place by the microbial flora within the caecum. Digestibility within the caecum depends on the nature of the plant material and, to a lesser extent, processing procedures. Hemicelluloses and pectins are broken down more easily than cellulose, which requires degradation by cellulolytic bacteria and requires time for attachment of the bacteria to the cell wall before degradation starts. Degra- dation of cellulose takes longer than hemicel- lulose because of its linear polymer structure (Gidenne et al., 1998), so it is less fermentable than hemicellulose. Cellulose can be closely associated, both chemically and physically, with other compounds such as hemicellulose and pectin and affect their digestibility. It can also be combined with lignin that is almost completely indigestible. The digestibility of fibre within the caecum affects the rabbit’s appetite and growth rate. Grinding down lignin so that it passes into the caecum depresses voluntary food intake in compari- son with cellulose that is more fermentable (Chiou et al., 1998). The chemical structure of fibre molecules gives them a buffering capacity that is depen- dent on the concentration of carboxyl, amino and hydroxyl groups (Gidenne et al., 1998). The type of fibre has an effect on caecal pH which, in turn, can affect the balance of caecal microflora. For example, wheat straw tends to increase caecal pH, whereas beet pulp decreases it. Balanced sources of fibre such as alfalfa do not modify caecal pH (Gidenne et al., 1998). Particle size within the caecum affects retention time for microbial fermentation (Gidenne et al., 1998). Small particles have a larger surface area for bacteria to adhere to. The particle length of fibre depends on the plant source and processing procedures. Digestibility of lignified material can be increased by alkali treatment to dissolve lignin and release cellulose and other compounds for microbial degradation. Grind- ing down lignin to small particles allows it to be retained in the caecum where it cannot be digested. The degree of grinding is an impor- tant consideration as it alters the way in which fibre is separated in the proximal colon. Grinding fibre to particles small enough to be moved into the caecum rather than colon detracts from the beneficial effect of indigestible fibre on intestinal motility. There is general agreement that screen sizes for production of complete compound feeds should be 2 mm. Screen sizes of 1 mm induce digestive upsets (Lowe, 1998). Some cell wall constituents, such as pectins and gums, are hydrophilic and tend to form gels in solution. This property is used to produce bulk laxatives in humans because the compound takes up water in the digestive tract and increases the volume of faeces and promotes peristalsis. In rabbits, these compounds are moved into the caecum where they absorb water and increase retention time. Caecal impactions have been associated with the use of bulk laxatives in rabbits. 2.13.2.3 The importance of indigestible fibre Rabbits have a natural appetite for fibrous foods. They will strip and eat bark, chew roots and dried fibrous vegetation and may eat hay in preference to fresh green foods. Indigestible fibre plays an important role in maintaining good health in rabbits. Chewing and grinding food wears the teeth and helps to maintain normal dental occlusion. A diet deficient in fibrous material has been impli- cated in cheek tooth overgrowth (Crossley, 1995). Diets low in indigestible fibre predis- pose to gastrointestinal hypomotility and the retention of food and hair in the stomach, which forms trichobezoars (hairballs). Slow gut motility and increased food retention time in the hindgut can result in alterations in gut flora and the development of enterotox- aemia. The provision of a diet high in indigestible fibre to house rabbits reduces the ingestion of non-food items such as carpet fibres or plastic litter trays. Fur chewing and barbering is also linked to low fibre diets (Quesenberry, 1994). Diets containing low dietary fibre depress voluntary food intake (Bellier and Gidenne, 1996). Fibre has an effect on caecotrophy. The amount of fibre in the diet affects the time 28 Textbook of Rabbit Medicine that digesta is retained in the caecum for microbial fermentation. Carabaõ et al. (1988) measured the weight of soft faeces that were produced by rabbits fed varying levels of fibre. The weight of soft faeces was then compared to the weight of caecal contents. They found that a relatively small amount of the caecal contents were removed each day in rabbits fed diets containing less than 14% fibre. In rabbits consuming a diet of greater than 14% fibre, the caecal material was almost entirely removed each day. Diets high in indigestible fibre increase the rabbit’s appetite for caecotrophs (Fekete and Bokori, 1985). The fibre content of caecotrophs is propor- tional to the crude fibre level of the diet, although their dry matter content is unaffected by changes in dietary fibre content (Carabaõ et al., 1988). Indigestible fibre has no effect on the composition of caecotrophs because large fibre particles do not enter the caecum and are excreted in the hard faecal pellets. 2.13.2.4 Recommended dietary fibre for rabbits The fibre content of a diet is often expressed as ‘crude fibre’. This term refers to the percentage of the original food that remains after boiling in acid and alkali alternately. Crude fibre is mainly a measurement of the lignin and cellulose component of the diet and does not include other fermentable fibre components. Neither does crude fibre analy- sis give an indication of particle length or the effect on gut motility. An alternative measurement of fibre is ‘neutral detergent fibre’ (NDF) and ‘acid detergent fibre’ (ADF). The NDF is made up of cell wall constituents – pectins, cellulose, hemicellulose, lignin etc. ADF is the residue of NDF after acid extraction of the feed sample and is mainly indigestible lignocellu- lose complex. Digestible hemicellulose is the difference between NDF and ADF. ADF gives a better indication of indigestible fibre content than crude fibre. Recommended dietary fibre levels for rabbits vary between texts. In many cases, crude fibre figures are given that are not particularly helpful. Dietary fibre require- ments have been determined for commercial rabbits but not for pet ones. Rabbits that are used for meat production need to grow rapidly and convert food efficiently. The digestibility of the fibre content of the diet is an important consideration for peak perfor- mance. The importance of indigestible fibre is often overlooked. It is known that less than 10% crude fibre results in caecal acidosis and results in a high incidence of enteritis. Crude fibre levels of 10–15% are recommended for commercial rabbits for optimal growth rates (Cheeke, 1987). In contrast to commercial rabbits, pet rabbits are not growing and do not need to convert food efficiently. The indigestible fibre component of the diet is of greater impor- tance than fermentable fibre. In pet rabbits, it is important to promote intestinal motility and prevent obesity. Lowe (1998) recom- mends crude fibre levels of 13–20% for pet rabbits with a level of 12.5% indigestible fibre. Jenkins (1991) recommends a level of 18–24% fibre for pet rabbits, although the type of fibre is not specified. The fibre analysis of some ingredients of rabbit foods is summarized in Table 2.1. For pet rabbits, a permanent source of indigestible fibre such as ad lib grass or hay will ensure adequate fibre levels as long as the rabbit actually eats it. Soiled, unpalatable hay or underlying dental disease can substan- tially reduce indigestible fibre intake. 2.13.2.5 Sources of fibre for pet rabbits Concentrated foods usually include a fibre source, such as grass or alfalfa. The fibre has to be processed in some way to incorporate it into the food, which can affect its digestibil- ity and its effect on gut motility. Grass and hay are good sources of fermentable and indigestible fibre for rabbits. Hay can be provided in addition to, or instead of grass. It is not only a source of fibre but also enriches the environment and prevents abnormal behaviour (Berthelsen and Hansen, 1999). Alfalfa is a source of fibre that is used in commercial rabbit diets in many countries. Alfalfa hay not only provides fibre but has a high calcium content. Alfalfa hay is not generally available in the UK. Instead, meadow hay suitable for feeding to pet rabbits is available from most pet shops. Meadow hay is preferable to alfalfa for pet rabbits. Fresh grass is the ideal food and 29Diet and husbandry rabbits have evolved to live on it. Garden weeds are also a source of fibre and give variety to the diet. Pet rabbits that are allowed free access to a garden will browse on a selection of plants. They have their own individual likes and dislikes and will eat tough fibrous vegetation as well as soft new shoots. Tree leaves are eaten, especially in the autumn when the leaves have fallen and are within easy reach. Leaves from apple and hazel are especially enjoyed by rabbits (Richardson, 1999). Bark may be stripped from branches and from the base of trees. Exposed roots may be chewed through. Young docks, brambles, raspberry leaves, sow thistle, chickweed, groundsel, dande- lions, clover, plantain, goose grass, ground elder and vetches are among a host of plants that are enjoyed by pet rabbits. Unfortu- nately, annual bedding plants, herbs and other decorative garden shrubs will also be enjoyed and destroyed by a rabbit that is given the run of the garden. Fresh fruit and vegetables can be fed as an additional source of fibre, especially when natural vegetation is scarce. Broccoli, brussels 30 Textbook of Rabbit Medicine Table 2.1 Fibre analysis of some rabbit foods Analysis on dry matter basis Crude fibre: The crude fibre content is determined by boiling an ether extracted food sample in dilute acid and alkali alternately before burning in a furnace. The difference in weight before and after burning is the crude fibre fraction. This is not an accurate measurement as many cell wall components are destroyed during process. Historically, this is the measurement that is included in food analysis tables (Cheeke, 1987). Neutral detergent fibre (NDF) is the percentage of food remaining after boiling in neutral detergent that leaves most components of cell wall intact. Acid detergent fibre (ADF) is the percentage of neutral detergent fibre (NDF) that remains after boiling in acid which removes the hemicellose component. Indigestible fibre is represented by ADF. Hemicellulose is represented by difference between NDF and ADF. Hemicellulose is fermented in the caecum. Ingredient Crude fibre (%) NDF (%) ADF NDF-ADF Comments (indigestible (hemicellulose fibre guide) content) (%) (%) Alfalfa 30.2 49.3 37.5 11.8 Beet, sugar 20.3 32.1 17.9 14.2 High in starch and sugars Beans 8 16.8 12.3 4.5 Bran 11.4 47.5 13.7 33.8 Cabbage 17 24.4 13.6 10.8 Carrots 9.4 13.4 Grass, dried 21 54.1 28.2 25.9 Grass growing 13 57.7 29.6 28.1 Fibre content varies with stage of growth Hay (poor quality) 38 74.1 45.2 28.9 Hay (good quality) 29.8 65 36.4 28.6 Kale 17.9 24.3 19.7 4.6 Maize 2.4 11.7 2.8 8.9 High in starch Oats, rolled 10.5 31 14.9 16.1 High in starch Oats, naked 4.5 11.4 4.2 7.2 High in starch Peas 6.3 11.6 7.6 4 Straw (Wheat) 41.7 80.9 50.2 Swedes 10.0 14 12.5 1.5 High in starch Reference sources: Rabbit Feeding and Nutrition (1987) Cheeke, P. Academic Press. San Diego. Animal Nutrition 5th Edition (1995) McDonald, P. et al., Longman Ltd. 2.13.5 Fats The digestion and absorption of fats in rabbits is similar to monogastric animals. Fat globules are emulsified by the action of bile salts before being broken down by pancreatic lipase and absorbed from the small intestine. Fats and oils have been used in rabbit rations to provide an energy source that avoids carbohydrate overload of the hindgut. Dietary fat reduces intestinal absorption of calcium due to the formation of calcium soaps in the gut. Fat stimulates gastrointestinal motility and improves palatability of the diet. Vegetable oils are more digestible than animal fats (Cheeke, 1987). The fat content affects the keeping quality of pellets and the cost of production. For pet rabbits, high dietary levels of fats and oils are disadvantageous due to the propensity of rabbits to become obese. High fat diets increase the risk of hepatic lipidosis by altering lipid metabolism and promoting ketogenesis and hypoglycaemia during periods of starvation (Jean-Blain and Durix, 1985). Obese animals with a fatty liver are at great risk of developing fatal fatty degenera- tion of the liver and kidneys if they become anorexic. Most commercial diets contain 2.5–4.0% fat, but treat foods such as chocolate drops or sweet biscuits contain higher amounts. 2.13.6 Vitamins 2.13.6.1 Vitamin A Vitamin A, or retinol, is a fat-soluble, organic alcohol formed in animal tissues from caretenoid pigments in plants of which
- carotene is the most important.
-carotene is converted to vitamin A primarily in the intestinal mucosa and is stored in the liver, from which it is transported, protein bound, to cells according to metabolic need. Vitamin A is necessary for vision, bone development, maintenance of epithelial integrity, reproduction and immunological response. Retinol makes up part of a retinal pigment, rhodopsin, which is necessary for vision, especially in dim light. Vitamin A is required by epithelial tissue and deficiency results in squamous metaplasia and keratinization. Vitamin A also plays an important role in combating infection and has been termed the ‘anti-infective vitamin’. In several species, vitamin A deficiency is accompanied by low levels of immunoglobu- lins, although the exact function of the vitamin in the formation of these proteins is unknown (MacDonald et al., 1996). Growth and reproduction are affected by vitamin A deficiency. Excessive quantities of vitamin A lead to toxicity with symptoms similar to those of deficiency. The vitamin A content of plants varies considerably. The long hydrocarbon chain is easily oxidized especially when exposed to heat, light, moisture and heavy metals (McDonald et al., 1996). Exposure to sunlight during the curing process destroys much of the vitamin A in hay or alfalfa. Storage and rancidity of feeds also reduces vitamin A content, although the addition of antioxidants can reduce the loss. Cereals, with the excep- tion of yellow maize, are poor sources of vitamin A. Grazing animals generally obtain more than adequate amounts of vitamin A from pasture and build up liver reserves. Deficiency is rare in farm animals that are fed on silage and well preserved hay over the winter months, although vitamin A deficiency has been reported in cattle housed indoors on high cereal rations (McDonald et al., 1996). Rabbits housed indoors or in hutches and fed on cereal mixtures and poor quality hay are candidates for vitamin A deficiency if they do not eat the parts of the diet that contain the vitamin and mineral supplement. Because of the role of vitamin A in the maintenance of epithelial tissues and mucous membranes, deficient animals are susceptible to disease and infection. A high incidence of enteritis occurs in vitamin A deficient rabbits (Cheeke, 1994). Experimental vitamin A deficiency has been studied in rabbits. Retarded growth and weight loss occur in growing animals with the development of neurological symptoms in severe cases. Hydrocephalus and cerebellar herniation can occur in immature rabbits (Phillips and Bohstedt, 1937). In the adult, eye lesions can be the first sign of deficiency with the development of keratitis that progresses to iridocyclitis, hypopyon and permanent blind- 33Diet and husbandry ness (Hunt and Harrington, 1974). Lacrimal gland tissue and the bone surrounding the optical foramen has found to be unaffected by vitamin A deficiency, although these tissues are affected in other species (Fox et al., 1982; Ubels and Harkema, 1994). Reproductive problems such as fetal malformations, low fertility and abortions have been associated with both vitamin A deficiency and excess (Cheeke, 1987). Intercurrent disease such as hepatic coccidiosis due to Eimeria steidae infec- tion can interfere with vitamin A metabolism and therefore increase dietary requirement. Vitamin A activity is expressed in interna- tional units (IU) and the dietary requirement for rabbits appears to be 10 000–18 000 IU/kg (Lowe, 1998). Fresh green foods and grass are good sources of vitamin A. 2.13.6.2 Vitamin D Vitamin D is a fat-soluble vitamin that is also a hormone, which plays an important role in calcium and phosphorus metabolism. A vitamin is defined as ‘an organic substance found in foods that is essential in small quantities for growth, health and survival’ (Blood and Studdert, 1999). A hormone is defined as ’a chemical transmitter substance produced by cells of the body and trans- ported by the bloodstream and other means to the cells and organs which carry receptors for the hormone and on which it has a specific regulatory effect’ (Blood and Studdert, 1999). Therefore vitamin D is both vitamin and hormone and has a range of physiological effects in addition to its role in calcium metabolism. Vitamin D receptors are found in many tissues including the stomach, brain, pituitary gland, gonads, parathyroid glands, epidermis, dermis, monocytes and activated T and B lymphocytes, although the exact physiological action in these tissues is unclear (Holick, 1990). There are several metabolites of vitamin D that are either ingested in the diet or synthe- sized in the body. The number of terms and abbreviations that refer to vitamin D and its metabolites can be confusing. These terms are defined in Box 2.4. Ultraviolet light is required to convert an endogenous vitamin D precursor, 7-dehydro- cholesterol, to pre-vitamin D3 in the skin. Further conversion to vitamin D3 (cholecalcif- erol) takes place before it is transported to the liver, bound to plasma protein. Plants contain a different vitamin D precursor, ergosterol, which is also converted by ultraviolet light to produce ergocalciferol or vitamin D2. This process takes place in the plant when vegeta- tion, such as hay, dries in the sunshine. Ergocalciferol is transported, protein bound, from the gut to the liver where, like vitamin D3 (cholecalciferol), it is hydroxylated to form 25-hydroxycholecalciferol (25-OH-D) which is, in turn, converted to the active vitamin D metabolite 1,25-dihydroxycholecalciferol (1,25(OH)2D) in the kidney. Conversion of 25- OH-D to 1,25(OH)2D is stimulated by parathyroid hormone (PTH) released from the parathyroid gland in response to low serum calcium concentrations. 34 Textbook of Rabbit Medicine Box 2.4 Definition of terms relating to vitamin D Vitamin D: A group of closely related steroids with anti-rachitic properties Vitamin D2 (Ergocalciferol, calciferol): An exogenous provitamin formed from ergosterol in plants when they are exposed to ultraviolet light. Vitamin D2 is converted to 25-OH-D in the liver Vitamin D3 (Cholecalciferol): An endogenous provitamin that is converted to 25-OH-D in the liver Vitamin D4 and D5: occur naturally in the oils of some fish* Ergosterol: A sterol that occurs in plants. It is converted to vitamin D2 under exposure to ultraviolet light 7-dehydrocholesterol: A derivative of chlolesterol that is metabolized to vitamin D3 in skin exposed to ultraviolet light 25-OH-D (25-hydroxycholecalciferol, calcifediol, 25-dihydroxyvitamin D): a metabolite of vitamin D that is formed and stored in the liver. There is a negative feedback controlling the conversion of provitamins (vitamin D2 and D3) to 25-OH- D 1,25(OH2)D (1,25-dihydroxycholecalcif- erol, calcitriol, 1,25-dihydroxyvitamin D): The active metabolite of vitamin D that is formed in the kidney from 25-OH-D under the influence of parathyroid hormone (PTH) that is released in response to low serum calcium concentrations. *From Blood, Henderson and Radostits (1979). The main function of vitamin D is to maintain serum calcium levels within the normal range. This is achieved by its effects on the intestinal absorption of calcium, mobilization of calcium to and from bone and renal regulation of calcium excretion. 1,25(OH)2D stimulates intestinal absorption of calcium and osteoclastic activity in bone. High quantities of vitamin D causes bone resorption and raise blood calcium levels. Low quantities of vitamin D reduce intestinal absorption and renal conservation of calcium and result in a drop in blood calcium, which stimulates PTH release. PTH stimulates bone resorption to release calcium and restore blood levels. Therefore, osteomalacia can result from both deficiency and excess of vitamin D. Elevated PTH concentrations stimulate the kidney to conserve calcium. Vitamin D toxicity can be the result of excessive dietary intake. Intestinal absorption of calcium and osteoclastic activity are increased and result in blood levels that exceed the renal capacity for excretion. This leads to deposition of calcium in soft tissue such as the aorta and kidney. Vitamin D deficiency can arise from inade- quate dietary intake of exogenous precursors, or inadequate exposure to ultraviolet light that is required for conversion of endogenous precursors. Deficiency of vitamin D results in rickets in growing animals and osteomalacia in adults. In humans, vitamin D deficiency is now recognized as a major cause of metabolic bone disease in elderly people (Holick, 1996). The role of vitamin D in calcium regulation in rabbits differs from other species. Vitamin D does not appear to play the same regula- tory role in intestinal absorption as in other mammals. Studies into chronic vitamin D deficiency in adult rabbits indicate that intestinal absorption of calcium is passive and efficient and does not require vitamin D (Bourdeau et al., 1986). However, vitamin D increases intestinal absorption of calcium and is required if dietary levels are low (Tvede- gaard, 1987; Brommage et al., 1988). In rabbits, vitamin D plays an important role in phophorus metabolism. Vitamin deficiency results in a reduction in intestinal absorption of phosphorus. Experimental studies have shown that chronic vitamin D deficiency can result in hypophosphataemia and osteomalacia (Brommage et al., 1988). Photosynthesis of vitamin D takes place in the skin of fur and fleece bearing animals such as horses and sheep, although it is absent from some carnivorous species such as cats which obtain vitamin D from prey (How et al., 1994). Sunlight is required for endoge- nous vitamin D synthesis by rabbits. Rickets can be induced in growing rabbits by keeping them in the dark or under artificial light (Kato, 1966; Curry et al., 1974). It takes approximately 5 months for serum concen- trations of 25-OH-D and 1,25(OH)2D to become undetectable in rabbits on a vitamin D deficient diet (Nyomba et al., 1984; Brommage et al., 1988). Undetectable serum concentrations of 1,25(OH)2D have been found in pet rabbits during the spring after they were confined to hutches for the winter (see Figure 2.1). Pet rabbits kept in free-range conditions with unrestricted access to natural daylight through the winter had significantly higher 1,25-(OH)2D3 concentrations (Fairham and Harcourt-Brown, 1999). Vitamin D deficiency may be a contributory factor in the develop- ment of dental disease (see Section 7.5.1.1). Vitamin D is rare in foods. Liver and animal fats are a source of vitamin D for carnivorous species but not for an obligate herbivore such as a rabbit. Instead, vitamin D must be metabolized endogenously or obtained from a dietary source such as sun- dried vegetation or a vitamin supplement. Irradiated plant sterols with anti-rachitic potency occur in the dead leaves of plants or sun-cured hays rather than in the green leaves of growing plants. Variation in the vitamin D content of hay can occur with different methods of curing. Exposure to irradiation by sunlight for long periods causes a marked increase in anti-rachitic potency of cut fodder, whereas modern hay making techniques with its emphasis on rapid curing tends to keep vitamin D levels at a minimum (Blood et al., 1979). Rabbits enjoy eating dried vegetation such as fallen tree leaves in the autumn and will often eat them in preference to grass. There is also an interaction between vitamin A and vitamin D. Vitamin A appears to intensify the severity of rickets and inhibit the ability of vitamin D to cure the disease. Vitamin A administration to rats produced a decrease in total bone ash, increased the epiphyseal bone width and 35Diet and husbandry 20–30% of the calcium is in the form of calcium oxalate that reduces its availability. In a study by Cheeke et al. (1985), 49% of the calcium in calcium oxalate was available to rabbits. Low oxalate, high calcium vegetables include kale, broccoli, turnip, collard and mustard greens (Breslau, 1996). Calcium can also bind with long-chain unsaturated fatty acids in the intestine to form insoluble soaps. Calcium absorption can be enhanced by certain dietary factors. Soluble complexes can be formed with certain amino acids such as lysine and arginine and antibiotics such as chloramphenicol and penicillin. The soluble complexes prevent the formation of insoluble complexes and therefore facilitate calcium absorption. Lactose also increases the absorp- tion of calcium from the gut (Breslau, 1996). Many ingredients of rabbit food have a low calcium content that decreases the concentra- tion gradient for passive diffusion from the gut into the blood. Vitamin D may not be available for active calcium transport across the gut wall. Undetectable vitamin D levels have been recorded in pet rabbits (Fairham and Harcourt-Brown, 1999). Calcium deficiency can be a contributory factor to poor tooth and bone quality and dental disease in pet rabbits. The selection of cereals and legumes from mixed rations results in a diet containing less in calcium than the amount required for bone calcification (Table 2.2) (Harcourt-Brown, 1995, 1996). Excessive dietary calcium may contribute to the development of urolithiasis (Kamphues et al., 1986). Therefore, the dietary level of calcium is important. The calcium requirement for rabbits has been determined (Chapin and Smith, 1967a). A minimum of 0.22% is required to support normal growth but a level of 0.44% is required for bone calci- fication. A level of 0.6–1.0% is recommended for pet rabbits (Lowe, 1998). The calcium and phosphorus content of some ingredients of rabbit food is summarized in Table 2.3. 2.13.7.2 Phosphorus Phosphorus has many physiological functions. It is closely associated with calcium and forms a major constituent of bone. Phosphorus occurs in phosphoproteins, nucleic acids and phospholipids and plays a vital role in energy metabolism. Absorption and excretion is regulated by vitamin D. Dietary phosphorus levels affect calcium absorption as calcium binds with phosphorus to form insoluble 38 Textbook of Rabbit Medicine Table 2.2 Mean calcium (Ca) and phosphorus (P) content (%) of three randomly selected brands of mixed rations sold as rabbit food Samples of rabbit food were taken from batches of mixed rations bought from the same three pet shops on three different occasions. 1 lb (0.45 kg) of food was sent for analysis. The remainder of the batch was picked over to remove the whole grain and the pellets, which are the ingredients most likely to be rejected by pet rabbits (see Figure 2.3). 1 lb (0.45 kg) of the remaining ration (without pellets and grain) was sent for analysis. Sample Food A Food A Food B Food B Food C Food C (no pellets (no pellets (no pellets or grain) or grain) or grain) 1 Ca (%) 0.70 0.26** 0.56 0.46 0.79 0.16**** P (%) 0.35 0.28 0.39 0.30 0.32 0.26 2 Ca (%) 0.63 0.28** 0.51 0.38** 0.87 0.11**** P (%) 0.41 0.34 0.39 0.32 0.36 0.27 3 Ca (%) 0.65 0.39** 0.49 0.48 0.98 0.14**** P (%) 0.41 0.29 0.39 0.32 0.36 0.29 Figures in bold denote an inverse calcium:phosphorus ratio. ** Calcium levels below the 0.4% minimum level recommended for rabbits by National Research Council (1977) Nutrient Requirements of Rabbits. **** Calcium level below the 0.22% minimum dietary requirement for rabbits determined by Chapin and Smith (1967). NB. A level of at least 0.44% calcium has been determined for maximum bone ash and bone density (Chapin and Smith, 1967). (Reprinted from Harcourt-Brown (1996) with permission from the Veterinary Record). calcium phosphate in the gut. Phytates that are found in many plants, especially grains, contain phosphorus that is released into the digestive tract of some species due to the action of ruminal or caecal fermentation. Investiga- tions have shown that phytate phosphorus is available to rabbits (Cheeke, 1987). Phytates or oxalates can bind with calcium in the gut and affect the calcium:phosphorus ratio. The avail- ability to rabbits of phosphorus in alfalfa is low (Cheeke et al., 1985). Phosphorus deficiency results in rickets in growing animals and osteomalacia in adults. In some areas the soil is deficient in phospho- rus and grazing animals show symptoms of ‘pica’ (depraved appetite) where they chew wood, bones and other foreign material. Growing parts of plants are richer in phosphorus (McDonald et al., 1996). In rabbits, dietary restriction of phosphorus causes hypophosphataemia and an increase in urinary excretion of calcium. The calcium:phosphorus ratio in the diet affects bone density. In rabbits, a low calcium: phosphorus ratio of 1:2 or 1:3 does not affect bone calcification or growth rate unless dietary phosphorus levels are high. If dietary phospho- rus concentrations increase to more than 1% 39Diet and husbandry Table 2.3 Calcium and phosphorus content of some common foods for rabbits Type of food Water Dry matter Calcium Phosphorus Calcium: High, medium or (%) (%) (% of dry (% of dry phosphorus low source of matter) matter) ratio (approx.) calcium Alfalfa 10 90 1.5 0.30 5:1 High Apple 79 21 0.06 0.06 1:1 Low Barley (grain) 11 89 0.07 0.39 1:6 Low Banana 76 24 0.03 0.11 1:36 Low Beans e.g. kidney 10 90 0.14 0.46 1:3 Low Bran 11 89 0.16 0.14 1:1 Low Bread 36 64 0.09 0.16 1:17 Low Cabbage 78 12 0.64 0.35 2:1 Moderate Carrot tops 83 17 1.94 0.19 10:1 High Carrots 88 12 0.37 0.325 1:1 Moderate Celery 94 6 0.66 0.47 1:1 Moderate Chickweed 0.8 0.6 1:1 Moderate Clover 80 20 1.4 1.30 1:1 High Dandelion 85 15 1.3 0.46 3:1 High Grass 80 205 0.50 0.37 1:1 Moderate Goosegrass 1.5 0.4 4:1 High Kale 85 15 1.60 0.50 3:1 High Lettuce 95 5 0.86 0.46 2:1 Moderate Maize 88 12 0.04 0.28 1:7 Low Oats 10 90 0.03 0.33 1:11 Low Peas 11 89 0.12 0.41 1:3 Low Pineapple 75 15 0.14 0.07 2:1 Low Shepherd’s purse 2.0 0.6 3:1 High Sunflower seeds 8 92 0.22 0.68 1:3 Low Sowthistle 1.5 0.5 3:1 High Spear thistle 1.8 0.4 4:1 High Swede 88 12 0.36 0.32 1:1 Moderate Turnip 91 9 0.56 0.28 2:1 Moderate Wheat 11 89 0.16 1.14 1:7 Low Reference sources: The Nutrient Requirements of Farm Livestock (1976) No. 4. Composition of British Feedingstuffs. Technical Review and Tables. Agricultural Research Council. London. Rabbit Feeding and Nutrition (1987) Cheeke, P. Academic Press. San Diego. Animal Nutrition 5th Edition (1995) McDonald P. et al., Longman Ltd. then bone density decreases if the calcium:phosphorus ratio falls below 1:1. Many cereals have phosphorus levels greater than 1% and a calcium:phosphorus ratio that is less than 1:1 and can therefore affect bone density. Rabbits are tolerant of a high calcium:phospho- rus ratio. Growth rate and bone density are not affected by increasing calcium concentrations to a ratio of 12:1 (Chapin and Smith, 1967b). The minimum requirement of phosphorus for optimum bone strength in growing rabbits is 0.22% (Mathieu and Smith, 1961). A nutritional requirement of phosphorus for maintenance of adult rabbits has not been determined. A dietary level of 0.4–0.8% has been suggested for pet rabbits (Lowe, 1998). The phosphorus content of grass and hay is less than 0.4% (McDonald et al., 1996). 2.13.7.3 Other minerals The nutritional requirement of magnesium, manganese, iron, zinc, copper and cobalt have been determined for rabbits. The precise role of magnesium in rabbit nutrition is largely unknown but deficiency has been linked with alopecia and alterations in fur texture. Experimentally induced magnesium deficiency results in poor growth, hyperex- citability and convulsions (Cheeke, 1987). Theoretically, excessive quantities of goitro- genic vegetables such as cabbage and brussels sprouts could result in iodine deficiency. These vegetables contain glucosinolates that convert to thiocyanate which can cause iodine deficiency and goitre. Suggested dietary levels of trace elements are given in Box 2.5. 2.14 Salt licks and mineral blocks Salt licks are sold for rabbits and are available from most pet shops. They attach to the cage bars or wire mesh. There is little evidence that additional salt is required but some rabbits like the taste. Mineral blocks are also unnec- essary as there is no need to supply extra minerals to a rabbit on a balanced diet. Some blocks contain high levels of calcium that could be harmful if the rabbit gnaws and eats them in large amounts. A rabbit confined to a hutch may destroy and eat the mineral block as a displacement activity, not because it has a need for additional minerals. 2.15 Grass and hay for pet rabbits The natural food of rabbits is pasture grass. Grass is a balanced source of vitamins, miner- als, fermentable and indigestible fibre. Rabbits have evolved to live on grass, which they find palatable and enjoyable. Ideally, pet rabbits should be given the opportunity to graze for several hours a day. If a predator- free enclosure cannot be provided, then fresh grass can be picked daily throughout the summer months to feed to pet rabbits. Clippings from the lawn mower are not suitable as they ferment rapidly. There is a small risk of transmitting parasites from wild rabbits, dogs and foxes through grass collected from contaminated pasture. Viral haemorrhagic disease vaccination is advis- able. If fresh grass is unavailable, then hay 40 Textbook of Rabbit Medicine Key points 2.4 • The correct amount of dietary calcium is important for rabbits • Rabbits teeth grow at approximately 2 mm per week and require a constant supply of calcium • Calcium deficiency results in poor mineralization of the bones and teeth. Excessive amounts of dietary calcium result in large amounts of calcium carbonate sediment in the urine, and predisposes to sludgy urine and cystitis • A minimum level of 0.44% calcium is required for bone calcification • Rabbits that select cereals and legumes from cereal mixes will be on a low calcium diet • Poor quality hay can be deficient in either calcium or vitamin D or both • Some fruit and root vegetables such as apples and carrots are deficient in calcium • Alfalfa contains a high level of calcium • Grass, weeds and hay contain the correct dietary level of calcium for rabbits • Factors such as pH, phytates, phos- phates, oxalates and fats in the intesti- nal lumen can influence calcium uptake from the gut • Phytate phosphorus is available to rabbits. legal requirements for the labelling of rabbit food that are summarized in Box 2.6. Commer- cial feeds are divided into complementary and complete diets. Complementary diets are meant to be fed as part of a diet that includes other foods, usually hay. Complete diets do not require any supplementary food items. The visual appearance of the food is impor- tant to the owner but probably not to the rabbit. The rabbit has a wide visual field that enables it to observe surrounding predators while it is eating. The visual field does not include the area below the mouth, so food selection is based on odour and tactile information from the vibrissae. Feeding recommendations for pet rabbits are summarized in Box 2.7. 2.16.1 Pelleted diets Pelleted food consists of small cylinders of ingredients that have been ground and compressed together with a binding agent. Vitamins and minerals can be incorporated into the pellet along with sweetening agents such as molasses to improve palatability. Particle size of the ingredients is important, as it affects the digestibility of the ration and its rate of passage through the digestive tract (Lang, 1981). Small particles tend to accumu- late in the caecum and lead to an increased incidence of enteritis (Sanchez et al., 1984). Pelleted diets can be complete or comple- mentary. They vary in quality. Coccidiostats are usually incorporated into the pellet to reduce the incidence of coccidiosis in inten- sive rabbit units. The actual pelleting process does not kill any oocysts that may be conta- minating the feed (Owen, 1978). The advantages of pelleted diets are that they are convenient, easy to store and do not allow the rabbit to select out certain ingredi- ents. Different formulations can be pelleted to provide diets for rabbit that are pregnant, 43Diet and husbandry Box 2.7 Feeding recommendations for pet rabbits • Introduce new foods gradually • Good quality hay or grass should be avail- able at all times, unless a complete diet is provided that specifically states that no other food is needed. Even with a complete diet, additional hay, grass or vegetables will not be harmful • Feed a wide range of green foods and vegetables every day. Fruit and succulent vegetables such as lettuce and tomatoes should be given in moderation • Follow manufacturer’s instructions when feeding proprietary rabbit food. If the rabbit does not eat all the mixture, change the diet • If possible, allow rabbits outside to exercise in natural daylight. Care is needed to prevent them escaping or being attacked by neighbours’ dogs. Rabbits can be very destructive in the garden • Feed small amounts of concentrated food, such as pellets, cereal mixes or extruded diets, only once a day and remove the bowl after a couple of hours. If there is food left in the bowl, feed less food the next day. Hay or grass is available if the rabbit feels hungry • No more than 2–3% of the rabbit’s bodyweight of cereal mixes, pelleted or extruded rations should be fed daily. Safe plants for rabbits • Grass of any type is safe, palatable and ideal for rabbits. Vaccination against viral haemorrhagic disease (VHD) is advisable due to the risk of transmission from wild rabbits • Wild plants that are safe include: agrimony, brambles, chickweed, clover, coltsfoot, cow parsnip (hogweed), dandelion, young docks, goosegrass, ground elder, ground- sel, knapweed, mallow, mayweed, plantain, raspberry, sea beet, shepherd’s purse, sow-thistle, trefoil, vetch, wild strawberry and yarrow (NB: Many of these plants are illustrated in Virginia Richard- son’s book Rabbit Nutrition) • Safe cultivated plants include: artichoke leaves, apple, beetroot, broccoli, brussels sprouts, cabbage, carrots and carrot tops, celery, cauliflower leaves, chicory, corian- der, corncobs, green beans, kale, kohl rabi, lettuce (in moderation), parsley, peapods, pear, parsnip, radish, spinach, spring greens (spring cabbage), sprout peelings, sunflow- ers plants, swedes, sweetcorn plants, turnips, watercress. Turnips and spinach should be fed occasionally (not more than once a week) due to their oxalate content • Tree leaves can be eaten by rabbits, especially from fruit trees and hazel. lactating or growing. Fibre can be incorpo- rated into the pellet but processing reduces some of its beneficial properties and tends to make the pellets friable. Pellet binders can be used to overcome this problem. Substances such as magnesium lignosulphate, which is a byproduct of the wood pulp industry, or a clay mineral binder such as sodium betonite can be used (Lang, 1981). Disadvantages of pelleted diets are their low palatability in comparison with mixed cereal rations and the owners’ perception that they look boring. As a complete diet, pellets provide little in the way of dental exercise and are not a good source of indigestible fibre. Supplementary hay is required. 2.16.2 Extruded or expanded diets Expanded diets are produced by blending and heating the raw ingredients to a high temper- ature, before being extruded and dried. The basic ingredients are ground and mixed prior to steam heating. A paste is formed that is forced through a shaped die and cooled. The result is a lightweight biscuit that can be any size or shape. It stores well and is virtually sterile. Long fibre particles can be incorpo- rated without the pellets becoming friable and disintegrating. Vitamins are partly denatured by the processing and need to be added to the initial mixture in higher quantities to allow for this. Heat treatment increases starch digestibility (Cheeke, 1987) and reduces carbo- hydrate overload of the hindgut. Extruded diets are more palatable and digestible than pelleted rations (Tobin, 1996). They do not allow the animal to eat an unbalanced diet by selecting out favourite ingredients. Although extruded pellets can be made in a variety of sizes, shapes and colours, they still look less attractive than mixed rations to the owner and do not provide high quantities of indigestible fibre. 2.16.3 Mixed rations The composition of mixed rations varies between sources. They can be complete or complementary. Most mixed rations are complementary and are designed to be fed with hay to provide indigestible fibre. Feed companies decide on the formulation accord- ing to cost, availability of ingredients and the experience of the nutritionist. Nutritional data are obtained from analysis tables and extrap- olated to formulate a feed based on the requirements of commercial rabbits. Mixed rations are often sold loose from pet shops with no labelling information. Owners are encouraged to leave a bowl full of food with the rabbit permanently. The rations usually consist of flaked, micronized or rolled cereals and legumes mixed with highly coloured extruded ‘biscuits’ and pellets. Stems of alfalfa can be incorporated as a source of calcium and fibre. The colour of the extruded portions in combination with green flaked peas and yellow flaked maize make these mixtures visually appealing to the owner. Molasses or liquid sweetening agents can be added along with other ingredients such as locust beans or compressed linseed. Some rations contain byproducts from the human food industry, such as stale breakfast cereals. Whole grains are incorporated to prevent the rabbit picking out the kernel and leaving the fibrous husk. However, most rabbits are able to separate and eat the kernel and leave the husk uneaten. Wheat has a tendency to be pasty (Lowe, 1998) and is usually extruded into a coloured biscuit that is included in mixed rations. Pellets are added to the mixture as a vehicle for a powdered vitamin and mineral supple- ment. Some brands now incorporate the supplement into the extruded wheat portion or spray the whole mixture with a supple- mented coating. The advantages of mixed rations are that they are universally available, palatable, cheap, convenient and visually attractive to the owner. They are available from pet shops, supermarkets, agricultural suppliers, garages, garden centres and wholesalers under the universal name of ‘rabbit food’. Apart from the general problems associated with feeding ad lib concentrated foods (obesity, insufficient dietary fibre, dental exercise and foraging), mixed cereal rations have the additional disadvantage of allowing rabbits to select out their favourite ingredients and leave the rest uneaten (see Figure 2.3). Discarded food is generally taken away by the owner and replaced with a fresh bowlful for the rabbit to select from. Owners worry about their pets being bored or hungry and sometimes refill 44 Textbook of Rabbit Medicine the bowl several times a day so the rabbit may exist on only one or two favourite ingre- dients. The pellets, which contain the vitamin and mineral supplement, are often left uneaten. The most palatable portions of these diets are the flaked peas and flaked maize which are deficient in calcium and have a low calcium to phosphorus ratio. Selection of these ingredients results in a diet with calcium concentrations below the rabbit’s known dietary requirement (Harcourt-Brown, 1996). Demineralization of the bones and teeth results in dental problems (see Section 7.5.1.1). A balanced diet is especially impor- tant to juvenile rabbits that are growing rapidly and therefore susceptible to metabolic bone disease. Selection of low calcium cereals and legumes from mixed rations at this stage can have life-long detrimental effects on bones and teeth. 45Diet and husbandry Figure 2.3. Selective feeding in rabbits. Results of owner questionnaire: food preference of pet rabbits. Ninety rabbit owners completed a questionnaire about the feeding habits of their pet. All the rabbits were fed on mixed rations purchased as ‘rabbit food’. Hay was offered to all the rabbits in the survey although they did not always eat it. Some rabbits were given additional vegetables or allowed to graze in a run periodically through the summer months. In nearly every case, a bowl of ‘rabbit food’ was left with the rabbit permanently. Discarded food was thrown away and the bowl topped once or twice daily. This feeding practice allowed rabbits to select their favourite food items and eat nothing else. Some rabbits existed on one or two ingredients. The low calcium cereals and peas were the rabbits’ favourite part of the ration. The pellets that contain a vitamin and mineral supplement were the least palatable part of the mixture. However, some rabbits would eat the entire mixture and a minority would select the pellets. (From Harcourt-Brown (1996), reprinted with permission from Veterinary Record). 48 Textbook of Rabbit Medicine Table 2.4 Potentially toxic plants for rabbits Rabbit owners are often concerned about the safety of feeding naturally growing plants and weeds to their rabbits. During an extensive search of the literature, few definite reports of plant toxicity in rabbits could be found although many plants were cited as potentially poisonous. There are anecdotal reports of bizarre behaviour in rabbits after presumed ingestion of some species of wild mushrooms. The following table is a list of potentially toxic plants for rabbits although in many cases, extrapolations have been made from other species. The following plants can be bought as vegetables or grow in gardens and hedgerows in the UK. Poisonous plants from other countries are not included. Plant Toxic principal Comments Amaranthus: Oxalic acid Red wheat is known to be toxic to rabbits. A. retroflexus (Red wheat) A. albus is the garden plant Love-Lies-Bleeding A. viridis (Green amaranthus) Antirrhinums Known to be poisonous in other species Arum Calcium oxalate Can cause swelling and discomfort of the oral cavity and other irritants in other species Buttercups(fresh) Protoaneminin Causes irritation to mucous membranes including GI tract in other species Bracken Thiaminase Toxic in cattle, sheep and horses + bone marrow suppressant Bryony Irritant substance Berries and rhizomes are poisonous and histamine Cabbage Glucosinolate Goitrogenic if fed in large quantities Celandines A variety of Unpalatable alkaloids Irritant effects. Purgative Charlock Poisonous in other species Comfrey Pyrrolizidine Hepatotoxic (rabbits appear to be resistant to toxic Alkaloids effects) Convolvulus Poisonous in other species Crotalaria Pyrrolizidine Hepatotoxic (rabbits appear to be resistant to toxic Alkaloids effects) Dahlia Known to be poisonous in other species Evergreens(except conifers) Known to be poisonous in other species Figwort Reputed to be poisonous Foxglove Cardiac glycoside Known to be poisonous in other species (digitalis) Hellibore Variety of alkaloids Known to be poisonous in a range of species (Christmas rose) Whole plant is toxic especially during flowering Hemlock Variety of alkaloids Whole plant is toxic Unpalatable Henbane Anticholinergic Seeds are most toxic part of the plant Unpalatable Horsetails Thiaminase Toxic to other species (horses) Alkaloids if ingested over long periods. Silica Remains toxic after drying, i.e. hay Irises Reputed to be poisonous Ivy Unidentified Whole plant, including berries poisonous Large quantities need to be ingested. Kale Thiocyanates Toxicity reported in ruminants S-methyl-cysteine- Needs to be ingested large quantities sulfoxide Nitrates Can cause haemolytic anaemia in other species Antithyroid Laburnum Alkaloids Seeds especially are known to be poisonous in other species Rabbits may be resistant to toxic compounds diseases in many species. Aflatoxin is produced by Aspergillus flavus and may be found in mouldy feeds, especially peanuts. Subclinical aflatoxicosis affects natural defence mechanisms and immunogenesis. Rabbits are susceptible to aflatoxin toxicity, which causes gastroenteritis and liver damage. It is not known how widespread this problem is in pet rabbits that consume cereals and grains of uncertain age and quality. In a study by Fekete and Huszenicza (1993), rabbits did not refuse grain that contained sufficient aflatoxin to cause immunosuppression and fatal secondary bacterial infection. References Bellier R., Gidenne T. (1996). Consequences of reduced fibre intake on digestion, rate of passage and caecal microbial activity in the young rabbit (Abstract). Br Vet J., 75, 353–363. Berthelsen, H., Hansen, L.T. (1999). The effect of hay on the behaviour of caged rabbits (Oryctolagus cuniculus) Animal Welfare, 8, 149–157. Blood, D.C., Henderson, J.A., Radostits O.M. (1979). Veterinary Medicine, 5th edn. p. 910. Balliere Tindall. Blood, D.C., Studdert, V.P. (1999). Ballieres Comprehensive Veterinary Dictionary. Balliere Tindall. Bourdeau, J.E., Shwer-Dymerski, D.A., Stern, P.A., Langman, C.B. (1986). Calcium and phosphorous metabolism in chronically vitamin D-deficient labora- tory rabbits. Miner Electrolyte Metab., 12, 176–185. 49Diet and husbandry Lily of the valley Variety of alkaloids Variety of symptoms Linseed Cyanogenetic Ingestion of > 400 g/100 kg of oil-seed cake can Heteroside be toxic in other species Lupins Quinolizidene Most cultivated lupins are of low toxicity Alkaloids Milkweed Cardiac glycoside Monkshood (aconite) Alkaloid Unpalatable, irritant Nightshade Atropine Many rabbits are resistant to poisoning due to presence of atropinesterase Oleander Cardiac glycoside Poppies Opium alkaloids Entire plant is toxic even after drying Potato plants Solanines Can cause haemolysis in other species (cattle and pigs) if large quantities of leaves or stems are fed or small quantities over a long period Potatoes Nitrophenol Potatoes may be sprayed with nitrophenols to prevent sprouting. The spray can be toxic to rabbits Privet Tannins Can be fatal in other species Heteroside Ragwort Pyrrolizidine Hepatotoxic Alkaloids Rabbits appear to be resistant to toxic effects Scarlet pimpernel Reputed to be poisonous Speedwell Reputed to be poisonous Spurges Alkaloids Cause intense local irritation to mucous membranes in other species Toadflax Reputed to be poisonous Tomato plants Solanines Can cause haemolysis in other species (cattle and pigs) if large leaves or stems are fed or small quantities over a long period Travellers joy (Clematis vitalba) Reputed to be poisonous Wild celery Reputed to be poisonous Yew Taxine Cut branches more toxic than when fresh Very toxic in other species Can cause sudden death Probably toxic to rabbits There are other toxic plants not included in this list that are wise to avoid, e.g. acorns, box hedging, laurel, cypress, verbena, potentilla, rhododendron, water dropwort. In general, plants that grow from bulbs can be considered to be potentially poisonous. Reference sources: Lang, J. (1981); Cheeke, P.R. (1987); Sandford, J. (1996); Lorgue, G. et al., (1996); Gfeller, R.W., Messonier S.P. (1998); Richardson, V. (1999). Breslau, N.A. (1996). Calcium, magnesium and phospho- rus: Intestinal absorption. In Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism. (M.J. Favus, ed.) pp 49–56. Lippincott-Raven. Brommage, R., Miller, S.C., Langman, C.B. et al. (1988). The effect of chronic Vitamin D deficiency on the skele- ton in the adult rabbit. Bone, 9, 131. Brown, S.A. (1997). Rabbit gastrointestinal physiology and disease. Proceedings of Atlantic Coast Veterinary Conference, Atlantic City. Campbell, A. (1998). Poisoning in small animals from commonly ingested plants. In Practice, 20, 587–591. Campbell, J.M., Fahey, G.C, Wolf, B.W. (1997). Selected indigestible oligosaccharides affect large bowel mass, cecal and fecal short-chain fatty acids, pH and microflora in rats (Abstract). J Nutr., 127, 130–136. Carabaõ, R., Fraga, M.J., Santoma, G., de Blas, J. (1988). Effect of diet on composition of cecal contents and on excretion and composition of soft and hard feces of rabbits. J Anim Sc., 66, 901–910. Chapin, R.E., Smith, S.E. (1967a). Calcium requirement of growing rabbits. J Anim Sci., 26, 67–71. Chapin, R.E., Smith, S.E. (1967b). The calcium tolerance of growing rabbits. Cornell Veterinarian, 57, 492. Cheeke, P.R. (1987). Rabbit Feeding and Nutrition. Acade- mic Press. Cheeke, P.R. (1994). Nutrition and nutritional diseases. In The Biology of the Laboratory Rabbit, 2nd edn. (P.J. Manning, D.H. Ringler, C.E. Newcomer, eds). pp 321–333. Academic Press. Cheeke, P.R., Amberg, J.W. (1973). Comparative calcium excretion by rats and rabbits. J Anim Sci., 37, 450. Cheeke, P.R., Patton N.M., Templeton G.S. (1982). Rabbit Production. Interstate Publishers. Cheeke, P.R., Bronson, J., Robinson, K.L., Patton N.M. (1985). Availability of calcium, phosphorus and magnesium in rabbit feeds and mineral supplements. J Appl Rabbit Res., 8, 72–74. Chiou, P.W., Yu, B., Lin, C. (1998). The effect of different fibre components on growth rate, nutrient digestibility, rate of digesta passage and hindgut fermentation in domestic rabbits. Lab Anim., 32, 276–283. Craigmill, A.L., Eide, R.N., Shultz, T.A., Hedrick, K. (1984). Toxicity of avocado (Persea americana, Guata- malan var.) leaves: Review and preliminary report. Vet Hum Toxicol., 26, 381–383. Crossley, D.A. (1995). Clinical aspects of lagomorph dental anatomy: The rabbit (Oryctolagus cuniculus). J Vet Dent., 12, 137–140. Curry, O.B., Basten, J.F., Francis, M.J.O., Smith, R. (1974). Calcium uptake by sarcoplasmic reticulum of muscle from vitamin D deficient rabbits. Nature, 249, 83–84. De Blas, E., Gidenne, T. (1998). Digestion of starch and sugars. In The Nutrition of the Rabbit. (C. de Blas and J.Wiseman, eds). pp 17–38. CABI Publishing. Drescher, B. (1993). Zusammenfassende Betrachtung über den Einflub unterscheidlicher Haltungsverfahren auf die Fitness von Versuchs- und Fleischkaninchen. Tierärzl Umschau, 48, 72–6. Drescher, B., Breig, P. (1993). Einflub unterscheidlicher Haltungs-verfahren auf die Nebennien von Kaninchen. (Article in German, English abstract). Tierärzl Umschau, 48, 30–34. Drescher, B., Loeffler, K. (1996). Scoliosis, lordosis and kyphosis in breeding rabbits. Tierärzl Prax, 24, 292–300. Fairham, J., Harcourt-Brown, F.M. (1999). Preliminary investigation of the vitamin D status of pet rabbits. Vet Rec., 145, 452–454. Fekete, S. (1989). Recent findings and future perspectives of digestive physiology in rabbits: a review. Acta Vet Hung., 37, 265–279. Fekete, S., Bokori, J. (1985). The effect of the fibre and protein level of the ration upon cecotrophy of rabbit. J Appl Rabbit Res., 8, 68–71. Fekete, S., Huszenicza, G. (1993). Effects of T-2 Toxin on ovarian activity and some metabolic variables of rabbits. Lab Anim Sci., 43, 646–649. Fitter, R., Fitter, A., Blamey, M. (1974). The Wild Flowers of Britain and Northern Europe. Collins. Fowler, M.E.,(1986). Metabolic bone disease. In Zoo and Wild Animal Medicine, 2nd edn. (M.E. Fowler, ed.) pp 69–90. W.B. Saunders. Fox, R.R., Crary, D.D. (1971). Mandibular prognathism in the rabbit. J Hered., 62, 163–169. Fox, R.R., Eaton, H.D., Crary, D.D. (1982). Vitamin A, beta carotene, and hereditary bupthalmus in the rabbit (Abstract). J Hered., 73, 370–374. Gfeller, R.W., Messonier S.P. (1998). Small Animal Toxicol- ogy and Poisonings. Mosby. Gidenne, T., Carabaõ, R., Garcia J., de Blas, C. (1998) Fibre digestion. In The Nutrition of the Rabbit. (C. de Blas and J. Wiseman, eds). pp 69–88. CABI Publishing. Greene, H.S.N. (1941). Uterine adenomata in the rabbit. J Exp Med., 73, 273–292. Harcourt-Brown, F.M. (1995). A review of clinical condi- tions in pet rabbits associated with their teeth. Vet Rec., 137, 341–346. Harcourt-Brown, F.M. (1996). Calcium deficiency, diet and dental disease in pet rabbits. Vet Rec., 139, 567–571. Harcourt-Brown, F.M., Baker, S.J. (2001). Parathyroid hormone, haematological and biochemical parameters in relation to dental disease and husbandry in pet rabbits. J Small Anim Pract., 42, 130–136. Harris, D.J., Cheeke, P.R., Patton, N.M. (1983). Feed preference studies with rabbits fed fourteen different greens. J Appl Rabbit Res., 6, 120–121. Holick, M.F. (1990). The use and interpretation of assays for Vitamin D and its metabolites. J Nutr., 120, 1464–1469. Holick, M.F. (1996). Vitamin D and bone health. J Nutr., 126, 1159S–1164S. How, K.L., Hazewinkel, H.A.W., Mol, J.A., (1994). Photo- synthesis of vitamin D3 in cats. Vet Rec., 134, 384. Huls, W.L., Brooks, D.L., Bean-Knudsen, D. (1991). Response of adult New Zealand white rabbits to enrichment objects and paired housing. Lab Anim Sci., 41, 609–612. Hunt, C.E., Harrington, D.D. (1974). Nutrition and nutri- 50 Textbook of Rabbit Medicine catecholamine release can cause heart failure and death. Stress due to overcrowding has been used to induce cardiomyopathy in laboratory rabbits (Weber and Van der Walt, 1975). Stimulation of the sympathetic nervous system inhibits activity of the gastrointestinal tract. Gut motility is reduced, which can have a knock-on effect on caecal microflora and digestive function. Enterotoxaemia or gut stasis can result from any stressful situation. Mucoid enteropathy is associated with stress- ful situations such as weaning, parturition or re-homing. Stress reduces renal blood flow in rabbits. In a study by Kaplan and Smith (1935) into the effects of diuresis and urine flow, a single dose of 50 ml/kg of water was given to rabbits before subjecting them to unpleasant or painful stimuli. The rabbits were subjected to electric shocks, loud bangs or being tied in a supine position on an animal board for long periods of time. In all cases the disturbing stimuli were immediately followed by a marked decrease in urine flow, renal plasma flow and filtration rate. Oliguria was frequently severe, lasting from 30 to 120 minutes. Some rabbits died in convulsions. 53The rabbit consultation Box 3.2 Stress in rabbits Causes of stress of rabbits • Pain and disease • Unfamiliar surroundings • Transport • Rough handling • Proximity of potential predators: dogs, cats, ferrets, birds of prey and, for wild rabbits, humans • A dominant companion and no means of escape • Inability to exhibit natural behaviour patterns, e.g. to forage, make a nest or interact socially • Poor husbandry: insufficient food, water and indigestible fibre, excessively high or low environmental temperature Effects of stress in rabbits Many of the effects of stress are linked to the release of catecholamines or corticosteroids and can be life-threatening: • Catecholamine release can cause heart failure and death. Stress due to overcrowding has been used to induce cardiomyopathy in laboratory rabbits • Stimulation of the sympathetic nervous system inhibits activity of the gastroin- testinal tract. Gut motility is reduced, which can have a knock-on effect. Gut stasis, trichobezoar formation (hairballs), enterotoxaemia and mucoid enteropathy can all be linked with stress • Stress in rabbits causes a marked decrease in urine flow, renal plasma flow and filtration rate. Oliguria can last from 30 to 120 minutes • Stress can increase gastric acidity and cause gastric ulceration in rabbits • Stress is immunosuppressive. Rabbits suffering from dental disease have signifi- cantly lower lymphocyte counts than healthy rabbits • Stress affects carbohydrate metabolism. Handling alone can cause an increase in blood glucose to the order of 8.5 mmol/l. Blood glucose levels can be very high (20–25 mmol/l) in association with intesti- nal obstruction and other stressful diseases • Stress causes anorexia that, in combina- tion with disruption to normal carbohy- drate metabolism, can lead to hepatic lipidosis, liver failure and death Ways to minimize stress in rabbits undergoing veterinary treatment • Use analgesics in any situation where the rabbit may be experiencing pain • Use quiet, gentle handling and sedate or anaesthetize rabbits for painful or uncom- fortable procedures • Wrap rabbits in a towel for examination or procedures such as blood sampling • Keep rabbits away from the sight, sound and smell of predators, e.g. barking dogs, ferrets • Provide hay as bedding material for rabbits awaiting or recovering from surgery. Hay smells familiar and provides security for timid animals. It is also a source of indigestible fibre and foraging material • Consider hospitalizing a bonded compan- ion with a sick rabbit • Minimize stressful procedures or devices, e.g. Elizabethan collars or nasogastric tubes The control group of rabbits that were not stimulated and remained undisturbed could withstand diuresis by increasing urine flow. Stress increases gastric acidity. Gastric ulcers are a common post-mortem finding in rabbits, especially in those that have been anorexic prior to death. In a survey of 1000 post-mortem examinations by Hinton (1980), 7.3% were found to have ulceration of the gastric mucosa that was related to the stress of the associated illness. Experimental stress ulcers have been induced in the gastric mucosa of laboratory rabbits by administer- ing intraperitoneal injections of adrenaline (Behara et al., 1980). Stress can alter the differential white cell count in any species. Rabbits are particularly susceptible to the effects of stress. A car journey to the surgery, a period in the waiting room next to a barking dog or the excitement of handling can be reflected in the blood picture. Adrenaline and cortisol affect the distribution of lymphocytes throughout the body. Administration of exogenous adrena- line to rabbits results in redistribution of lymphocytes from spleen and bone marrow to peripheral blood, lungs and liver (Toft et al., 1992a). Conversely, exogenous corticos- teroid administration results in a redistribu- tion of lymphocytes from the peripheral blood, bone marrow and spleen to the lymphatic tissue in rabbits (Toft et al., 1992b). Prolonged periods of stress cause lymphopae- nia. Rabbits suffering from clinical symptoms of dental disease have significantly lower lymphocyte counts than healthy rabbits kept under free-range conditions (Harcourt-Brown and Baker, 2001) (see Figure 6.1). Carbohydrate metabolism is affected by stress. Handling alone can cause an increase in blood glucose to the order of 8.5 mmol/l. Blood glucose levels can rise to 20–25 mmol/l in critically ill rabbits, such as those with an intestinal obstruction. Disruptions in carbo- hydrate metabolism have potentially serious knock-on effects that can result in hepatic lipidosis, liver failure and death. As a prey species, rabbits have many physi- ological and behavioural responses to adrenal hormones. The response to danger is either to ‘freeze’ or to jump and flee. Although the majority of pet rabbits are used to being handled by their owners and are not particu- larly stressed by clinical examination, there is always potential for them to suddenly spring up and attempt to escape. Broken bones or fractured teeth can be the consequence of a leap off the consulting table. Struggling rabbits can inflict injury by scratching with the hind legs or, very occasionally, biting. Owners are often unaware of the stressful effect or the physical danger that is posed to their rabbit if it is sitting on their knee in full view of other animals in the waiting room. They may be next to potential predators such as ferrets, dogs, cats or birds of prey. Even the sound or smell of predators such as ferrets can be stressful. Loud noises, unfamiliar surroundings and car journeys all add to the stress levels of rabbits that are visiting the surgery. The effects of stress can be minimized by encouraging owners to leave their rabbits in the carrier in the waiting room, quiet gentle handling in the consulting room and the routine use of analgesics to all animals that may be in pain. 3.1.2 Reproduction Rabbits are induced ovulators without a defined oestrus cycle, although females vary in sexual receptivity and a cyclic rhythm exists (see Section 1.4). Full sexual receptivity occurs every 18 days and is manifested by restlessness and increased chin rubbing. Does are fertile immediately after kindling, especially during the summer months. Breed- ers usually take females to the buck for mating rather than vice versa as they can be territorial and attack the buck if he is put in her hutch. Sometimes the two are introduced 54 Textbook of Rabbit Medicine Key points 3.1 • Rabbits are a prey species and suscep- tible to the effects of adrenal hormones. Stress can allow the flare up of latent infections and cause gastrointestinal hypomotility, reduce renal blood flow and increase gastric acidity • Pain, unfamiliar surroundings, loud noises and the proximity of predators can stress rabbits that are brought to a veterinary surgery • The effects of stress can be minimized by gentle handling and routine use of analgesics. on neutral territory. In general, females are mated for the first time at approximately 5 months old and are not bred from over the age of 3 years (Sandford, 1996). Mating takes place within a few minutes and can be accom- panied by a scream from either party, which is deemed to be normal. Mating may be repeated after a couple of hours to improve the conception rate. Artificial insemination is a recognized technique in rabbit breeding. Pregnancy can be detected by abdominal palpation. The best time for pregnancy diagnosis is 10–14 days after mating when the fetal units can be felt as olive-sized masses. Fetal resorption can take place up to 20 days post-coitus. Mammary development occurs in late pregnancy. Radiographically, pregnancy can be detected after the 11th day. Gestation takes 31–32 days. Some does remain sexually receptive during pregnancy and will continue to be mated by a male companion. During late pregnancy the doe may be seen carrying bedding material into her chosen nesting site. The nest is built from hay, straw or other bedding material. The quality of the nest varies between individual does and has a strong influence on the survival of the young. The doe will defend her chosen nesting site against potential intruders, especially if she is pregnant or lactating and can become aggressive towards owners, other rabbits or pets. Hair is pulled from the hip, dewlap and mammary glands to line the nest. She may consume less food at this point and should be tempted to eat, as pregnancy toxaemia is a risk during this period. Other- wise, the doe should be left undisturbed. Parturition usually takes place in the morning and lasts less than 30 minutes. When the entire litter has been born, the doe pulls more fur from her body to cover the litter in its nest. Does are particularly susceptible to distur- bance in the first few days after parturition and may cannibalize the young. Inexperi- enced does sometimes mutilate them. The legs or ears may be attacked or the skin stripped over the neck, thorax or abdomen. Cannibal- ization and mutilation are most likely to take place on the day of parturition and may be an extension of eating the placenta. Sometimes young rabbits are born outside the nest or the doe rejects them. These kits will die from hypothermia unless they are warmed up and returned to the nest. The doe will usually accept them and the chances of survival are far greater if the kit is reared by its natural mother rather than being hand-reared by a human. It is advisable to remove other rabbits from the hutch during late pregnancy. Female companions can cannibalize the young and entire males will mate the doe within hours of her giving birth. Females can lactate and be pregnant at the same time and have a second litter within a few weeks of the first. The doe only feeds the young once or twice daily taking 3–5 minutes (see Section 1.4.). Owners often think the young have been deserted and need reassurance that it is normal for the mother to be out of the nest and that she may be particularly aggressive and protective during this period. Lactation takes place for approximately 5 weeks after parturition. Baby rabbits are suckled once or occasion- ally twice daily by a mother and she spends very little time with them. In the wild, although the doe remains in close vicinity of the nest, she does not groom the young or keep them warm. Nests are hidden, well insulated and secure. The babies drink suffi- cient milk in 2–5 minutes to last 24 h. It is possible for baby rabbits to survive for more than 24-h intervals between feeds, which explains why females can rear litters that exceed their number of nipples (Lang, 1981). Suckling normally takes place in the early morning and, if the doe does return to the nest to feed the young for a second time, then it is usually in the first few days after giving birth. The baby rabbits spend most of the day buried in the warmest part of the nest, tightly grouped together conserving heat and energy. After about 22 h, the whole group becomes active and makes its way to the surface (McBride, 1988). When the mother arrives, she stands over the babies which suckle, changing nipples and position approximately every 30 seconds. After about 3 minutes, the doe leaves the nest and the babies urinate on the surface before digging themselves deep into the bedding to sleep for another 22 h. Young rabbits are totally depen- dent on milk until day 10. They are usually eating small amounts of solid food by day 15 (Kraus et al., 1984) and start to leave the nest and be weaned at about 3 weeks of age. The glucose reserve of neonatal rabbits lasts approximately 6 h post partum. Hypoglycaemia results in rapid ketosis and 55The rabbit consultation the ring. These rings should be removed as they serve no purpose in the pet rabbit and can trap hair and debris beneath them. Skin necro- sis and secondary infection can set in (see Plate 1). In severe cases, the blood supply to the foot is cut off so the leg becomes gangrenous and has to be amputated or the rabbit euthanased. If the rings are not removed, owners must be advised to check them daily. Ring removal is almost impossible in the conscious animal. Sedation or general anaes- thesia is required because leg rings cannot be slipped over the hock and need to be cut. Part of a wooden tongue depressor can be slipped between the ring and the leg to keep the fur our of the way and give some protection to the skin before removing the ring with a hack saw or small saw attachment on a power drill. Care is required to prevent the metal ring from overheating. Cotton wool soaked in water can be used periodically to cool the ring during removal. 3.2 Vaccination 3.2.1 Myxomatosis vaccination Myxomatosis is a common disease in wild rabbits that can be spread to pet rabbits via insect vectors such as fleas and mosquitoes (see Section 16.6.1.). Those rabbits that are kept in gardens visited by wild rabbits are most at risk. At the present time there is only one type of vaccine available in the UK for the immunization of rabbits against myxomatosis (Nobivac Myxo, Intervet). Live vaccine is prepared from attenuated Shope fibroma virus grown on cell line culture. Shope fibroma virus naturally affects the cottontail rabbit Sylvilagus floridanus that is native to North America. It is antigenically related to myxoma virus and cross-immunity occurs. Shope fibroma virus is transmissible to the European rabbit Oryctolagus cuniculus in which it produces localized benign fibromas. In order to stimulate an antigenic reaction and afford immunity, 1 ml of the vaccine is split between two routes; 0.9 ml is adminis- tered subcutaneously and the remaining 0.1 ml is given intradermally. Intradermal immunization produces maximum antibody response due to the presence of Langerhans cells within the dermis that act as antigen- presenting cells and increase the activation of T-helper cells. The intradermal route also provides some protection for the antigen by minimizing diffusion into the surrounding tissues and providing a depot effect. The dermis has excellent lymphatic drainage and intradermal injection maximizes exposure of immune cells to the antigen and the subse- quent antibody response (Stills, 1994). The manufacturers recommend using the skin at the base of the ear for the intradermal injection and either administering the remain- der of the vaccine subcutaneously at that site or through a separate injection in the scruff. It is also possible to administer both the subcutaneous and intradermal dose through a single injection in the scruff of the neck. The 1 ml dose is drawn into a syringe with a small (23–5 g) needle attached; 0.9 ml is injected into the subcutaneous tissue. The needle, orientated with the bevel up, is then slowly advanced into the overlying dermis and the remaining 0.1 ml injected into the dermis from underneath. A bleb of vaccine can be felt forming in the dermis if the skin over the end of the needle is pinched between the thumb and forefinger as the injection is made. The vaccine can be given to rabbits over 6 weeks of age. It should not be given during pregnancy. Annual boosters are necessary, although in high-risk situations where pet rabbits are potentially exposed to insects or wild rabbits infected with myxomatosis, the interval between vaccinations can be reduced to 6 months. Myxomatosis tends to be a seasonal disease with outbreaks occurring in the late summer. The optimal time for vacci- nation is in the late spring to provide good immunity during the summer months. Insect control will also reduce the risk of infection. 3.2.2 Viral haemorrhagic disease Viral haemorrhagic disease (VHD) is a highly infectious lethal disease of rabbits. It is caused by a host-specific calicivirus (see Section 16.6.2.). VHD virus is spread by oral, nasal and parenteral transmission and is present in urine and faeces from infected rabbits. The virus can survive for long periods outside the host. It is thought that wild birds carried infection across the channel from Europe to 58 Textbook of Rabbit Medicine wild rabbits in this country. VHD may be transmitted directly from contact with wild rabbits or carried on footwear and clothing. Contaminated foods, such as grass or weeds picked from areas grazed by wild rabbits, can be a source of infection. Hutches and cages that have been occupied by an infected rabbit require thorough disinfection before a new rabbit is introduced. Ideally, only vaccinated animals should be brought in to infected premises. VHD virus can survive outside the host for 10–19 months at room temperature. Exposure to 2% Virkon for 2 h does not inacti- vate the virus, although 4% Virkon is effec- tive; 1% sodium hydroxide or 10% household bleach are also effective disinfectants (Gorski et al., 1994; Goodly, 2001). There is a vaccine against viral haemor- rhagic disease that is available in the UK (Cylap, Fort Dodge). Rabbits over 10 weeks can be vaccinated with a single dose. It is safe to vaccinate pregnant animals with VHD vaccine. Boosters are given annually. In contrast with myxomatosis vaccine the whole 1 ml dose should be given subcuta- neously. Inadvertent intradermal injection can result in tissue reaction. After subcutaneous administration, it is advisable to massage the vaccination area thoroughly and advise the owner to do the same periodically over the next few hours. In this manner, the vaccine is dispersed in the subcutaneous tissues and is less likely to cause a reaction. Some judges penalize show rabbits that have an area of dermatitis or a scar, so it is important to make sure the owners are aware of the risk. Accord- ing to the datasheet, accidental self-injection with the vaccine can cause a severe reaction in humans that could result in the loss of a finger. 3.2.3 Simultaneous administration of myxomatosis and VHD vaccine It is tempting to administer both the myxomato- sis and VHD vaccines during a single consulta- tion. There are data to support the efficacy of simultaneous vaccination but no firm conclu- sions can be drawn because of differences in the type of vaccine. During an outbreak of VHD, 5000 rabbits in Poland were simultaneously vaccinated with myxomatosis vaccine (Myxovac M) and VHD vaccine (Cunivac) without complications. Controlled exposure to infection in the laboratory suggested that rabbits that were simultaneously vaccinated were immune to both diseases (Gorski et al., 1994). However, the manufacturers of the current VHD vaccine in the UK (Cylap, Fort Dodge) have pointed out that their vaccine is different from Cunivac so no conclusions can be drawn from the Polish experience. At the present time, the manufacturers of both the myxomatosis and the VHD vaccine advise against simultaneous immunization. It is common practice to leave 2 weeks between the two injections. 3.3 Behaviour problems and aggression Like other species, rabbits respond to handling from an early age. A rabbit that associates humans with pleasurable experi- ences is less likely to be timid, scared or aggressive than a rabbit that is left to its own devices for most of the time and is chased or handled roughly when it does have human contact. A study into the effect of early 59The rabbit consultation Key points 3.3 • Pet rabbits in the UK can be vaccinated against both myxomatosis and viral haemorrhagic disease (VHD) • Myxomatosis vaccine can be given to rabbits over 6 weeks of age. VHD vaccine is given to rabbits over 10 weeks of age • Myxomatosis vaccine should not be given to pregnant does. VHD vaccine can be given during pregnancy • Myxomatosis vaccine is given subcuta- neously and a small amount (0.1 ml) intradermally • VHD vaccine must be given entirely subcutaneously and dispersed by massaging the injection area thoroughly • It is not advisable to administer both myxomatosis and VHD vaccine at the same time. At least 2 weeks should elapse between vaccinations • Myxomatosis vaccine administered during late spring offers protection over the summer months when the disease is prevalent in wild rabbits. handling has suggested that baby rabbits that are picked up and handled between the ages of 26 and 42 days are more willing to approach humans and will remain closer to them (Der Weduwen and McBride, 1999). Owners frequently seek advice about aggres- sive tendencies in their rabbits. Sometimes the reason for the aggression is obvious. Two entire males that are kept together are likely to fight and will need to be separated or castrated. Female rabbits are strongly influenced by their hormones and will vigorously defend their ‘nesting site’, i.e. a hutch or a run, and attack intruders, including other rabbits and humans. These rabbits may be quite docile when they are out of their hutch. For this reason, it is advisable to clean out hutches when they are unoccupied. Spaying usually cures this type of aggression, although it may take some weeks to settle down. Female rabbits can vigorously protect their young and aggressive behaviour can be extended to include the protection of a bonded companion. Straightforward aggression is not the only reason for rabbits biting their owners. Occasion- ally fingers are mistaken for food especially if the fingers smell of sweets or biscuits. Overzeal- ous grooming can result in a nibbling response. Young rabbits nibble objects as part of their development and can extend this exploratory behaviour to include their owners. People that smell of other rabbits or animals can be attacked as part of defensive territorial behaviour. In general it is preferable to approach nervous or aggressive rabbits from above. A rabbit that showed periodic aggression following periods of ‘stargazing’ was found to be seropositive for Encephalitozoon cuniculi (Harcourt-Brown, unpublished observation). As in other species, pain can result in aggressive behaviour. A rabbit that is normally docile but starts to be aggressive should be examined carefully for a source of pain. Dental disease and the formation of sharp hooks on the molars can be extremely painful. Rabbits are also prone to painful musculoskeletal disorders such as arthritis or vertebral spondylitis. Deafness has been reported as a cause of aggression in rabbits (Rabbit Health News 1991, 1993). Deaf rabbits may be startled by owners coming up on them unexpectedly and sometimes their response is to bite. Deafness can be caused by Psoroptes cuniculi infestation occluding the external auditory canal with mites and exudate. Many lop eared rabbits have external ear canals full of wax and debris anyway. In some rabbits, the tympanic bullae are of inspissated pus as a result of ascending Pasteurella multocida infection from the nasal cavity. Inspissated pus in the horizontal ear canal is a common post-mortem finding in many pet rabbits. Granulomatous encephalitis caused by Encephalitozoon cuniculi could cause deafness (see Section 12.4.). 3.4 Obesity Rabbits are animals that convert food efficiently and are often overfed by indulgent 60 Textbook of Rabbit Medicine Key points 3.4 • Aggression in rabbits may be hormonal, territorial or a response to pain or alarm • Obese rabbits have high resting heart rates and can develop hypertension and cardiac hypertrophy. They are prone to developing fatal hepatic lipidosis if they become anorexic • High fibre diets that would result in weight loss in other species may not be effective in rabbits. Fibre is fermented by the caecal microflora to volatile fatty acids • Weight reduction can only be achieved in rabbits by providing a diet low in digestible fibre and high in indigestible fibre • Increased amounts of exercise are an important part of a weight reduction programme • There are no serious zoonotic diseases that can be spread from rabbits to healthy humans. Immunocompromised AIDS patients may contract Encephali- tozoon cuniculi. Ringworm and ectopar- asites such as fleas or Cheyletiella parasitovorax can cause skin lesions in humans • There are many techniques for handling rabbits. Wrapping them in a towel is an effective method of restraint • The immobility response (hypnosis) can be used as restraint for minor proce- dures but is not an alternative to either anaesthesia or analgesia • The immobility response can be initi- ated by placing rabbits on their back. state. The exact role of endogenous opioid systems is controversial and there are conflicting reports about the effects of nalox- one which, theoretically, should prevent or reverse the hypnotic state (Danneman et al., 1988). Sudden noise or painful stimuli can interrupt the trance and there is considerable variation in individual susceptibility to the technique. In a study by Danneman et al. (1988), the immobility response could not be evoked in 25% of rabbits. In the consulting room, some pet rabbits can be calmed and restrained by placing them in dorsal or lateral recumbency and gently stroking their stomach while speaking to them quietly. Blowing gently on their face or stroking the bridge of the nose can also be effective. 3.8 Clinical history It is not always easy to elicit an accurate case history. Owners have preconceived ideas of the correct or incorrect way of keeping rabbits and will often wish to give the ‘right’ answer rather than a truthful one. For example, owners do not like to admit that the rabbit has not been out of its hutch for months or that it is weeks since they cleaned out its cage. When an owner says they feed ‘lots of greens’, this can mean half a cabbage leaf once a week or a diet exclusively of hay and vegetables. Misleading information can be given in response to enquiries about the amount of grass a rabbit eats. There seems to be reluctance on the part of owners to pick grass to feed to rabbits although they may be willing to put them out in a run on the lawn to graze. The length of time that a rabbit has access to grass varies considerably, from a couple of hours on two or three occasions during the summer months to several hours a day all year round. Owners often insist that their rabbit will not eat fresh greens, grass and weeds. Because the owner’s perception is that the rabbit will not eat such food, they do not offer it. It is interesting how many hospi- talized rabbits readily eat grass and dande- lions despite their owner’s protestations that their pet would not eat such a diet at home. Recent changes in husbandry can be relevant. For example, a rabbit may not have learnt to use a new automatic drinker. A new batch of food may be unpalatable. Loss of a companion can result in anorexia and depres- sion. Weight loss can result from bullying by a new dominant cage mate that prevents access to food. Owners may describe symptoms such as tooth grinding or a change in demeanour. Some rabbits exhibit low grade neurological disorders such as head nodding when they are relaxed or appear unaware of loud noises. These behavioural clues are unlikely to take place in the consulting room when the rabbit is apprehensive and have to be elicited from the owner. 3.8.1 Breed incidence Dwarf breeds appear to be predisposed to developing incisor malocclusion. Giant breeds are more susceptible to cardiomyopa- thy and arthritic conditions. The giant English and French Lops are prone to superficial pyoderma in the large skin folds that can develop under the chin and around the perineum. Entropion also occurs in these breeds. The thin fur on the hocks of Rex rabbits makes them susceptible to developing sore hocks and the short maxilla and ‘squashed in’ face of the Netherland Dwarf can alter the anatomy of the nasolacrimal duct so it is prone to blockage. Dwarf breeds appear to have a susceptibility to developing torticollis due to Encephalitozoon cuniculi infec- tion (Kunstyr and Naumann, 1983). 3.8.2 Age Young rabbits that are newly purchased are more likely to be affected by infectious diseases than the adult rabbit kept on its own. Newly weaned rabbits are susceptible to various enteric conditions. Colibacillosis is more prevalent in suckling rabbits and hepatic coccidiosis and mucoid enteropathy are most likely to occur in the post-weaning period. Stress predisposes young rabbits to pasteurel- losis. Rhinitis is often seen in young rabbits that have been taken from breeding colonies and exposed for sale in a pet shop. Congenital malocclusion is seen in the young rabbit, whereas the incidence of acquired dental disease, neoplasia and musculoskeletal problems increases with age. Thymomas and 63The rabbit consultation a variety of skin tumours are among the other types of neoplasms that have been reported in rabbits. Although tumours are usually encoun- tered in elderly patients, it is possible to discover neoplasms in young animals. Lymphosarcoma has been reported in an 8–10- week-old rabbit (Cloyd and Johnson, 1978). 3.8.3 Husbandry It is important to find out if the rabbit lives on its own or with a mate. Fur chewing or fights can result in alopecia, wounds or abscesses. Does that are kept with other does or neutered males are more likely to suffer from false pregnancies than those that are housed on their own. Contact with wild rabbits is also a relevant part of the history. It is not unknown for does to dig out of their enclosure, escape and return or be found a few days later. Myxomatosis or pregnancy can be the result. Rabbits kept in enclosures or hutches can be visited by wild rabbits, especially during the night. There is often a pile of droppings as evidence of the visit. House rabbits are prone to chewing house- hold fixtures. Heavy metal toxicity or electro- cution is more likely to occur in a house rabbit than one kept in a hutch outside. They are also at a greater risk of traumatic injuries and fractures. The material that is used in the litter tray is also an important part of the history. For example, pine shavings can cause hepatotoxicity or clay materials can cause caecal impactions. Hutch rabbits are more likely to suffer from diseases of neglect. It is not uncommon for hutch rabbits with long-standing conditions such as large abscesses, advanced dental disease, and terminal neoplasia to be presented with no clinical history at all. Hutches kept in stuffy sheds predispose to pasteurellosis and upper respiratory tract infections. Hutches exposed to severe weather conditions predis- pose to heat stroke or stress-related diseases such as gastric stasis following predator attack, a thunderstorm or severe frost. 3.8.4 Eating and drinking Rabbits normally drink 50–100 ml/kg/24 h (Brewer and Cruise, 1994). The composition and water content of the diet affects this quantity. Rabbits that eat fresh greens may not drink at all (Cheeke, 1987). High protein diets require a high water intake. Fibrous, dry foods absorb water in the intestinal tract and therefore increase thirst. During periods of water deprivation, food intake is reduced, sometimes to the point of anorexia. Conversely, food deprivation results in an increase in thirst with rabbits drinking up to 650% more water (Brewer and Cruise, 1994). Some rabbits never learn to use automatic drinkers and will only drink out of a bowl. Water deprivation eventually leads to dehydration and prerenal azotaemia. 3.8.5 Urination and defaecation Many owners do not know whether their rabbit is urinating or defaecating normally, especially if it is kept in a hutch or lives with another rabbit. Faecal consistency, size and output are an important part of the clinical history. Sometimes there are some faecal pellets in the carrier that can be examined during the consultation. A healthy rabbit, that is eating well, passes large quantities of hard faeces and eats the soft caecotrophs (see Table 3.1). The number of hard faeces varies with the fibre content of the diet. A healthy 2.5–3 kg rabbit produces about 150 hard faecal pellets a day (Lowe, 1998). Hard pellets can be expelled at any time but are always produced overnight. Absence of hard faeces is indicative of anorexia or reduced intestinal motility. Small faecal pellets are produced following periods of reduced food intake. Observant owners may see their rabbit ingesting caecotrophs from the anus. Uneaten caecotrophs are sometimes seen as shiny clusters of dark pasty pellets in the bedding of normal animals. Uneaten caecotrophs are often interpreted as diarrhoea. This is not surprising as caecotrophs have a strong smell and a soft consistency in comparison with the hard faecal pellets. Obesity, spinal problems and dental disease are among the many reasons for caecotrophs to be left uneaten (see Figure 10.6). Uneaten caecotrophs can become entangled in the fur under the tail and form an unpleasant, malodorous faecal mass. Changes in the consistency of caecotrophs can follow ingestion of a new food or a succulent 64 Textbook of Rabbit Medicine item such as lettuce or fruit. Soft, sticky or liquid caecotrophs may be passed. It is thought that this is due to alterations in the caecal microflora. Rabbits on a high fibre diet have a healthy caecal microflora that can withstand dietary changes. Uneaten caecotrophs are not life threatening although they are unpleasant for the owner and rabbit, and predispose to other conditions such as superficial pyoderma, fly strike and problems with urination due to inflamed painful perineal skin (see Sections 9.7.2, 10.6, and 14.4.3). Enteritis is signified by excretion of faecal material that cannot be identified as either hard or soft faeces. Microscopic examination of the faecal material can be helpful (see Section 6.8). Caecotrophs consist of a paste that is rich in bacteria that are easily seen on a faecal smear stained with gram’s stain. Hard faeces consist of particles of indigestible fibre and little else. Sometimes it is necessary to hospitalize the rabbit to observe faecal output. Urination should take place with no pain or discomfort. Normal rabbit urine varies considerably in its visual appearance. The colour can vary from the pale yellow colour that is familiar in other species through a range of oranges and brown to a deep red that can be mistaken for blood. The colour depends on the diet and is the result of the excretion of plant pigments. Vegetables such as cabbage, broccoli and dandelions often result in the excretion of red urine. There are clinical conditions such as urolithiasis and uterine disorders that will cause haematuria. Examination of the urine with a dipstick differentiates between blood and plant pigments. Alternatively, a Wood’s lamp can be used as urinary pigments fluoresce when exposed to ultraviolet light (Benson and Paul- Murphy, 1999). Normal rabbit urine can be cloudy due to the presence of calcium carbonate precipi- tates. The rabbit kidney is adapted for the excretion of large amounts of calcium (see Section 1.6.7). Intestinal absorption is related to the calcium content of the diet and excess amounts are excreted by the kidney. There- fore the amount of calcium carbonate precip- itate varies with the calcium content of the diet. The hydration status of the animal and pH of the urine also affect the amount of precipitate. The urine can be clear during periods of high calcium demand such as growth, pregnancy or lactation. A small amount of precipitate is a good sign as it reflects adequate calcium content in the diet. Excessive precipitate can form a thick sludge, especially in the bladder of rabbits that do not urinate frequently (see Section 14.4). High dietary calcium levels exacerbate the problem. Cystitis and urinary incontinence can be the result. It can be difficult to differ- entiate between normal calcium carbonate deposits and abnormal amounts of sludge. Normal rabbit urine is often radiopaque. Calcium carbonate deposits in the urine of an otherwise healthy animal with no sign of 65The rabbit consultation Table 3.1 Significance of faecal output Clinical condition Hard faeces Soft faeces (caecotrophs) Normal Anorexia or starvation Gut stasis Enteritis Uneaten caecotrophs Soft uneaten caecotrophs Large numbers (~150) of hard pellets produced each day Microscopically consist of strands of undigested fibre Reduced in number and size Absent Soft or liquid Normal, i.e. produced in large quantities Normal Usually not seen, although occasional cluster of caecotrophs in the bedding is not abnormal Microscopically contain an abundance of bacteria, protozoa and occasional yeast Not seen Not seen (absent) Soft or liquid. Cannot be differentiated from hard faeces May be seen as clusters in bedding or entangled in fur under tail Periodic expulsion of soft, faecal paste which easily becomes entangled in fur under the tail 68 Textbook of Rabbit Medicine Table 3.2 List of differential diagnoses for some common conditions in pet rabbits Symptoms Differential diagnosis Comments Deafness Diarrhoea (see Table 10.2) Exophthalmos: bilateral Exophthalmos: unilateral Haematuria Head tilt Increased respiratory rate Conjunctival foreign body Uveitis Entropion Swollen eyelids Middle ear infection Encephalitozoon cuniculi encephalitis Pus, wax and exudate in external ear canal Uneaten caecotrophs Uneaten soft caecotrophs Antibiotic-associated diarrhoea Enteritis Enterotoxaemia Coccidiosis Fear Males in breeding season Natural appearance Paraneoplastic disease Bilateral glaucoma Bilateral retrobulbar abscesses Glaucoma Retrobulbar disease Cystitis (‘sludgy urine’) Urolithiasis Uterine adenocarcinomas Uterine polyps Endometrial venous aneurysms Chronic polypoid cystitis, renal infarcts and disseminated intravascular coagulopathy have also been described as causes of haematuria in laboratory rabbits Encephalitozoon cuniculi Infection of the vestibular apparatus Other CNS disease (In US) Baylisascaris larva Stress Metabolic acidosis Heat stroke ? hay seeds May be congenital or acquired from fight wounds involving eyelids Myxomatosis Treponema cuniculi Neoplasia Abscesses Pus in tympanic bulla as a result of ascending infection from the eustachian tube Uneaten caecotrophs are often interpreted by owners as ‘diarrhoea’ Soft uneaten caecotrophs can be induced by dietary change, especially after introduction of succulent foods such as lettuce Some antibiotics, e.g. oral penicillin, ampicillins, clindamycin and lincomycin can induce diarrhoea by their effects on the gut flora e.g. short nosed Dwarf breeds Thymoma Congenital Secondary to other diseases such as trauma, tumours or E. cuniculi lens rupture Abscess Tumour Haemorrhage Tapeworm cyst Iatrogenic rupture of nasolacrimal duct and infiltration of periorbital space with fluid NB Blood from the uterus may be voided in urine as the vaginal vestibule fills with urine during micturition. Blood clots may be present Granulomatous inflammation of central nervous tissue Usually ascending Pasteurella multocida from nasal cavity via eustachian tube May be abscesses along vestibular tract Trauma, neoplasia, etc. Raccoons are natural host Due to unfamiliar surroundings or proximity of predators Ketoacidosis Hot stuffy shed Transport by car Hutch situated in sun continued 69The rabbit consultation Table 3.2 List of differential diagnoses for some common conditions in pet rabbits Symptoms Differential diagnosis Comments Liver disease Polydypsia Paresis/paralysis Pruritus Renal disease. NB Asymptomatic renal disease can be present due to benign embryonal nephroma, Trauma Rhinitis Obstruction of nasopharynx, larynx or trachea Lung disease Pulmonary oedema Pleural effusion Congestive heart failure Hepatic lipidosis Hepatic coccidiosis Viral haemorrhagic disease Hepatopathy Neoplasia Bile duct obstruction Toxoplasma gondii Anorexia Food deprivation Renal disease ? Diabetes mellitus Spinal fracture Degenerative disc disease Spinal deformities Neoplasia Spinal abscess ‘Floppy rabbit syndrome’ Flea infestation Louse infestation Allergic skin disease Compulsive self-mutilation Ringworm Nephrolithiasis E. cuniculi Hydronephrosis Renal calcification Heatpads ? predator attack Penetrating injuries of chest wall Haemothorax, pneomothorax, etc. Pasteurellosis Nasal foreign body, e.g. hay or seed Tooth root abscess Inflammation caused by pasteurellosis Abscess Foreign body, hay or seed Exudate from lung disease Primary bacterial pneumonia, e.g. pasteurellosis Secondary pneumonia, e.g. myxomatosis, mucoid enteropathy Viral haemorrhagic disease Aspiration pneumonia Primary or secondary neoplasia Pulmonary abscess Congestive heart failure Heat stroke Electrocution Neoplasia Cardiomyopathy Coronavirus Has been associated with pine wood shavings as litter material Aflatoxin Cysticercus pisiformis ? Neoplasia Adhesions ? E. cuniculi There is debate about incidence of diabetes mellitus in pet rabbits Trauma ? predator attack Spontaneous due to pre-existing bone disease Disc protrusion may follow trauma Kyphosis, scoliosis, spondylosis Primary or secondary bone tumours can cause spinal cord compression Spinal abscess can cause cord compression Usually dog or cat fleas continued 70 Textbook of Rabbit Medicine Table 3.2 List of differential diagnoses for some common conditions in pet rabbits Symptoms Differential diagnosis Comments congenital renal cysts or encephalitozoonisis Reversible azotaemia can occur due to stress, dehydration or water deprivation Seizures Skin lesions: alopecia Skin lesions: crusty Skin lesions : nodules Skin lesions: swellings Sudden death Weight loss (see also anorexia) Renal abscesses Staphylococcal nephritis Pyelonephritis Lymphoma Neoplasia Amyloidosis Renal agenesis Toxic compounds Encephalitozoonisis Viral haemorrhagic disease Toxicity, e.g. lead Terminal hepatic lipidosis Arteriosclerosis Toxoplasma Idiopathic epilepsy CNS disease Physiological, moulting Fur pulling for nestmaking Treponema cuniculi Barbering Fighting Cheyletiellosis Ringworm Nutritional Ringworm Superficial pyoderma secondary to trauma Ectopic Psoroptes cuniculi Allergic dermatitis Atypical myxomatosis Treponema cuniculi Rectoanal papilloma Primary tumours Circumscribed abscesses Atypical myxomatosis Abscesses Tumours Hernias Subcutaneous Cysticercus serialis cysts Enterotoxaemia Viral haemorrhagic disease Intestinal obstruction Choking Predator attack Trauma Acute pasteurellosis Electrocution Cardiomyopathy Neoplasia Poisoning e.g. yew Listeriosis Dental disease Gastrointestinal hypomotility Renal disease Caecal impaction Chronic liver disease Neoplasia Change of diet Bullying by cagemate Pseudotuberculosis Some fluffy haired breeds lose fur in patches Associated with pregnancy or pseudopregnancy Caused by dominant cage mate e.g. essential sulphur amino acid deficiency Rabbit syphilis e.g. fibromas Dogs/foxes are intermediate hosts Especially rabbits with advanced dental disease that can choke on pieces of hay Females in late pregnancy Hepatic coccidiosis in young rabbits prone to bacterial infection. Fat rabbits with excessive skin folds and large dewlaps experience problems grooming and may lick the cranial surface of the dewlap obsessively as a type of displacement activity because they cannot groom other areas such as the underside of the dewlap or the perineum which is infected, inflamed and sore. The forelegs are used to clean the face. Examination of the inner aspect of the carpus and metacarpus may show saliva staining indicative of dental disease. Dried mucopu- rulent material can be found in rabbits with ocular or nasal discharges. Examination of the fore and hind limbs may show evidence of ulcerative pododermatitis. An area of thin, hairless skin over the point of the hock is not unusual. It is protected by thick fur that is directed across it. Felts of densely matted hair are a cause of intestinal obstruction if the rabbit ingests them during grooming. Large felts can accumulate on the plantar aspect of the hind feet. Owners should be advised to groom these animals daily and ensure that loose felts of hair are removed. Rabbits with dental problems or long-haired breeds such as Angoras are especially at risk. 3.9.6 Examination of the perineum Examination of the perineum confirms the sex of the rabbit and gives an indication of general state of grooming. Urine scalding, vaginal discharges, adherent caecotrophs, fly strike, perineal fold dermatitis or diarrhoea may be evident on examination of this area (see Figure 3.2) The two deep folds of skin on either side of the anal orifice are the inguinal glands that are normally filled with a yellow-brown odiferous deposit (see Figure 3.1b). The perineum is an extremely sensitive area in rabbits. Pain caused by infected, inflamed perineal skin can lead to urine retention, urethritis, cystitis and/or urinary incontinence. Urine scalding can also be due to urogenital disease or indicative of other problems such as vertebral spondylitis, sore hocks or arthritis which prevent the rabbit positioning itself correctly to urinate (see Section 14.4.3). Neurological deficits, abdom- inal pain or generalized weakness can also lead to urine scalding or perineal soiling. Skin inflammation in the perineal area may be caused by uneaten caecotrophs that have become adherent to the fur and caused super- ficial pyoderma of the skin beneath. Obesity, dental disease and arthritis prevent grooming around the perineum so the fur becomes matted, soiled and infected. This starts a vicious circle that can be broken by clipping and cleaning the perineal area and treating the painful dermatitis (see Figure 9.1 and Section 9.7.3). Clippers can be used to remove most of the fur. A sharp pair of curved, pointed scissors is useful to tease out and cut matted hair around the genitalia and under the tail. Dead and matted hair can be combed out with a flea comb. It is very easy inadver- tently to damage the delicate skin. Patience and the correct equipment are required. Sedation may be needed. The underlying reason for urinary incontinence, cystitis, grooming difficulties or uneaten caecotrophs needs to be addressed to prevent recurrence. The appearance of the vulva alters accord- ing to the state of sexual receptivity. When the doe is non-receptive, the vulva is pale pink and dry. During receptivity, the vulva becomes swollen, moist and red, becoming darker until it is purple at the end of the receptive period. If the doe is mated, the vulva returns to a light pink colour in about 24 h. Inflamed or crusty skin around the genitalia can be associated with Treponema cuniculi or ectopic Psoroptes cuniculi infesta- tion. Ear mites can be transferred from the ears to the perineal folds during grooming. Examination of the external ear canal of affected rabbits reveals thick crusty exudate caused by P. cuniculi. Rectoanal papillomas can cause crusty lesions that protrude through the anal sphincter. The hydration status of the rabbit can be assessed during examination of the perineum. Dehydration can occur in the absence of obvious fluid loss due to the redistribution of water and electrolytes associated with alter- ations of gastrointestinal motility. Although rabbits do not to take on a ‘sunken eyed’ appearance when dehydrated, the thin skin becomes wrinkled and loses its turgidity. The hairless scrotal skin of males is a useful site to assess hydration status by tenting the skin. The inguinal skin can be used in females. 73The rabbit consultation Mucous membranes can be examined by looking at the colour of the nose or by lifting the lip to see the gums and tongue. Cyanosis is evident in advanced cases of cardiovascu- lar or respiratory disease. Mild anaemia is more difficult to elucidate although extreme pallor is obvious. 3.9.7 Rectal temperature The rectal mucosa is thin and easily damaged. Many practitioners do not routinely take the rectal temperature as part of their clinical examination because of the risk of trauma and the limitations in interpreting its significance. 74 Textbook of Rabbit Medicine
      
 
                       
  
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$ '&' $ +  Figure 3.2. Causes of perineal soiling in pet rabbits. A healthy, short-coated rabbit will meticulously groom its perineum and keep it clean. There are many inter-relating factors that can prevent effective grooming of this area and result in matted, soiled fur with or without inflamed underlying skin. Normal rectal temperature of rabbits is 38.5–40°C (103.3–104°F). It is affected by factors such as environmental temperature and restraint. There is a slight seasonal variation with temperatures being higher in the autumn and winter than in spring and summer. Females have a slightly higher rectal temperature than males (Pericin and Grieve, 1984). Temperatures below 38.0°C (100.4°F) can be considered subnormal and temperatures in excess of 40.6°C (105°F) are significant and indicative of pyrogenic infection (Toth and Krueger, 1989) or heat stroke. 75The rabbit consultation Ribs Xiphoid cartilage Liver Stomach Greater omentum Upper proximal colon Ampulla coli Jejunum Uterus Lateral uterine ligament Median ligament of the bladder Bladder Caecum Distal proximal colon Duodenum Figure 3.3. Topographic view of the abdomen, ventral view. The ventral abdominal wall has been resected to expose the viscera that are illustrated in situ. The diagram was drawn from post-mortem specimens using Barone et al. (1973) as a reference source. Key points 3.5 • Rabbits normally drink 50–100 ml/kg/ 24 h although the amount may vary with diet • Water deprivation results in anorexia • Food deprivation can increase thirst • Normal rabbit urine can be any colour from yellow, to brown orange or red • Normal rabbit urine is turbid • Immature rabbits can be sexed by evert- ing the genital orifice. The female has a slit like vulva. The male has a penis. Testicles descend at 10–12 weeks • Female rabbits have a dewlap • It is difficult to age live rabbits with any degree of accuracy • Examination of the perineum is an essential part of clinical examination. Urine scalding or faecal soiling may be indicative of other diseases • Normal rectal temperature is variable: < 38°C can be considered subnormal. > 40.6°C is significantly high. results in increased respiratory effort and may be accompanied by various snuffles, squeaks and whistles. Some short-nosed breeds always make this type of noise. The differentiation between upper and lower airway disease can be made by observation and auscultation and examination of the nose. An increase in respiratory rate is brought about by an increase in diaphragmatic rather than intercostal movement and can give the impression of dyspnoea. Dyspnoea is manifested by cyanosis, mouth breathing, depression and distress and may or may not be accompanied by an audible respiratory noise. Abnormal, absent or muffled lung sounds may or may not be heard during thoracic auscultation of rabbits with lower respiratory disease. Chronic lung disease cannot be ruled out by auscultation of the chest. Severe lung changes are a frequent incidental finding during post-mortem exami- nation. Abnormal heart sounds can sometimes be detected, although cardiac disease is rare in rabbits in comparison with lung disease. The list of differential diagnoses of dyspnoea is similar to other species. Normal heart rate varies between 130 and 325 bpm, which is too fast to differentiate heart sounds. Stress increases the heart rate markedly. A pulse can usually be felt in the central artery of the ear (Figure 3.6). A femoral pulse can sometimes be found although it is not as easy to locate in the rabbit as in the dog or cat. 78 Textbook of Rabbit Medicine Medial auricular a. Lacrimal a. Anastomotic ramus to internal carotid a. External ophthalmic a. Supraorbital a. Ethmoidal a. Buccal a. Infraorbital a. Major palatine a. Superior labial a. Inferior labial a. Lingual a. Mental a. Inferior alveolar a. Facial a. Linguofacial a. External carotid a. Transverse facial a. Occipital a. Superficial temporal a. Caudal auricular a. Medial auricular a. Caudal auricular a. Rostral ramus of Caudal auricular a. Intermediate ramus & Figure 3.6. Arteries of the head. The arteries of the cheek may be encountered during surgery on facial abscesses in rabbits. The buccal and lingual arteries are in close proximity with the cheek teeth and can be inadvertently punctured during tooth trimming. The arteries of the ear are also illustrated. A pulse can often be detected by placing a finger on the intermediate ramus of caudal auricular (central) artery of the ear. 3.9.10 Examination of the face, head and oral cavity The rabbit can be wrapped in a towel for this part of the examination and held firmly against the body of the owner or nurse. Visual inspection of the external ear canal may reveal the typical crusty exudate that is associated with Psoroptes cuniculi infestation or the waxy exudate that is often encoun- tered, especially in lop eared breeds. There is a blind ending section of the external ear canal separated by a cartilaginous plate or tragus. Examination of both sides of the tragus can be performed with an auriscope. Auriscopic visualization of the eardrum is difficult due to the length of the auditory canal and the presence of wax and debris. The skin around the face and head is normally clean and free from debris. Sometimes it is a bonded companion, and not the patient itself, that keeps the head groomed and cleaned. The presence of small scabs in the fur is indicative of a rabbit that is not grooming perhaps due to pain around the face. Saliva staining on the chin or around the mouth is usually indicative of dental disease, although moist dermatitis of deep skin folds under the chin occurs in some loose-skinned breeds. Epiphora causes tear staining and matted fur on the face beneath the medial canthus of the eye, which can lead to superficial pyoderma in that area. Occasionally this is associated with spurs on the upper premolars or molar teeth growing into the mucosa inside the cheek. Grooming the skin over the area becomes painful. The large ears of some lop eared rabbits can sometimes impinge on the eye and surround- ing structures causing trauma and irritation. The head should be palpated and carefully examined for the presence of abscesses on the side of the face, under the masseter muscles or along the bottom of the jaw. One side of the face can be compared with the other. Pain or bony swellings associated with elongated tooth roots can be detected by palpation of the ventral border of the mandible and the zygomatic area (see Section 7.7). The nares should be inspected for signs of a nasal discharge. The incisors are easily examined by retract- ing the lips. The molars and premolars can be visualized with the aid of an auriscope or vaginal speculum. With practice, normal and abnormal cheek teeth can be differentiated by this technique, although it is not always possible to determine the cause of an abnor- mality. Rabbits that resent oral inspection often have problems with their cheek teeth. Excessive saliva, halitosis, presence of food, blood or pus are indicative of dental problems and general anaesthesia is neces- sary to examine the mouth thoroughly. 3.9.11 Examination of the eyes Exophthalmos or glaucoma can be seen by comparing the size and shape of the eyes. Fear can cause the eyes to bulge out of the sockets due to engorgement of the orbital vascular sinus (see Figure 3.7) (Eglitis, 1964). Retrobulbar abscesses, tumours or cysts can cause a unilateral exophthalmos. The eyelids should be examined for evidence of wounds, ectropion, entropion, meibomian cysts or myxomatosis. The eyes should be clean and 79The rabbit consultation Key points 3.6 • Care should be taken during abdominal palpation as the thin walled viscera are easily traumatized • Both kidneys can be felt during routine abdominal palpation • The spleen is too small to be palpated • The stomach and liver are not usually palpable • The caecum may be palpated depend- ing on nature of contents and time of day • Palpating the bladder can elicit straining and urination in rabbits with cystitis • The uterus cannot be palpated in the non-gravid, healthy animal. During pregnancy it may be felt in the ventral abdomen • The thoracic cavity of the rabbit is small • Breathing takes place through the nose • Respiration is brought about by movement of the diaphragm rather than the intercostal muscles • Normal respiratory rate is 32–60 breaths per minute • Normal heart rate varies between 130 and 325 bpm • A pulse may be felt in the central artery of the ear. free from purulent discharge. The rectus dorsalis muscle can be seen attached to the dorsal sclera when the upper eyelid is retracted. Applying pressure to the area just below the medial canthus of the eye may squeeze pus out of the opening of the nasolacrimal duct in cases with purulent dacrocystitis. Nystagmus may be observed by watching the movement of the eye for a few seconds. Occasionally slow nystagmus can be seen in pet rabbits at rest in association with nodding of the head. Affected individuals are usually seropositive for Encephalitozoon cuniculi. Direct illumination of the eye may reveal pathological conditions of the cornea and uveal tract. Evidence of previous lens rupture and cataract formation is associated with Encephalitozoon cuniculi. Local anaesthesia with topical proxymetacaine drops facilitates examination of the cornea and third eyelid. The application of fluorescein will reveal corneal ulceration. The Schirmer tear test has been evaluated in rabbits. The test paper is inserted into the lower conjunctival fold in the lateral third of the eyelid and is held in place for 1 minute. The amount of wetness is measured in millimetres. Topical anaesthesia is not used. Normal values range from 0 to 11.22 mm/min with a mean of 5.30 + 2.96 80 Textbook of Rabbit Medicine Key points 3.7 • The tragus is a blind-ending section of the external ear canal separated by a cartilaginous plate • Wax and debris often obscure the ear drum especially in lop eared breeds • Bilateral exophthalmos can be caused by fear • Low Schirmer tear tests are of doubtful significance in rabbits • Rabbits produce atropinesterase that can interfere with topical atropine drops used to induce mydriasis. Superior labial v. Deep facial v. Lingual v. Inferior alveolar v. Inferior labial v. Linguofacial v. External jugular v. Retromandibular v. Pterygoid plexus Caudal auricular v. Medial auricular v. Intermediate auricular v. Medial auricular v. Caudal auricular v. Transverse facial v. Ophthalmic sinus Lateral nasal v. Figure 3.7. Veins of the head. The veins of the head include the marginal ear vein that is a convenient site for venepuncture. The large orbital venous sinus is also illustrated. This sinus may be encountered during enucleation of the eye and can be a source of serious haemorrhage.