Rabbits are now the third most popular pet in the UK. Unfortunately, many suffer from health problems that could be prevented with a little effort and understanding. While two important viral diseases — myxomatosis and rabbit haem-orrhagic disease — can be prevented by vaccination, many other common health problems in rabbits are the result of poor husbandry, and in particular incorrect feeding.
The most important parts of a rabbit to consider for its health are its teeth and its guts; if you can keep these healthy and working correctly, you are a long way towards maintaining a healthy rabbit.
Evolution
While selective breeding has changed external features, such as the domestic rabbit's coat colour, fur length, ear shape and size, its underlying physiology is, or should be, similar to that of the wild rabbit Oryctolagus cuniculus.
Rabbits evolved in the dry grasslands of Spain and Portugal. They have evolved to chew and digest large quantities of high-fibre, low-nutrient food, but they are also adapted to eat high-quality food when this is available; they are known as ‘concentrate selectors’, which means they choose the most nutrient-rich parts of the plants to eat (Meredith, 2011). Unfortunately, like humans, this means that if large quantities of high-quality food are available, they may eat too much of the wrong food.
Diet and teeth
Rabbits, like rodents, have teeth that grow throughout their lives. Unlike rodents, they have a second set of upper incisors, the peg teeth; the overall dental formula is I2/1 C0/1 P3/2 M3/3. These peg teeth are smaller than the first incisors and lie directly behind them. As with other mammals, the teeth are made up of enamel, dentine and cement. The main upper incisors have enamel on the front (labial) surface only, while the peg teeth and lower incisors have enamel on both the labial and buccal (inner) surfaces; the result is that natural biting of food produces an efficient, chisel-shaped cutting surface on these teeth. The cheek teeth (premolars and molars) have a complex folded structure. When rabbits chew, with their jaw moving from side to side as well as up and down, each upper tooth overlaps with the front part of one lower tooth and the back part of another; the ridges of enamel on the upper and lower teeth complement each other, providing a good grinding surface (Harcourt-Brown, 2002a; O’Malley, 2005).
In a healthy rabbit, the teeth are worn down by chewing on food at the same rate as they grow — about 3 mm a week (Meredith, 2011). Wild rabbits that eat a natural diet almost never have tooth problems; however, tooth problems are common in pet rabbits (Figure 1).
Some tooth problems are congenital in origin, such as in brachygnathic breeds where the upper and lower incisors may not meet properly. Most tooth problems, however, are acquired and develop gradually. Insuf-ficient calcium intake (for example when a ‘mix’-type diet is fed and the rabbit chooses not to eat the pellets containing most of the calcium), inadequate fibrous food or inappropriate forces on the teeth while eating unnatural foods have all been suggested as causes of acquired tooth problems. It is probable that causes vary and are multi-factorial, with two or more factors combining to result in problems. Once tooth problems start, the tooth surfaces no longer meet prop-erly, the teeth are no longer worn at the correct rate or in the correct pattern and the crowns and the roots elongate (Harcourt-Brown, 1997, 2002a).
There is a general consensus that the correct diet is the best way to prevent dental problems, such as plenty of grass or grass hay supplemented by a range of wild and cultivated green foods and only small amounts of concentrates (Box 1) (Bourne, 2009). Good-quality, sweet-smelling (not musty) grass hay should be used (Figure 2). Alfalfa hay is high in calcium; while this can be used for growing rabbits, in adults the excess calcium may contribute to ‘sludgy urine’ and urolithiasis (Richardson, 2000; Meredith, 2006). Pelleted concentrate foods have the advantage that each pellet is nutritionally balanced. If a mixed or muesli-type food is fed, it is important to provide only a small amount so that all parts are eaten. Rabbit food preferences tend to settle quite early, so ideally a rabbit should be introduced to a large number of different foods when still young, preferably during the weaning period, or the rabbit may refuse to eat many items (Meredith, 2011).
Box 1.Appropriate diet for the domestic rabbit
- A high-fibre diet is best to keep a rabbit's teeth and gastrointestinal system healthy
- Grass and/or hay should form the basis of the diet
- Straw is high in fibre but too low in nutrients
- A variety of green foods should be given daily, including wild plants and cultivated vegetables
- Sugar-rich vegetables and fruits should be given only in small quantities and as treats
- Only a small amount of concentrate food should be given; if this is a mix-type diet, the rabbit should eat all the parts of the mix
Diet and the gastrointestinal system
Non-digestible fibre is not only good for the teeth but is also essential for the proper functioning of the gastrointestinal system (Meredith, 2011).
The rabbit is a hindgut fermenter, like the horse. It has a simple, thin-walled, J-shaped stomach making up about 15% of gastrointestinal volume, and an unremarkable, relatively short small intestine; the large intestine is well developed. The caecum, which is the main fermenting chamber, makes up about 40% of total gastrointestinal volume; proportionate to body size, lagomorphs have a larger caecum than any other mammal and the complete gastrointestinal tract makes up 10–20% of their bodyweight.
More than half of the volume of the abdomen, mainly on the right side, is taken up by the ileocaeco-colic complex — the spiralling caecum accompanied by the ileum and part of the colon. The proximal colon has a complex structure, with three longitudinal bands and a large number of sacculations called haes-tra. Most of the time the muscular activity of the colon mechanically separates high- and low-fibre particles, with nutrient-rich particles being directed back to the caecum by the activity of the haestra in order to be metabolized, while high-fibre particles are quickly eliminated as small, dry pellets.
The caecum is where water, secreted into the proximal colon, is absorbed. It is also where digestible fibre is broken down by the complex microflora, and the volatile fatty acid products of the bacterial fermentation are absorbed for use by the rabbit (Harcourt-Brown, 2002a; Meredith and Crossley, 2002). If the balance of the caecal microflora is upset, pathogenic bacteria can proliferate and cause disease. A particularly critical time is around weaning, especially since many just-weaned rabbits are also subjected to the stress of being separated from their mother and siblings and moving to a new home (Meredith, 2006).
At certain times of the day, the activity of the colon changes and nutrient-rich material passes from the caecum to the fusus coli, a muscular and mucus-secreting area. Here the material from the caecum is formed into soft pellets and covered with mucus; these pellets are passed as caecotrophs. Normally the rabbit will swallow its caecotrophs whole as it produces them, as they are a source of important nutrients (Meredith and Crossley, 2002). Caecotrophs found inside the cage are a sign something is wrong; the rabbit may be overfed, thus not needing the additional nutrients from the caeco-trophs, or may be unable to bend to reach its anus because of physical difficulties such as obesity, spinal problems or pain. Rabbits with tooth problems, for example, may stop eating caecotrophs (and stop grooming) as a result of overgrown incisors making these activities difficult or due to the pain of tooth spurs digging into the soft tissue of the mouth. Overweight rabbits may have folds of skin around the tail that prevent them from reaching the anus properly — even a large dewlap may get in the way (Figure 3) (Richardson, 2000; Harcourt-Brown, 2002a).
A diet low in indigestible fibre reduces gastrointestinal motility; gastrointestinal motility is also reduced by stress, pain and fright. Low gastrointestinal mobility can lead to:
- The development of trichobezoars
- The accumulation of gas in the stomach and caecum
- Alterations in water and electrolyte secretion and absorption (with resultant imbalances)
- Changes in the pH of the caecum
- Alterations in the microbial balance in the caecum
- Possibly proliferation of pathogenic bacteria such as Clostridium spp.
Caecotrophs versus diarrhoea
Because caecotrophs are soft, they may be mistaken for diarrhoea when the owner finds them. If a rabbit has true diarrhoea, the owner will not be finding any of the normal, hard, dry faecal pellets around the cage, just the soft/liquid faeces. If normal, hard pellets are still being produced, the soft faeces will be caecotrophs and not true diarrhoea. Examined microscopically, the material inside caecotrophs is made up of small particles with bacteria, yeasts and protozoans (Rees Davies, 2006).
True diarrhoea
True diarrhoea may be of ‘cowpat’ consistency through to watery, with or without mucus and often smelling foul; it may contain blood. Diarrhoeic rabbits are usually depressed and anorexic. Examined under the microscope, the diarrhoea may contain an abnormal mixture of large particles (>0.5 mm) and small particles. True diarrhoea is more common in kits around the age of weaning than in adults. Causes include coccidiosis, salmonellosis (rare as a cause of diarrhoea), colibacillosis, Tyzzer's disease (Clostridium piliforme infection), rotavirus or coronavirus infections, and enterotoxaemias caused by Clostridium spiriforme or other organisms (Rees Davies, 2006).
Diet and obesity
Unfortunately, many pet rabbits are allowed to become obese. This is most likely to be related to excess food intake, although inadequate exercise also can play a part (Box 2). Rabbits fed mainly a high-fibre diet (grass hay) are much less likely to become obese than those eating mainly concentrates (particularly those provided with free access to palatable concentrate diets). Digestible fibre is a source of metabolizable energy to rabbits (via volatile fatty acids produced and absorbed in the caecum); therefore, a diet high in undigestible fibre is important to avoid obesity and is particularly appropriate for rabbits needing to lose weight (Harcourt-Brown, 2002a). Increasing the rabbit's exercise will also assist in weight loss, so the rabbit should be provided with opportunity and encouragement to exercise. Foods with a high fat content are more likely to lead to obesity and can cause changes in lipid metabolism, resulting in hepatic lipidosis.
Box 2.Causes and risks of obesity in domestic rabbits
- Rabbits fed large amounts or concentrates ad libitum are more likely to become obese
- Diets high in indigestible fibre are important to prevent and treat obesity
- Obesity increases the risk of several diseases
- Obese rabbits are more likely to develop anorexia in response to pain or stress
- Obese rabbits that stop eating for any reason are at particular risk of developing fatal hepatic lipidosis
- Obese breeding females are more likely to develop pregnancy toxaemia (usually fatal) in late pregnancy or when early lactating
- Dietary changes must be made gradually (e.g. over 2-3weeks) and with checks that the rabbit is eating the new diet and passing normal, hard faeces
- Encourage exercise alongside a healthy diet to prevent/treat obesity
Obese rabbits have a raised resting heart rate and may be at increased risk of developing hypertension, cardiac hypertrophy and arthritis. They may be less able to reach all parts of the body to groom themselves properly or to reach and eat their caecotrophs normally; thus they are more prone to parasitic skin diseases, perineal soiling and flystrike, and are more likely to develop sludgy urine, urine scalding and cystitis (Figure 3). Additionally, they are at increased risk of the development of hepatic lipidosis in the event of anorexia (see below) (Harcourt-Brown, 2002a; Rees Davies, 2006).
The importance of water
Rabbits normally drink 50–150 ml/kg bodyweight of water per day (Meredith and Crossley, 2002). Adequate water intake is essential for normal gastrointestinal gut function, and water must be freely available to the rabbit at all times and particularly on a dry diet (e.g. hay). Water is often provided in sipper bottles, because these are less easy for the rabbit to soil or knock over than traditional water bowls. However, Tschudin et al (2011) found that rabbits take longer to drink from a sipper bottle than from a bowl, requiring more laps of the tongue to take in the same amount of water. This may be a particular problem in sick rabbits, or if for example a rabbit has sharp tooth spurs digging into the tongue, making lapping painful (Harcourt-Brown, 2011).
Soiling and fystrike
Flystrike usually occurs in the summer, when flies are numerous and high temperatures enable the rapid development of larvae. Either uneaten cae-cotrophs or true diarrhoea may stick to the rabbit's fur and make it attractive to flies; skin and fur that is urine-soaked is also attractive, as are any wounds or weeping skin (Cousquer, 2006). Once flies lay their eggs, the hatching maggots quickly start to eat through soft, moist skin in soiled areas. Owners should clean their rabbit's hutch out frequently, particularly in summer, and should check under the rabbit's tail daily for any faecal matter sticking there. If the rabbit is soiled with faeces or urine, it should be cleaned by gentle bathing. However, it is important to consider what underlying problems might have caused the rabbit to get soiled. Additionally, the rabbit should be checked for any injury that might attract flies. Note that if flystrike is caught early, it can usually be treated successfully.
Hospitalization, feeding and anorexia
It is important to keep rabbits eating. A healthy rabbit always has food in its stomach and intestines. Rabbits cannot regurgitate and food should not be withheld before surgery, except perhaps for about 30 minutes before induction of anaesthesia, to reduce the chance of food in the mouth getting in the way during intubation. A hospitalized rabbit should be encouraged to eat by providing it with clean, sweet-smelling hay and tempting items, such as fresh-picked grass (not lawnmower clippings), dandelion leaves and fresh vegetables. A rabbit that is in pain may not eat; pain associated with tooth and mouth problems is particularly likely to discourage eating. A stressed rabbit is less likely to eat. Stress can be minimized and eating encouraged by:
- Housing the rabbit away from predators (e.g. cats, dogs, ferrets, birds of prey)
- Providing the rabbit with a cardboard box to hide in
- Providing the rabbit with familiar smells (e.g. hay, a blanket from home)
- Providing the rabbit with familiar food (if it is on a poor diet, this is not the time to change it)
- Providing a litter tray
- Ensuring pain is managed properly
- Giving it opportunity to exercise in a safe place
- Housing the rabbit (in the hospital) with its rabbit buddy, if possible.
Water should always be available, preferably in both a bowl (which rabbits generally prefer) and a sipper bottle (so that a source of water is available even if the bowl has been tipped over or soiled) (Harcourt-Brown, 2002b; Belle and Bourne, 2009).
The effects of anorexia show complex interactions (Harcourt-Brown, 2002c; Rees Davies, 2006):
- Lack of food intake can lead to hepatic lipidosis, which is often fatal, and ketosis, which leads to dehydration and electrolyte imbalances that in themselves can cause anorexia and may be fatal
- Reduced dietary fibre intake reduces substrate available for caecal fermentation (causing negative energy balance) and reduces gut motility
- Reduced gut mobility results in slower gastric emptying (which can itself cause anorexia), reduced substrates for caecal fermentation (thus less absorption of volatile fatty acids, causing negative energy balance), accumulation of gas in the gastrointestinal tract, which is painful (and pain can cause anorexia), promotion of gastric ulceration, which is also painful, and dehydration and electrolyte imbalances.
If a rabbit is anorexic (e.g. post-surgery), it is important to start hand feeding it quickly. Do not wait 24 hours to see if it starts eating; 48 hours of anorexia (less in young, pregnant, lactating or obese rabbits) can be life threatening. Syringe feed with as high a fibre diet as possible (i.e. the highest fibre diet that will still go though the syringe). In the UK, Oxbow Critical Care Diet (Oxbow) and Supreme Recovery Diet (Supreme Petfoods Ltd) are formulated for rabbits and other small herbivores. It is also possible to grind up pellets with water to give a slurry or to liquidize vegetables; additionally, it may be necessary to hydrate the rabbit. Make sure tempting foods are available at all times, as well as fresh water (Brown and Goodman, 2006).
Useful informationThe Rabbit Welfare Fund has published two leaflets on feeding domestic rabbits:
- Guide to Feeding your Pet Rabbit
- Going Green: Healthy Eating for Your Rabbit
Available from www.rabbitwelfarefund.co.uk
- To answer the CPD questions on this article visit www.theveterinarynurse.com
Approved by Harper Adams University College
Conclusion
Providing the correct diet helps to maintain both healthy teeth and normal gastrointestinal function in rabbits. Owners should be encouraged to feed their rabbits mainly grass or grass hay, with vegetables and only a small amount of concentrate food. Inappropriate diets may lead to dental disease, obesity and a range of potentially life-threatening gastrointestinal problems. Hospitalized rabbits should be encouraged to eat and drink by minimizing stress, treating pain and providing tempting food and water, thus preventing anorexia.
Key Points
- Rabbits have evolved to eat a high-fibre, low-nutrient diet; this is refected in the structure and function of their teeth and digestive system.
- An ideal rabbit diet is based on grass and/or grass hay; this promotes proper tooth wear and gut function.
- Rabbits produce two types of faeces, the final hard pellets and softer caeco-trophs; caecotrophs are normally re-ingested, whole, straight from the anus.
- Uneaten caecotrophs may be mistaken for diarrhoea; both may attract flies. A diarrhoeic rabbit is generally unwell and needs rapid treatment.
- Flystrike can be prevented by good hygiene and daily inspection; a rabbit with fystrike needs prompt treatment.
- Anorexia should be prevented if possible; start hand-feeding an anorectic rabbit early to avoid complications such as hepatic lipidosis.