Information for Vets
GASTROINTESTINAL PHYSIOLOGY AND DISEASE IN THE DOMESTIC PET RABBIT
by Susan A. Brown, DVM
An inappropriate diet may be the most common factor linked to disease in the domestic pet
rabbit. Dietary deficiencies in the rabbit can contribute to a wide range of conditions, including
dental, urogenital, cardiac and infectious diseases and behavioural disorders. The direct
effects of dietary deficiencies on the gastrointestinal tract (GIT) are an extremely common
cause of enteritis and obstructive GIT disease. Therefore it is important to understand basic
GIT physiology of this species, match this information to the lifestyle of the pet rabbit, and
formulate a healthy diet. There are many resources available that discuss the GIT physiology
of the domestic rabbit in great detail. An overview of this subject is presented below, and the
reader is encouraged to look further for more detailed information.
GASTROINTESTINAL PHYSIOLOGY
Rabbits are strict herbivores, and their relatively small body size makes it difficult for them to
store large volumes of coarse fibre. The indigestible fibre (in particular, lignocellulose) in the
diet is eliminated from the GIT quickly, which thus controls the rate of peristalsis. The digestible
portion of the diet is utilised to produce nutrients, some of which are absorbed directly through
the wall of the GIT and some of which are reingested, digested and absorbed in the form of
caecotropes. This particular system allows for a large volume of food intake with a rapid
digestive transit time, increasing the total amount of energy stored and minimising the need to
store fibre. The reingestion of nutrient-rich caecotropes is an important adaptation developed
by wild lagomorph ancestors to allow survival in the face of an unreliable food supply.1
Oral Cavity
The oral cavity, which marks the beginning of the GIT, contains open-rooted incisors and
molars. Proper wear of the teeth depends a great deal on the type of diet that is fed. Wild
rabbits take in a high proportion of tough, fibrous foods, which require a great deal of chewing.
Diets that require little chewing result in inadequate tooth wear. 2 An example of this is
commercial pellet diets, which are composed of tightly compressed small particles. Pellets can
be pulverised into a size that can be swallowed with a minimum of chewing. Feeding a diet that
is lacking in sufficient "chewing material" can lead to elongation of the crowns and/or the roots
of the teeth.2 Overgrown crowns can result in enamel spurs on the molars and malocclusion of
the incisors and/or molars. Hyperextended roots can lead to epiphora (from incisor roots
compressing the lacrimal duct) and abscesses (as the roots penetrate the mandible or
maxilla).2 Dental disease is a common cause of anorexia in the rabbit due to the pain
associated with these conditions. In rabbits with suspected dental disease it is important to
examine the mouth thoroughly and take high detail skull radiographs. Dental disease may be
one of the most underdiagnosed causes of anorexia in the pet rabbit.
Stomach
Ingesta next enter the simple stomach with its small, nondistensible lumen and muscular
pyloric sphincter. Rabbits are unable to vomit. The pH of the stomach is approximately 1 to 2 in
the healthy adult rabbit.3 The pH of the rabbit stomach preweaning is closer to neutral (5 to
6.5), and the gut is lacking in bacterial flora until about 4 to 6 weeks of age.4 After this time the
gut gradually becomes populated with living microorganisms and the pH of the stomach drops
to 1 to 2. The exact gastric pH in all states of disease is currently unknown but appears to
increase in the face of GIT disorders.5 A stomach food ball that contains sufficient fibre will
have an "open network" composition and can be easily penetrated by the gastric fluids, which
then sterilise the contents. A food ball that is composed of small particles that are compacted
tightly, such as with a diet high in alfalfa meal or commercial pellets, may not be well
penetrated and may allow passage of potential pathogens into the GIT.6 In addition, feeding
sufficient fibre promotes healthy peristalsis, aiding the rapid movement of material out of the
stomach and reducing the introduction of pathogens. A healthy rabbit’s stomach always
contains ingesta mixed with hair (due to normal grooming). It is not possible to remove the food
ball entirely by fasting. Instead, prolonged fasting may lead to the dehydration and impaction of
the food ball as well as hepatic lipidosis.7
Gastric Stasis ("Trichobezoars")
The condition commonly referred to as "gastric trichobezoars" or "hairballs" is a misnomer in
my opinion and that of others.7 The problem is primarily related to a chronic gastric
hypomotility resulting over time in an impacted, dehydrated food ball that cannot pass out of
the stomach. Since hair is always present in the rabbit stomach, when the food ball becomes
dehydrated, the hair becomes grossly more prominent, leading to the conclusion that the
original problem was hair. The onset of gastric stasis is usually gradual, with a decrease in
appetite and output of faeces; once complete stasis occurs, however, the rabbit becomes
anorectic. Anorectic patients may still be active and alert for several days before the condition
develops into a more severe and life-threatening GIT ileus. The most common cause of chronic
gastric hypomotility is low dietary fibre, but one or more other factors can be involved including
other dietary imbalances, inadequate water intake, inactivity, obesity, and concurrent disease.
The classic sign of gastric stasis is a full stomach with a halo of air around very dense ingesta.
In the past gastrotomy was performed in these cases, which often resulted in a high fatality
rate. The current recommended treatment for gastric stasis is aggressive medical therapy that
includes rehydrating the patient as well as the food ball, introducing high fibre force-feedings
(and ultimately correcting the diet long term), giving intestinal motility stimulants, and providing
other supportive care. The majority of mild to moderately affected cases respond to medical
therapy within 72 hours. Cases that do not respond in this time need to be reevaluated as
possible surgical candidates, but their prognosis is guarded to poor. Laxatives and proteindigesting enzymes such as pineapple juice have been recommended, but the use of these
products alone does not correct the underlying problem and I do not find them useful. There is
concern that long-haired rabbit breeds may accumulate an excessive amount of hair in the
stomach during seasonal moults. In my experience these breeds do not exhibit gastric
obstruction or stasis with any more frequency than any other breed if they are maintained yearround on a high fibre diet.
Caecum and Colon
Ingesta pass from the stomach into the small intestine, where they move rapidly toward the
ileocaecocolonic junction. At this point the ingesta enter the hindgut and move into the caecum
and the proximal colon. Through the contractions of muscular sacculations (haustra) in the
walls of the caecum and proximal colon, the indigestible fibre and digestible material are
efficiently sorted.3 Indigestible fibre migrates toward the centre of the intestinal lumen and is
moved distally, forming the hard faeces. Digestible material settles into the haustra and is
moved into the ceacum by reverse peristalsis of the proximal colon aided by fluid secretion into
the colon.3
The large, well-developed caecum is a blind sac containing anaerobic gram-negative bacteria,
including a predominant population of the bacilli Bacteroides.3 Many other organisms have
been isolated, including potentially pathogenic bacteria such as Clostridium spiroforme and
Escherichia coli, various protozoa, and a rabbit-specific yeast in the Saccharomycetaceae
family.8 These organisms are not pathogenic if their populations remain small; however, any
disruption of caecal environment (pH, motility, fluid content, dietary starch content, etc.) can
result in a floral imbalance, leading to enteric disorders. Lactobacillus spp. are not commonly
isolated in the rabbit caecum; therefore using oral Lactobacillus products in rabbits is of
questionable therapeutic value. In addition, Lactobacillus does not adhere to or colonise the
intestinal wall and is likely killed in the acid pH of the stomach or by the bile before it even
reaches the hindgut.7
Through fermentation of the digestible material, caecal flora produce amino acids, fatty acids,
and certain vitamins such as B and K.3 Some of these nutrients are absorbed directly
throughout the wall of the caecum, but most are returned to the rabbit via ingestion of its
caecotropes. The caecal contents are moved by periodic contractions through the large bowel,
resulting in the production of caecotropes. Caecotropes are soft, green, and mucus coated and
have a stronger odour than the hard faeces. They often appear in "grape-like" clusters. Rabbits
have a crepuscular life-style and tend to eat a larger volume of food at dawn and dusk.. They
produce hard faeces for approximately the first 4 hours after a large meal, with the caecotropes
produced during the next 4 hours.3 Rabbits ingest the nutrient-rich caecotropes directly from
the anus, so they are rarely seen in a healthy rabbit. The mucous coating protects the living
organisms in the caecotrope from the acid pH of the stomach for up to 6 hours. Most of the
caecal bacteria are ultimately killed and their contents absorbed, but a few may pass intact into
the intestine.6
It is interesting to note that dietary factors such as energy, fibre and protein will affect the
quantity of caecotropes consumed. An energy deficiency or high dietary fibre will result in the
total intake of caecotropes. Excess of dietary energy or protein may result in incomplete
caecophagy, with caecotropes being left on the cage floor. Since caecotropes contain vital
nutrients for the health of the rabbit, it is important to make sure that debilitated rabbits have
access to them. Rabbits that are obese or have perineal skin flaps or spinal, vestibular, CNS or
dental disease are at risk of developing nutritional deficiencies from the inability to ingest
caecotropes. Often these rabbits will find and eat their caecotropes if a solid floored cage is
used or if the owners place the fresh caecotropes where they can be reached by the pet.
Consider vitamin, amino acid and fatty acid supplementation of the diet if a rabbit patient is not
producing or ingesting normal caecotropes for a lengthy period.
GASTROINTESTINAL DISORDERS
Enteric disorders in rabbits can be caused by anything that disrupts normal GIT motility, the pH
of the caecum or the stomach, the fluid content of the ingesta (particularly in the hindgut), or
the hindgut flora. Some of these factors include low dietary fibre, high dietary starch or protein,
inadequate water intake, inactivity, stress, inappropriate antibiotic use, "bulk laxatives" (such as
psyllium, which retains fluid in the proximal colon), intestinal parasites, genetic predisposition,
and concurrent disease outside of the GIT.
Enterotoxaemia
The most severe form of enteritis, enterotoxaemia, is caused by a proliferation of Clostridium
spiroforme and the resultant iota-like toxin production. The disease is seen most often in newly
weaned rabbits (4 to 8 weeks of age) whose GIT has recently been populated with microbes. 7
Enterotoxaemia may also be created by administering inappropriate antibiotics to rabbits at any
age, although adult rabbits are more resistant. Antibiotics to avoid include clindamycin,
lincomycin, penicillin (orally, although in healthy rabbits on a good diet it may be used
parenterally), ampicillin, amoxicillin, amoxicillin-clavulanic acid, cephalosporins and
erythromycin.9 True enterotoxaemia results in severe depression, profuse watery diarrhoea
often tinged with blood, and death within 24 to 48 hours. It is extremely difficult to treat this
disease, and the best course of action is prevention through a healthy diet, low stress
environment and avoidance of inappropriate antibiotic use.
Chronic Soft Stools
By far, the most common form of enteritis seen in the adult pet rabbit is characterised by a
chronic soft stool produced intermittently throughout the day. The abnormal stools are mixed
with normal hard faeces and may range from "pudding-like" to soft clumps that adhere to the
rabbit’s perineum or environment. The soft stools have a strong odour and high mucus content,
which identify them as abnormally produced caecotropes. The rabbit may act relatively
normally otherwise, although some patients will exhibit periodic anorexia and abdominal
discomfort. Many of these patients are on a diet that is either low in fibre and/or high in starch
and are overweight and sedentary as well. The cause of this enteritis is likely a mild caecal
dysbiosis. Long-term progression of this disease may result in nutritional deficiencies (due to
the inability of the rabbit to ingest the liquid caecotropes) and, ultimately, to the more serious
condition of GIT ileus. Uncomplicated cases of intermittent soft stools in the rabbit are nearly
always treatable through correction of the diet. I have had success feeding these animals on a
100% ad libitum grass hay diet for 2 weeks (or until the stools have returned to normal, which
may take up to 2 months in some cases). Once the stools are normal, fresh leafy greens,
vegetables and fruits are reintroduced over the next 2 weeks. Commercial pelleted foods and
high starch foods (grains, legumes) are never returned to the diet. This diet not only results in a
rapid correction of the dysbiosis, but reduces excess weight naturally and safely. Rabbits
should also be encouraged to exercise, and fresh water should be available to them at all
times. A word of caution before embarking on this therapeutic plan: make sure that the rabbit is
familiar with hay and is eating it before removing all other foods from the diet.
Intestinal Ileus
Another common GIT disorder is intestinal ileus. This is often the result of a chronic GIT
hypomotility related to an inappropriate diet as was discussed with gastric stasis. The signs of
intestinal ileus are similar to those of gastric stasis (in fact, these disorders often occur
together) and include a gradual decrease in appetite and the size and number of hard stools
produced. The rabbit eventually becomes anorectic and sits hunched with abdominal pain.
Radiography reveals a gas-filled intestinal tract and caecum. Often there is a dense mass of
ingesta surrounded by a halo of air in the stomach, and occasionally the same sign is noted in
the caecum (caecal impaction). These cases are treated medically as described for gastric
stasis. Surgery should be avoided, and mild to moderate cases usually exhibit a return of GIT
motility and stool production within 72 hours.
Gastrointestinal Obstruction
Acute gastric or intestinal obstruction is seen more rarely than gastric stasis or intestinal ileus.
Obstructive disease is often confused clinically with ileus. The most common site of obstruction
is the pylorus or upper duodenum. The second most common site is the ileocaecocolonic
junction (the result being a caecal obstruction). GIT obstructions can also be caused by
postsurgical abdominal adhesions.
The material that most frequently causes an obstruction is a piece of dried ingesta mixed with
hair. This is not a true hairball as is seen in the cat or the ferret, but rather a matrix of food and
hair. Other foreign bodies include carpet fibres, plastic or rubber. I have encountered several
rabbits that developed complete GIT obstruction after ingesting large amounts of clay cat litter.
An accurate history reveals that the rabbit was perfectly normal one day and acutely depressed
and anorectic with no stool production the next; in contrast, ileus is characterised by a gradual
onset of signs. Radiographically, distention of the GIT with fluid and air is isolated to the
stomach and the duodenum with upper GIT obstruction. The stomach of an obstructed patient
appears grossly distended with fluid and some air, as opposed to the distinct halo of air seen
around the dense, distinct food ball of the gastric stasis patient. If the caecum is obstructed, it
will be greatly distended with fluid. GIT obstruction is an emergency situation requiring
immediate surgery. It can be very difficult to decompress the stomach via a stomach tube
because ingesta readily clog the tube. Administer glucocorticoids for shock, intravenous or
intraosseous fluid therapy, and analgesics and provide other supportive care as needed. The
prognosis is guarded to poor, even with aggressive therapy.
Bacterial Enteritis
Bacterial enteritis is rare in the adult rabbit, primarily because of the high stomach pH, which
sterilises the ingesta. It is more common in young rabbits, rabbits on a poor diet, or those
receiving inappropriate antibiotics for reasons already described. Bacterial enteritis can be
caused by infection with E. coli, Clostridium piliforme (formerly Bacillus piliformis; also known
as Tyzzer’s disease), Salmonella, Pseudomonas, and Campylobacter-like species.6 Viruses
are not a common cause of GIT disease in the pet rabbit in the United States. Rabbit enteric
coronavirus and rotavirus have been encountered in commercial rabbitries.6 Rabbit viral
haemorrhagic disease is found in China, Europe and Mexico but has not yet entered the United
States.
Parasitic Disorders
Parasitic disorders of the GIT of the rabbit involve coccidia (Eimeria spp.), Cryptosporidium,
Passalurus ambiguus, Passalurus nonanulatus, Obeliscoides cuniculi and a variety of cestodes
and trematodes.6 Coccidia are the most commonly encountered GIT parasites and may infect
either the liver (specifically Eimeria stiedae) or the intestine. Hepatic infections may be
subclinical or result in unthriftiness and death. Intestinal infection is often subclinical but
occasionally causes severe dehydration and death. Mild infections in healthy rabbits ultimately
result in long-term immunity. Treatment for coccidia involves the use of sulfa drugs. One
suggested treatment regimen for coccidia is sulfadimethoxine (15 mg/kg PO q12h for 10 days)
combined with a trimethoprim-sulfa combination (30 mg/kg PO q12h for 10 days).6
DIET RECOMMENDATIONS
The diet I recommend for the noncommercial, non-breeding pet rabbit is ad libitum grass hay
and large amounts of fresh leafy greens with added vegetables and fruits. Hay is the most
important part of the diet as it provides a naturally high indigestible fibre source and
encourages proper tooth wear. Good quality grass hay is also rich in other needed nutrients
such as protein, vitamins, minerals and carbohydrates. Grass hays available in the United
States include timothy, oat, barley and bromegrass or mixed grasses. Alfalfa hay can be used
if grass hay is not available, but it is higher in protein, calories and calcium, which may be
undesirable in some patients. I have found it more difficult to return overweight animals to their
proper weight and to control some cases of chronic soft stools if patients are fed large amounts
of alfalfa hay. In addition, it is not helpful to mix grass and alfalfa hay, as the more palatable
alfalfa hay will be eaten exclusively and the grass hay left behind. I have placed pet rabbits on
an all hay diet for up to 4 months to treat GIT disorders without ill effect.
The three main drawbacks to hay are:
 Some humans are allergic to hay dust and cannot be exposed to it. ·
 [US only] Hay can contain the eggs of Baylisascaris procyonis (the raccoon
roundworm) if it was taken from the top of the pile in an open hay loft or left outside on
the ground uncovered.
 It may be difficult to obtain quality grass hay year-round, making client compliance
difficult.
A less desirable but usable alternative to loose hay is pressed hay cubes which can be
purchased in some pet and feed stores.
The second most important part of the diet of the pet rabbit is clean, fresh leafy greens,
including kale, collards, beet tops, carrot tops, parsley, dandelion greens, chicory, mustard
greens, romaine lettuce, raspberry leaves, basil, mint, endive, radicchio, wheat grass and
Swiss chard to name a few. A minimum of three different greens should be fed daily, but the
more variety the better. If the rabbit has never had greens, establish it on hay first; then
introduce a variety of greens over a few weeks at a minimum amount of 1 cup of tightly packed
greens per 1kg body weight per day. Once rabbits are well established on this diet, the total
volume of greens is unrestricted. Rarely, an owner will observe a soft stool in relation to a
particular green food (parsley is a common culprit); that food may be removed from the diet.
Rabbits that ingest large amounts of greens will greatly decrease the amount of water they
drink. Other fresh foods fed in smaller amounts include carrots, pea pods, green pepper,
broccoli, Brussels sprouts, melons, berries, apples, pears, peaches, papaya, pineapple and
mango. Avoid feeding legumes or grains (including bread, cookies, oats and corn), which are
high in starch, and grapes and bananas, which often are "addictive". Fresh food provides not
only important fibre, fluid and other nutrients but also likely provides stimulation in terms of
different tastes and textures of foods. I have found that rabbits fed a diet comprised primarily of
grass hay and fresh foods are less likely to chew their own or other rabbits’ fur and are less
likely to spend time chewing on cage bars, dry wall, furniture and newspaper.
Owners like to feed "treat" foods, and they can be encouraged to find special fresh foods,
particularly fruits, that can be used in this manner. In addition, fresh non-toxic tree branches,
blocks of untreated soft wood and unfinished grass or wicker baskets can all serve as excellent
"dietary toys" as well as exercise for the teeth. The least important part of the diet of the
noncommercial, nonreproductive pet rabbit is commercial pellets. In my experience the ad
libitum feeding of a variety of commercial pellets has contributed to innumerable cases of
dental disease, obesity, enteritis, ileus and gastric stasis. Since removing or severely restricting
commercial pellets in the diet of the pet rabbit and supplementing it with hay and greens, the
frequency with which these conditions are seen has been reduced dramatically. Commercial
pellets are based on alfalfa meal, grains and other supplements and are designed for the rapid
growth of the commercial or laboratory rabbit that is usually not intended to live out its full life
span. To the credit of some feed companies there are commercial pellets now being produced
that are more suitable for the pet rabbit. They have a high fibre content (18% minimum), a
moderate to low protein level (14%-16%) and low calcium and fat. These "pet rabbit" pellets
can be used in situations where a weight gain is desired, where fresh hay cannot be fed, or
where client compliance feeding the "natural" diet is poor. Unless a weight gain is desired, the
amount of any pellets used in the pet rabbit diet should be restricted.
Fresh water is offered free choice and should not be contaminated with supplements, which
may reduce water consumption. As mentioned, rabbits on a diet high in fresh foods drink
considerably less water than a rabbit on a pelleted or all hay diet. Rabbits should be
encouraged to exercise daily; ideally, they should not be kept in cages bur rather in large pens.
Daily exercise has multiple health benefits including improvement of GIT motility.
The solution to many rabbit health problems is feeding an appropriate diet for this species. The
biggest obstacle to a healthy diet is client resistance to abandoning what has historically been
touted as the "proper" rabbit diet (i.e. pellets). In addition, clients like to feed their rabbits an
assortment of treat foods that are usually high in fat or starch, which only complicates matters
further. It is important to remember that often they neglect to mention these treat foods when
you are trying to resolve a problem case (e.g. chronic soft stools). However, with aggressive
education efforts and demonstration of the immense benefits of a proper diet, clients can be
won over. Once a lethargic, overweight rabbit that produced soft stools has been on a healthy
diet for a few weeks, I often hear comments like "I didn’t know he had that much energy! He
isn’t a ‘couch rabbit’ any more".
References
1 Krull WH: Coprophagy in the Wild Rabbit (Sylvilagus nutalli granger) (Allen). Vet Med 35:481483, 1954.
2 Crossley DA: Dentistry for Small Animals other than Cats and Dogs. Second Annual Midwest
Exotic Pet Seminars Proceedings, Schaumburg, IL, March 1997.
3 Cheeke PR: Rabbit Feeding and Nutrition. Orlando, Academic Press, 1987, pp 20-21.
4 Smith HW: The Development of Flora of the Alimentary Tract in Young Animals. J Pathol
Bacteriol 89:95-122, 1965.
5 Brooks DL: Rabbit Gastrointestinal Disorders, in Kirk RW (ed): Current Veterinary Therapy
VIII. Philadelphia, WB Saunders, 1983, pp 654-657.
6 Brooks DL: Nutrition and Gastrointestinal Tract Physiology, in Hillyer EV, Quesenberry KE
(eds): Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. Philadelphia, WB
Saunders, 1977, p 148.
7 Harkness JE, Wagner JE: The Biology and Medicine of Rabbits and Rodents, ed 4. Media,
PA, Williams & Wilkins, 1995
8 Forsyth SJ, Parker DS: Nitrogen Metabolism by the Microbial Flora of the Rabbit Caecum. J
Appl Bacteriol 58:363-369, 1985.
9 Jenkins JR: Gastrointestinal Disorders, in Hillyer EV, Quesenberry KE (eds): Ferrets,
Rabbits, and Rodents: Clinical Medicine and Surgery. Philadelphia, WB Saunders, 1977, pp
176-188.
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