Gastrointestinal disease in rabbits is common, and practical experience and observation demonstrate that in the clinical setting,
is commonly related to inappropriate diet.
Gastrointestinal Anatomy and Physiology
The Gastrointestinal Tract
The gastrointestinal tract of the rabbit is designed for digestion of large quantities of high-fiber food. A number of features
distinguish the digestive tract of the rabbit from domestic carnivores; the stomach comprises about 15% of the gastrointestinal
tract volume, and vomiting is prevented by the presence of a well-developed sphincter. The largest potential volume of the
digestive tract is made up by the cecum, which empties and fills depending on food intake and time of day. Nutrients are absorbed
in the small intestine similarly as in other species. It is in the digestion of fiber that the rabbit differs most dramatically.
The ileocecocolic section (junction of the ileum, cecum and colon) allows separation of food into large, indigestible particles
of fiber, which are sent into the colon for water absorption and elimination, and smaller particles and fluid, which are directed
into the cecum for bacterial fermentation. Once fermentation is complete, the cecum sends material into the large intestine.
These "soft feces" or cecotrophs are excreted 1-2 times daily, and swallowed whole in the healthy, normal rabbit.
The microflora of the intestinal tract of the rabbit is tightly regulated. Intestinal motility is stimulated by the presence
of indigestible fiber.
Components of an Appropriate Diet
The rabbit is a strict herbivore, and the digestive tract is adapted for diets high in fiber. The natural diet of the rabbit
is a variety of grasses that vary as to season and location. The dietary requirements of laboratory and production rabbits
are well known, but there is debate as to the ideal diet for the non-producing long-term pet rabbit. Complete pelleted rations
are available, but there is evidence many may be inadequate, inappropriate or designed for consumer visual appeal, i.e. those
containing grains and dried fruits. Recommendations for use of commercial pellets should be given with care after careful
evaluation of each ration. The ideal pellet is made primarily of grass hay with an appropriate vitamin and mineral mix, has
larger particle size, and does not allow the rabbit to pick out preferred portions. Most experts recommend limiting the amount
of pellets fed on a daily basis.
Hay is an important component of the diet of captive rabbits, but can vary dramatically in nutritional quality. High quality
grass hay is readily available in the United States, and should be available at all times.
Ideally, rabbits should be allowed outdoors for exercise and to graze on natural untreated grasses. In addition, most recommend
rabbits be offered a wide variety of green foods and vegetables, but debate exists on the percentage green foods should make
in daily food intake.
Pathophysiology and Symptoms of Gastrointestinal Disease
Any disruption of the normal digestive process in rabbits can result in gastrointestinal disease. For example, anorexia secondary
to dental disease reduces the amount of fiber for the digestive tract, resulting in gastrointestinal hypomotility. Hypomotility
can result in alterations in cecal microflora with proliferation of pathogens, or overgrowth of naturally occurring Clostridia spp. Worst-case situations can result in enterotoxemia and even death. Hypomotility is also produced by psychologic stress (fear,
change in environment, transport, pain) and stress secondary to other disease processes. Inappropriate diet as a cause of
hypomotility is discussed below.
Signs and symptoms can include anorexia, food and gas distention of the stomach and digestive tract (bloat), discomfort, the
presence of uneaten cecotrophs (often referred to as "diarrhea" by owners) and true diarrhea.
Dietary Cause of Gastrointestinal Disease
Most diseases of the gastrointestinal tract are related to diet and disruption of the finely balanced digestive process. Dietary
causes include abrupt change in diet, inappropriate food items (grains, large amounts of fruit) and diets generally low in
fiber.
Abrupt diet change is commonly implicated in gastrointestinal disease in many mammalian species; therefore, changes in diet
should be made gradually. A common scenario is anorexia and diarrhea after consumption of a large amount of unfamiliar green
food items. This common occurrence is often the root of the fallacious belief that greens are not good for rabbits, a belief
that is still commonly propagated among rabbit breeders and clubs.
