Managing gastrointestinal disease in rabbits (Proceedings)

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.

Trichobezoars are accumulation of large amounts of hair in the stomach. Ingestion of hair is a normal part of the grooming process, and ingested hair normally passes through the digestive tract. The presence of abnormal accumulations of hair are linked to low-fiber diets, other diseases disrupting the digestive tract, or excessive ingestion of hair during molt (especially in long-haired breeds) or due the presence of diseases of the skin.

Non-dietary Causes of Gastrointestinal Disease

As mentioned above, any disease processes leading to decreased appetite and anorexia can produce hypomotility and gastrointestinal disease. While the overwhelming majority of gastrointestinal disease processes in rabbits are directly or at least secondarily related to inappropriate diet, other primary etiologies have been documented.

Primary gastrointestinal disease due to the presence of enteric pathogens is uncommon in rabbits, but can include organisms such as E. Coli and Rotavirus. Clostridial species are normal inhabitants of the rabbit gastrointestinal tract, and can proliferate under certain conditions, producing severe enteritis and in some cases enterotoxemia. Clostridial overgrowth is linked to low fiber, carbohydrate diets, and administration of certain antibiotics, in particular oral penicillins, clindamycin, lincomycin or erythromycin.

Gastrointestinal parasites uncommonly produce disease, but coccidia can be a significant pathogen in young rabbits and those housed in over-crowded, stressful conditions.

Foreign body obstruction has been documented in rabbits, but is uncommon. Foreign material implicated includes paper, fabric, and dried peas or beans. Other documented causes of obstruction include neoplasms, tapeworm cysts, abscesses and adhesions.

Cecal impaction is another unique disease presentation, and is characterized by the presence of hard, firm material (usually food) in the cecum. It is frequently accompanied by stress and dehydration, but other underlying causes are uncertain.

A rare congenital condition of rabbits is dysfunction of the autonomic nervous system of the gastrointestinal tract, or dysautonomia, and results in variable symptoms of gastrointestinal disease. Diagnosis is via histopathology of affected nerves.

Other uncommonly reported diseases of the gastrointestinal tract include toxin exposure (plants, heavy metals) and coronavirus, which has been reported in a research colony.

Complications of Gastrointestinal Disease

Hepatic lipidosis is a common consequence of anorexia. Fat accumulation in the liver can result in eventual liver failure and death.

Diagnosis of Gastrointestinal Disease

Physical examination findings depend on the extent of disease and the presence of other underlying disease processes. Rabbits can present bright and alert with minimal significant findings, to moribund. A common presentation in the anorexic rabbit with gastrointestinal stasis is depression, a hunched, painful posture, palpable gastrointestinal gas with associated pain upon palpation.

Basic diagnostic testing can be useful, especially in rabbits with other underlying disease processes such as renal disease. However many rabbits with primary gastrointestinal disease do not present with significant alterations in complete blood count and chemistry analysis. Anorexic rabbits may demonstrate elevations in hepatic enzymes due to hepatic lipidosis. More debilitated animals show alterations in BUN and albumin consistent with dehydration.

In the author's opinion, the most useful test for direct evaluation of the gastrointestinal tract is high quality radiographs of the abdomen in two views. Contrast studies are described infrequently in rabbits, but may be useful in some cases.

Primary bacterial gastroenteritis is uncommon in the rabbit; therefore fecal culture and sensitivity are less useful in this species. The most appropriate application of this test may be rabbits with true diarrhea without history of inappropriate diet, or history of exposure to potential bacterial pathogens.

Fecal floatation is useful in rabbits with diarrhea, especially in younger rabbits where primary coccidia is more common.

Treatment of Gastrointestinal Disease

It must be emphasized that the overwhelming majority of rabbits with gastrointestinal disease as a consequence of inappropriate diet, or secondary to psychologic stress, or stress of other underlying disease processes respond well to administration of fluids, analgesics, motility enhancing drugs and hand (force) feeding. Rabbits with diarrhea should never be fasted, as is often recommended for carnivorous.

The following clinical findings indicate a critical patient that must be managed with extreme caution: marked depression and/or failure to respond to stimuli; marked to severe accumulation of gastric and/or intestinal gas, and indications of shock, including hypotension.

Treatment consists of the following elements (Table 1):

Table 1. Therapeutic agents commonly used in the treatment of gastrointestinal disease in rabbits.

1. Hospitalization. This is beneficial to observe condition, fecal output and response to therapy

2. Fluid therapy. The aim of fluid therapy is to correct hypovolemia and hydration deficits, and to help rehydrate the gastrointestinal tract to facilitate passage of contents. In mild cases, fluids can be administered orally or subcutaneously. However, moderate to severe cases greatly benefit from aggressive intravenous fluid therapy. Fluid choice and rate is determined by patient condition.

3. Pain and anxiety management. Both contribute to stress and will exacerbate impaired motility and contribute to treatment failure.

4. Support feeding. Hand feeding is a critical component to therapy. The ideal product for support feeding is a balanced liquid formula able to pass through a syringe or nasogastric tube. Rabbits with suspected gastrointestinal obstruction, or gastric stasis with a full stomach should be fed with caution.

5. Motility modifying drugs. These drugs are extremely beneficial for hypomotility disorders, but should be avoided in cases of suspected gastrointestinal obstruction.

6. Antibiotics. Antibiotics are indicated for suspected cases of enterotoxemia and primary bacterial enteritis only. These drugs are of limited benefit for gastrointestinal disease secondary to other disease processes.

7. Anti-ulcer therapy. There is some evidence prolonged anorexia contributes to gastric ulceration.

True gastrointestinal obstruction requires surgical intervention. Prognosis is dependant upon overall patient condition and higher success rates are linked to early intervention.

Rabbits that are unable or refuse to take hand-feeding formula benefit from placement of a nasogastric tube. Placement of a tube is easier in larger rabbits. Tube size ranges from 5 to 7 Fr. Tube length is determined by measuring from the tip of the nose to the last rib. Lidocaine gel is placed in the nostril and the rabbit carefully restrained with the head ventrally flexed. The tube is placed ventrally and medially into the ventral meatus, and advanced until it enters the stomach. Correct placement can be confirmed several ways, including by aspiration of stomach contents, and radiographically. The small diameter of the nasogastric tube imposes severe limits on products that will readily pass through it. Options include strained vegetable baby food, and finely ground critical care formula (Critical Care Fine Grind, Oxbow Hay Company, www.oxbowhay.com).

References:

Harcourt-Brown F. Digestive disorders. In: Textbook of Rabbit Medicine. Butterworth-Heineman, 2002.

Jenkins J. Gastrointestinal diseases. In: Ferrets, Rabbits and Rodetns Clinical Medicine and Surgery, Quesenberry KE, Carpenter JW (eds). St Louis, MO, Saunders, p 161-171.