Diagnosing and treating gastric ileus/stasis in rabbits (Proceedings) - Veterinary Healthcare
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Diagnosing and treating gastric ileus/stasis in rabbits (Proceedings)


CVC IN BALTIMORE PROCEEDINGS


Because practitioners are increasingly being asked to provide health care for rabbits, they need to know that the most common clinical problems seen in this species involve the gastrointestinal tract. Practitioners also need to know that rabbits have evolved as a prey species, and their survival reaction is to be very still in an effort to avoid detection. If this strategy is unsuccessful, rabbits can have rapid bursts of speed to avoid capture. These behaviors also "carry-over" in most domestic rabbits, and may result in an animal appearing stoic when stressed. Stressed animals are more susceptible to health problems, which initially result in anorexia and changes in the frequency and consistency of their pellets.

Anatomy

The abdominal cavity of rabbits is large, with the gastrointestinal tract being relatively long, and its contents can make up 10-20% of the body weight. The stomach typically contains 15% of the alimentary tract ingesta and serves as a reservoir for much of the ingested feed. The cardia and pylorus are well developed. Rabbits are unable to vomit because of the enteric arrangement of their cardia and stomach, and their pylorus is easily compressed by the duodenum, which exits at an acute angle. Gastric distention or compression due to a fur-ball, gas, or hepatomegaly contributes to pyloric compression and prevents emptying.

The small intestine is shorter in rabbits than in other species, and makes up about 12% of the gastrointestinal tract volume. The terminal portion of the ileum ends in the cecum and is expanded as the rounded sacculus rotundus (a common site of foreign body impaction). The rabbit's large, thin-walled, coiled cecum holds about 40% of the ingesta. This structure ends in a thick-walled, vermiform appendix that is characterized, like the sacculus rotundus, by lymphatic tissue. The cecum is the largest and most prominent organ of the abdominal cavity. Sacculations and bands characterize the colon, which starts from an area of the cecum known as the ampulla coli.

Digestive physiology

Following is a brief outline of some of the characteristics of rabbit digestive physiology:1-3
     1. Rabbits are herbivorous and their gastrointestinal system combines a simple stomach with hindgut cecal fermentation to efficiently ingest large quantities of poorly digestible fiber that is essential for normal peristalsis.
     2. Dietary fiber primarily stimulates gut motility rather than serves as a source of nutrition.
     3. Rabbit teeth are developed for a high-fiber, herbivorous diet. Chewing is characterized by up to 120 jaw movements per minute with a lateral motion, which helps keep the constantly growing teeth worn down.
     4. Normal peristaltic movements propel the larger, less dense fiber particles through the colon, while reverse peristalsis of the haustra of the colon move the fluid and small particles (the higher density components) retrograde to the cecum. Small particles and fluid are retained in the cecum, allowing for extensive fermentation.
     5. Cecal contents are expelled at intervals and consumed directly from the anus (cecotrophy). The cecotrophes have an outer greenish membrane of mucus that encloses semiliquid cecal ingesta; they contain high levels of vitamins B and K and twice the protein and half the fiber of hard feces.
     6. The most common cecal bacteria are anaerobic, gram-negative bacilli in the genus Bacterioides and large anaerobic metachromatic staining bacteria. Large ciliated protozoa are also present.
     7. Consumed microorganisms do not normally reach and infective dose in the small intestine because they succumb to the stomach's low pH of 1-2. When a rabbit's gastrointestinal system is compromised, common rabbit enteropathogens can "overgrow", and become invasive and produce toxins.

Nutrition

Rabbits require large amounts of fiber in the diet (15-16% crude fiber) to promote intestinal motility and minimize intestinal disease. Diets low in fiber promote an increased incidence of intestinal problems such as hypomotility and prolonged cecal retention time, causing reduced feed intake and predisposition to diarrhea. Coarse, nondigestible particles stimulate normal gastrointestinal processes including secretion, digestion, absorption, peristalsis, and excretion. Normal peristalsis occurs with the ingestion of a high-fiber diet, which provides a large particle size and which results in a lattice-like food ball for effective gastric acid penetration. Incomplete penetration of foods with small particles by gastric acid may result in the production of hard-packed food balls, especially in rabbits with marginal water consumption.

The preferred diet for the pet rabbit is a high quality, high fiber (15-16% crude fiber) pelleted diet containing 13-18% (ideally 16%) crude protein, at the rate of cup pellets per 2.3 kg body weight divided into two meals per day. A fiber content below 15% may increase the potential for anorexia and diarrhea, and one over 16% reduces feed palatability. However, a fiber content of 18-22% appears to help prevent obesity in pet rabbits and is useful for long-term use in mature laboratory animals. Because it is generally lower in protein and calcium and higher in fiber, grass hay (timothy, prairie, oat, etc.) is recommended over legume hay (i.e., alfalfa) for mature pet rabbits. Pelleted diets formulated from timothy hay (i.e., Bunny Basics/T, Oxbow Pet Products, Murdock, NE) are commercially available for adult pet rabbits. These diets are intended to help prevent obesity, urolithiasis or urinary "sludge," and gastric stasis.

Some rabbits do well, though, when pellets are offered ad libitum, unless overeating and obesity become problems or unless an adequate amount of loose hays are not consumed. The pellets are supplemented with loose hay (mixed grass hay, timothy hay, or high quality dried grass clippings) and provided ad libitum. Alfalfa hay can be offered throughout the growth stages, then discontinued because of its high protein and calcium content. The diet can be supplemented with a small amount (up to one cup) of dark fibrous, leafy greens (kale, mustard greens, carrot tops, parsley, or dandelion greens) and fresh vegetables (carrots, broccoli, green peppers, cauliflower, or cabbage) per 2.3 kg body weight daily or several times per week. In addition, rabbits can receive a small amount (up to one tablespoon per 2.3 kg body weight) of fresh fruit (strawberries, other berries, apples) daily or several times per week. It should be noted that growing rabbits and females in late gestation may require twice as much food as an adult rabbit at maintenance; lactating does may consume three times as much food as an adult in maintenance.


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Source: CVC IN BALTIMORE PROCEEDINGS,
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