Gastrointestinal tract stasis is a slowdown of the normal digestive processes in rabbits or other small herbivores (guinea pigs, chinchillas). It shares some traits with colic in horses, or functional ileus in dogs and cats. GI stasis can occur in any rabbit of any age or reproductive status, usually secondary to any physiological stressor, including dietary imbalances; painful conditions such as dental overgrowth, pododermatitis, or arthritis; severe and prolonged emotional stress; infectious disease including upper respiratory or E. cuniculi; heavy metal toxicity; or renal or liver disease, including liver lobe torsion.
Once a gastrointestinal slowdown first begins, water is absorbed from the stomach. This begins to dehydrate the ingesta, leading to a dry ball of plant matter that cannot pass readily through the narrow isthmus to the cecum. This leads to additional ileus, and can result in a dysbiosis of normal flora in the cecum. If anaerobes in the cecum overgrow, they can release toxins that can produce diarrhea, enterotoxic shock, and death.
On physical examination, the rabbit is usually subdued but responsive. Mucous membranes should be of normal color and heart rate and respirations may be normal to slightly elevated. Temperature should be normal; hypothermia is a hallmark of shock. The abdomen may be difficult to palpate due to discomfort, but a firm or doughy stomach with a gassy or liquidy cecum are typical.
Radiographs can be helpful in confirming the presence of gastrointestinal stasis — typically the stomach has dense radio-opaque ingesta, may be slightly distended, and may show a gas cap on top of the ingesta. The cecum may be full of ingesta, liquid, or gas, or may be completely gas-distended in severe cases.
Principles of treatment include rehydrating the stomach contents by parenteral fluid administration, as well as syringe-feeding a liquid diet (Critical Care Herbivore from Oxbow Pet Products). Prokinetic agents such as cisapride or metoclopramide are routinely used once gastrointestinal obstruction has been ruled out. Adequate analgesia is imperative, since rabbits are prey animals whose physiology has not evolved to withstand significant pain. Many practitioners have used NSAIDs successfully, but this is becoming more controversial in cases of ileus when other modes of analgesia are available. I prefer to use buprenorphine to ensure adequate analgesia, and will often send the rabbit home on Tramadol if discomfort is still present. Antibiotics for anaerobes may be indicated especially if significant gas is present, and over-the-counter simethicone may be given to increase comfort.
Identifying the underlying cause is vital to successful treatment, as some etiologies can be life-threatening, and most if not corrected will cause the gastrointestinal tract stasis to recur. Diet should be high in fiber and low in sugar and other simple carbohydrates, and molar overgrowth if present should be identified and corrected. If the gastrointestinal stasis recurs despite an excellent diet and normal dentition, additional medical workup is warranted.