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Gastrointestinal disease in ferrets and rabbits (Proceedings)

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Aug 01, 2011

Rabbit

Anatomy

Sacculus rotundus; spherical thick-walled enlargement at ileocecal junction. The adjacent cecum has a round patch of lymphoid tissue called the cecal tonsil. The increased thickness of these two lymphoid structures is due to aggregates of organized lymphoid tissue and macrophages in lamina propria and submucosa. Important to recognize this palpable thickening as normal.

     • -80% of food eaten should reach the cecum within 12 hours of ingestion.
     • -In the colon ingested contents are separated according to size and density: fluid and nutrient-rich particles of greater density settle into haustra (sacculations), and the less dense fiber particles accumulate in the colon's lumen. Taenia (bands) move the fiber antegrade to be eliminated as hard feces, while reverse peristalsis of the haustra move fluid and nutrient rich particles retrograde into the cecum where bacterial fermentation forms B-complex vitamins, protein, and fatty acids. Some of these nutrients are absorbed directly across cecum wall but most are formed into cecotrophs which are usually passed within 4 hours of hard feces. Large, undigestible fiber particles (lignin) are necessary for normal motility of rabbit's cecum and colon.

Gastrointestinal stasis

Gastrointestinal (GI) stasis is a syndrome where the normal muscular contractions of the stomach and intestines are greatly diminished and with time the normal intestinal/cecal bacterial flora is thrown off balance. Several factors can be involved including environmental stressors, pain from other underlying conditions such as dental/tooth points or spurs, and most commonly inappropriate diet. Feeding simple carbohydrates such as breadstuffs or cereals along with a lack of crude fiber can predispose to GI stasis. In the absence of adequate fiber the gastrointestinal tract slows down, which may result in subsequent changes in the cecum pH fermentation and bacterial populations and subsequent worsening of GI stasis. The rabbit with GI stasis will be anorexic or have a reduced appetite. An affected rabbit produces very small stools or none at all and may be hunched-up or grind its teeth in response to painful gastrointestinal gas formation. Diarrhea with mucous may or may not be present. Abdominal auscultation may reveal normal or hyperactive gut sounds early in the course of the disease with decreased to no gut sounds with disease progression. The sooner the problem is recognized the better the chance for full recovery and survival. Rabbits presented in obvious distress and with a palpably enlarged, non-compressible stomach warrant close monitoring and critical care. Rabbits with intestinal obstruction are occasionally presented and create a diagnostic and therapeutic dilemma. Most commonly due to a small trichobezoar or hair filled cecotroph, the duodenum is a common site of obstruction, followed by pylorus or ileocecocolic junction. Radiographically, the stomach is filled with gas and/or fluid and food and loops of dilated intestine proximal to site of obstruction may be seen. If the obstruction passes through the ileocecocolic junction, gas is seen in the cecum and more gas-filled loops of intestine are seen on serial radiographs and the patient is treated medically. If the obstruction is not moving, as determined by serial radiographs, then the case becomes surgical. If the rabbit is taken to surgery it is ideal to try and gently milk the obstruction down through the ileocolic junction and into the hind gut instead of performing an enterotomy due to thin and friable nature of the rabbit small intestine.

Depending on the severity of the condition and clinician discretion a variety of treatment measures may include:
     • Abdominal massage: Gentle, deep massage of the abdomen to stimulate intestinal contractions and to break down impacted stomach contents. If diagnosed early in the course of the disease; encourage movement and exercise as a way to stimulate gut motility.
     • Fluid therapy in appropriate amounts and properly administered.
     • Analgesics as needed; if showing signs of pain or if evidence of increased GI gas.
     • Syringe feeding an enteral nutrition product such as Oxbow Critical Care in order to provide nutritional supplementation and fiber to stimulate GI motility. Nasogastric (NG) tube placement has been advocated in the treatment of GI stasis with one paper showing that nutritional support through a 5- to 8- Fr Argyle tube (Kendall, Mansfield, MA), passed ventrally and medially into the ventral nasal meatus and advanced to the stomach, not only provided for nutritional support but also helped stimulated gastrointestinal motility and early return to function.
     • Appetite stimulants: The sooner the rabbit eats the sooner the intestinal motility will return to normal. Vitamin B complex injections or 1-4mg/rabbit PO q12-24h cyproheptadine (Periactin®, Merck,West Point, PA) may act to stimulate the appetite.
     • GI motility stimulants: Prokinetics such as cisapride (available through a compounding pharmacy) dosed at 0.5mg/kg PO q8-12h and metoclopromide (Reglan®, Schwarz Pharm. Mequon, WI) at 0.5mg/kg PO,SC q8-24h.
     • Simethicone: To help break down gas bubbles associated with bloating.
     • If suspect endotoxin-induced gut mucosal injury consider epidural analgesia to prevent functional and structural mucosal alterations.