Rabbit Fact Sheet - Digestion and Cecotrophy of the Rabbit
Digestion and Cecotrophy of the Rabbit
SUMMARY: Rabbits are simple-stomached animals that have adapted a specialized approach to effectively utilize their herbivorous diets. By mechanically separating indigestible from digestible material at the ileo- colic junction the rabbit is able to discard less valuable digesta in favor of more digestible. The less digestible material is excreted as “hard feces” and the remaining nutritionally concentrated digesta is swept into the cecum for fermentation. Night feces (cecotropes) from this cecal fermented material are packaged in mucin and pass through the colon to the anus. These cecotropes are ingested by the rabbit and swallowed intact where they contribute substantially to the protein, mineral and vitamin nutriture of the animal.
INTRODUCTION: Rabbits are non-ruminant (simple-stomached) herbivores. They have adapted a unique method of processing forage based diets that allow them to be nimble and yet nutritionally replete (Davies and Davies, 2003).
DIGESTION IN THE RABBIT: The rabbit has a cleft prehensile mouth that is well suited for grasping, sorting, and selecting grasses, leaves, and roots. Their dentition is reminiscent of
rodents with large incisors. But, most particle size reduction is done by the premolar/molar “cheek teeth” that masticate the food rapidly while mixing it with saliva. Along with adding moisture to the ingesta, the saliva contains both amylase and galactosidase enzymes, and contributes potassium and bicarbonate. Cecotropes, unlike newly ingested food are not masticated and remain intact as mucin coated pellets.
Upon swallowing, the food is presented to the stomach, via the esophagus, and subjected to an HCl-pepsin digestion in very acidic (pH 1-2) conditions (Figure 1). The entry of this acid-chyme into the duodenum of the small intestine triggers the release of an entire cascade of hormones,
enzymes, and buffers. Small intestinal digestion for the rabbit is similar to that of other monogastric species, but transit time is very quick. Most digestion of simple proteins and fats occurs in the duodenum and jejunum, and the digestion/absorption of simple sugars occurs in the brush border region of the jejunum. The microbial protein of the cecotropes is digested in the jejunum and aided by the lysozyme that was added to the cecotropes in the colon and by enzymes from the cecotropes lysed bacterial cells. Electrolytes are absorbed (recycled) at or before the ileum.
DIGESTIVE TRACT OF THE RABBIT
Digesta exiting the ileum is mechanically separated by peristaltic/anti-peristaltic motions at the junction of the cecum and colon (Jenkins, 1999). Nutrient rich cecotropes (soft feces) are separated from “hard” feces that are high in indigestible fiber. The more nutrient dense fraction is swept into the cecum and fermented by a host of anaerobic bacteria. The hard feces are conveyed to the distal colon (anus) and excreted. After fermentation for 8 to 10 hours the “night” feces or cecotrophs are infused with lyso- zyme and coated with mucin by goblet cells in the fusis coli. This holds the cecotropes together and pro- tects them from degradation in the colon. As a bunch, the cecotrophs flow through the colon and arrive at the anus for direct ingestion.
This variation on the monogastric digestion process allows the rabbit to both discard indigestible materi- als rapidly, and to salvage the nutritive value derived from fermentation in the cecum. The nutrient compo- sition of cecotropes differ from hard feces with about half the crude fiber content, and appreciably more protein and essential amino acids (Carabano and Piquer 2003). Electrolyte minerals (K, Na, etc), and B-vitamins are also elevated in cecotropes (Table 1).
LITERATURE CITED:
• Carabano, R., and J. Piquer. 2003. The digestive system of the rabbit.
In: The Nutrition of the Rabbit. Edd C. de Blas and J. Wiseman. CABI Publishing, Oxon, UK pp 1-16.
• Davies, R.R., and J.E. Davies. 2003. Rabbit gastrointestinal physiology. Vet Clin Exot Anim 6 :139-153.
• Jenkins, J.R. 1999. Feeding Recommendations for the house rabbit. Vet Clin N Amer: Ex Anim Prac 2:143-151.
