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Department of Animal Sciences, Colorado State University, Fort Collins 80523-1171
1 Correspondence: phone: (970) 491-0668; fax: (970) 491-5326; Email: nirlbeck{at}ceres.agsci.colostate.edu.
Abstract
Rabbits are found in virtually every country in the world, providing protein, fiber, animal research, and companionship (third to dogs and cats). Because of an ability to utilize low-grain and highroughage diets, they have the potential to be a future protein source. Classified as an herbivorous nonruminant, rabbits have a simple, noncompartmentalized stomach along with an enlarged cecum and colon inhabited by a microbial population (primarily Bacteroides). Rabbits practice coprophagy, which enhances strategies of high feed intake (65 to 80 g/kg BW) and fast feed transit time (19 h), allowing rabbits to meet nutritional requirements. Coprophagy also increases protein digestibility (50 vs 75–80% for alfalfa). Feces are excreted on a circadian rhythm, and data indicate that the internal cycle differs when shifting from ad libitum to restricted feeding. Microbes digest cellulose (14% in rabbits vs 44% in cattle) in the hindgut of the rabbit, but the contribution of amino acids from microbial protein is thought to be minimal. Lysine and methionine may be limited in traditional diets, and urea is not utilized. Acetate is the primary microbial VFA, with more butyrate than propionate. Unlike ruminants, more VFA are produced on starch than on forage diets; however, VFA provide limited energy for maintenance. Fiber is essential to maintain gut health, stimulate gut motility (insoluble fiber only), and reduce fur chewing. Low-fiber diets result in gut hypomotility, reduced cecotrope formation, and prolonged retention time in the hindgut. High-starch diets may be incompletely digested in the small intestine due to rapid transit times, resulting in enteritis. Low-energy grains like oats are preferred. Low-protein concentrations increase cecotrope consumption and high levels decrease it. Finely ground feeds lead to enteritis, so a coarse grind is recommended. Rabbits have an unusual calcium metabolism, absorbing Ca without vitamin D facilitation; the excess calcium is excreted in the urine (parathyroid hormone and calcitonin regulate serum Ca levels). Diets high in Ca (alfalfa based) may result in kidney damage for animals at maintenance. Correct feeding management based on the idiosyncrasies of the rabbit gastrointestinal tract will maximize production for future meat production. A balanced diet containing adequate fiber (20 to 25%), minimal starch, and optimum protein concentration is the key to preventing gastrointestinal distress.
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