The natural diet of felids contains highly digestible animal tissues but also fractions resistant to small intestinal digestion, which enter the large intestine where they may be fermented by the resident microbial population. Little information exists on the microbial degradability of animal tissues in the large intestine of felids consuming a natural diet. This study aimed to rank animal substrates in their microbial degradability by means of an in vitro study using captive cheetahs fed a strict carnivorous diet as fecal donors. Fresh cheetah fecal samples were collected, pooled, and incubated with various raw animal substrates (chicken cartilage, collagen, glucosamine-chondroitin, glucosamine, rabbit bone, rabbit hair, and rabbit skin; 4 replicates per substrate) for cumulative gas production measurement in a batch culture technique. Negative (cellulose) and positive (casein and fructo-oligosaccharides; FOS) controls were incorporated in the study. Additionally, after 72 h of incubation, short-chain fatty acids (SCFA), including branched-chain fatty acids (BCFA), and ammonia concentrations were determined for each substrate. Glucosamine and glucosamine-chondroitin yielded the greatest OM cumulative gas volume (OMCV) among animal substrates (P < 0.05), whereas total SCFA production was greatest for collagen (P < 0.05). Collagen induced an acetate production comparable to FOS and a markedly high acetate-to-propionate ratio (8.41:1) compared to all other substrates (1.67:1 to 2.97:1). Chicken cartilage was rapidly fermentable, indicated by a greater maximal rate of gas production (R(max)) compared with all other substrates (P < 0.05). In general, animal substrates showed an earlier occurrence for maximal gas production rate compared to FOS. Rabbit hair, skin, and bone were poorly fermentable substrates, indicated by the least amount of OMCV and total SCFA among animal substrates (P < 0.05). The greatest amount of ammonia production among animal substrates was measured after incubation of collagen and rabbit bone (P < 0.05). This study provides the first insight into the potential of animal tissues to influence large intestinal fermentation in a strict carnivore, and indicates that animal tissues have potentially similar functions as soluble or insoluble plant fibers in vitro. Further research is warranted to assess the impact of fermentation of each type of animal tissue on gastro-intestinal function and health in the cheetah and other felid species.
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