Fermentation Patterns in Rabbit Caecal Cultures Supplied with Plant Polysaccharides and Lactate

Marounek M. , S. 1. Vovk, V. Benda: Fermentation Pattems in Rabbit Caecal Cultures Supplied with Plant Polysaccharides and Lactate. Acta vet. Bmo 1997,67:9-13. Fermentation patterns were investigated in anaerobic cultures of the rabbit caecal contents supplied with starch, hemicellulose, pectin, inulin and sodium lactate. Pectin and inulin were fermented more rapidly than starch and hemicellulose. Fermentation of pectin produced the highest amount of fermentation gas. The highest molar proportion of acetate was found in volatile fatty acids (VFA) of cultures supplied with pectin or without substrate. The highest molar proportions of propionate, butyrate and caproate were found in cultures supplied with inulin, sodium lactate and starch, respectively. Acetate and butyrate accounted for 68 85 % of metabolite carbon. Low proportions of propionate and valerate were specific for all substrates. The production of methane was roughly proportional to the VFA production (one mol of methane per 5.9 -7.3 mols ofVFA). Hydrogen recovery values varied from 50.5 to 61.0 %, suggesting the presence of H2dependent acetogenesis. Rabbit, caecum, fermentation, VFA production, in vitro cultures The rabbit caecum is a fermentative chamber, where the microorganisms of the gut are able to metabolically alter the unabsorbed digesta from the stomach and small intestine, making it available to the host. The rabbit caecum is colonized by an abundant bacterial flora, ca 1010 cultivable cells per 1 g (Forsythe and Parker 1985). The principial substrates for caecal microorganisms are polysaccharides (hemicellulose, pectin, starch) and protein. Polysaccharides are converted to volatile fatty acids (VFA), methane, carbon dioxide and compounds incorporated into bacterial cells. The VFA are absorbed, supplying additional energy for the host. Broiler rabbits fed high concentrate diets are highly susceptible to the development of digestive disturbances. Weanling rabbits are particularly sensitive. High mortality of young rabbits has severe economic impact on commercial rabbit production. The ethiology of digestive disturbances is multifactorial. It is known, however, that apart from specific pathogenic agents, the proliferation in the caecum of bacteria that produce potent toxins is responsible for the major part of losses (Cheeke 1989). Cheeke and Patton (1980) proposed that enterotoxemia was caused by carbohydrate overload in the hindgut, providing a substrate allowing the proliferation of pathogens. On low fibre diets, hypomobility occurs, resulting in prolonged retention time of digesta in the caecum, changes in caecal pH, and ultimately causing changes in the caecal microbial population. On the other hand, it has been shown that caecal VFA and low pH inhibit pathogen's proliferation in the caecum (Prohaszka 1980). It follows from these facts that the caecal digestion is one of the factors limiting rabbit performance. The aim of this study was to obtain more information on rabbit caecal fermentation pattern. We compared production of microbial metabolites (VFA, gas, methane), in in vitro cultures of the rabbit caecal contents supplied with starch, hemicellulose, pectin, inulin and lactate.