TRANSFORMATIONS AND EFFECTS OF LIPIDS IN THE RUMEN - 3 DECADES OF RESEARCH AT GENT-UNIVERSITY

A survey is given of research results on ruminant lipid digestion obta ined at the authors' laboratory. Results are presented in terms of lip id changes occurring in the rumen and in terms of effects on nature, e xtent and site of digestion. The rumen can be adapted to an extremely high capacity for triglyceride lipolysis, preferentially releasing pol yunsaturated fatty acids that are then further hydrogenated with accum ulation of oleic acid isomers in vitro only. Evidence was obtained for both microbial incorporation and synthesis of polyunsaturated acids. In vitro lipolysis is inhibited by pH values below 6.3 and by ionophor es. Free fatty acids inhibit methanogenesis with associated increases in propionate production and decreases in acetate and butyrate product ions; the latter being related to their defaunating effect. Both in th e faunated and defaunated rumen, free fatty acids decrease fibre diges tion, which is shifted to the hindgut, at least in sheep. Defaunation increases rumen microbial growth efficiency and may result in a higher duodenal flow of both feed and microbial protein, provided these incr eases are not overcome by a decreased apparent rumen OM digestibility. Considerable between animal variability exists for these effects, ass ociated with variable effects on rumen particle and liquid volumes and outflow rates.