Rumen biohydrogenation of n-3 polyunsaturated fatty acids and their effects on microbial efficiency and nutrient digestibility in sheep

The study examined the extent to which n-3 PUFA from different sources were biohydrogenated in the rumen and their effects on rumen microbial efficien cy and whole tract nutrient digestibility. Four ruminally and duodenally ca nnulated whether lambs were used in a 4 x 4 Latin square design. Four iso-e nergetic and iso-nitrogenous diets based on dried grass were formulated to provide similar fat levels (60 g/kg DM) from different sources; Megalac (pa lmitic acid. C16:0; Control), whole linseed (alpha -linolenic acid, C18:3n- 3; Linseed) fish oil (eicosapentaenoic acid, C20:5n-3, EPA and docosahexaen oic acids C22:6n-3, DHA; Fish oil) and whole linseed plus fish oil providin g equal amounts of oil (LinFish). Diets were offered at a rate of 1.2 kg/da y in 12 equal portions. Total fatty acid intake was similar on all diets whilst duodenal fatty acid flow varied between 101, 94, 87 and 90 % of dietary intake for animals fed the Control, Linseed, Fish oil and Linfish diets respectively. Duodenal fl ow of C18:3 n-3 in animals fed the Linseed diet was twice that of animals f ed the Control diet (P < 0.01)whilst animals fed the Fish oil diet had a si gnificantly greater flow of EPA and DHA than those fed any of the other die tary treatments. Duodenal flow of ri ans C18:1 in animals fed the Linfish d iet was significantly greater than that in animals fed either Linseed, Fish oil or Control diets (P < 0.001). Biohydrogenation of C18:3n-3 was 80 to 9 3 % in all diets whilst that of C20:n-3 and C22:6n-3 was 72 to 79 % in diet s that contained fish oil or linseed and fish oil. Apparent fatty acid dige stibility (duodenum to rectum) tended to be greater for unsaturated than sa turated fatty acids whilst whole tract Fatty acid digestibility (mouth to r ectum) was significantly greater in animals fed diets containing fish oil ( P < 0.05). All dietary n-3 PUFA sources decreased microbial protein synthes is and efficiency when expressed as either gN/kg organic matter (OM) appare ntly or truly degraded in the rumen. Additionally, the inclusion of fish oi l increased the proportion of propionate in the rumen whilst depressing the rumen digestibility of OM and fibre (P < 0.01), but had no significant eff ect on whole tract OM or fibre digestibility.