Rumen simulation technique study on the interactions of dietary lauric and myristic acid supplementation in suppressing ruminal methanogenesis.

ABSTRACT

The interactions of lauric (C12) and myristic acid (C14) in suppressing ruminal methanogenesis and methanogens were investigated with the rumen simulation technique (Rusitec) using bovine ruminal fluid. The fatty acids were added to basal substrates (grass hayconcentrate, 11.5) at a level of 48 g/kg DM, provided in C12C14 ratios of 50, 41, 32, 2.52.5, 23, 14 and 05. Additionally, an unsupplemented control consisting of the basal substrates only was employed. Incubation periods lasted for 15 (n 4) and 25 (n 2) d. CH4 formation was depressed by any fatty acid mixture containing at least 40 % C12, and effects persisted over the complete incubation periods. The greatest depression (70 % relative to control) occurred with a C12C14 ratio of 41, whereas the second most effective treatment in suppressing CH4 production (60 % relative to control) was found with a ratio of 32. Total methanogenic counts were decreased by those mixtures of C12 and C14 also successful in suppressing methanogenesis, the 41 treatment being most efficient (60 % decline). With this treatment in particular, the composition of the methanogenic population was altered in such a way that the proportion of Methanococcales increased and Methanobacteriales decreased. Initially, CH4 suppression was associated with a decreased fibre degradation, which, however, was reversed after 10 d of incubation. The present study demonstrated a clear synergistic effect of mixtures of C12 and C14 in suppressing methanogenesis, mediated probably by direct inhibitory effects of the fatty acids on the methanogens.