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 hay:concentrate, 1:1.5) at a level of 48 g/kg DM, provided in C12:C14ratios of 5:0, 4:1, 3:2, 2·5:2.5, 2:3, 1:4 and 0:5. Additionally, an unsupplemented control consisting of the basal substrates only was employed. Incubation periods lasted for 15 (n4) and 25 (n2) d. CH4formation 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 C12:C14ratio of 4:1, whereas the second most effective treatment in suppressing CH4production (60 % relative to control) was found with a ratio of 3:2. Total methanogenic counts were decreased by those mixtures of C12and C14also successful in suppressing methanogenesis, the 4:1 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 ofMethanococcalesincreased andMethanobacterialesdecreased. Initially, CH4suppression 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 C12and C14in suppressing methanogenesis, mediated probably by direct inhibitory effects of the fatty acids on the methanogens.