Comparative efficiency of various fats rich in medium-chain fatty acids tosuppress ruminal methanogenesis as measured with RUSITEC

A RUSITEC apparatus equipped with eight fermenters was used to investigate the effects of seven different fats with high proportions of medium-chain f atty acids (C-8:0-C-16:0) supplied at a level of 53 g kg(-1) DM. In detail, coconut oil, palm kernel oil, palm oil, tallow, milk fat and two types of canola oils, both genetically enriched with lauric acid, were compared with a diet supplemented with prilled fat. The prilled fat was selected from th ree different rumen-protected fats in a preliminary experiment as the least effective one regarding methane release. Palm kernel oil, coconut oil and one of the canola oils significantly (P < 0.05) decreased methane release, methanogens and ciliates whereas the other fats had only minor effects. Wit h the use of the three effective fats, NDF degradation was also suppressed (P < 0.05), but the rumen fluid concentration of volatile fatty acids remai ned unchanged. However, at constant acetate proportion, butyrate proportion increased (P < 0.05) at the expense of propionate. Apart from a high propo rtion of lauric and myristic fatty acids in the fatty acid composition, com plete melting at rumen fluid temperature seems to support the ability of so me fats to reduce methanogenesis and to suppress methanogens and ciliates.