Diet composition affects the level of ruminal methane suppression by medium-chain fatty acids

In 3 experiments, the methane-suppressing effects of medium-chain fatty aci ds were investigated using basal diets of extensive type (high structural c arbohydrate content) and intensive type (low structural carbohydrate conten t). In Expt 1, sheep were fed the extensive-type diet supplemented with 60 g/kg of rumen-protected fat (control) or coconut oil. The use of coconut oi l in the diet did not clearly reduce methane release from the total digesti ve tract. In 2 in vitro experiments carried out with a RUSITEC apparatus, i nteractions of either coconut oil (Expt 2) or pure non-esterified lauric ac id (Expt 3) with the 2 types of basal diet were determined using 2 x 2 fact orial designs. Expt 2 confirmed a high efficacy of coconut oil against meth ane release in the intensive-type diet (suppression by 62% relative to cont rol) and a reduced efficiency in the extensive-type diet (suppression by 6% relative to control). In contrast, pure lauric acid supplementation suppre ssed methane release in vitro by approximately 80%, and this was independen t of the basal-diet type used. The results suggest that interactions of fat with the basal diet in the rumen have to be taken into consideration to de velop effective feeding strategies against ruminal methane formation.