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 acids were investigated using basal diets of extensive type (high structural carbohydrate content) and intensive type (low structural carbohydrate content). 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 oil in the diet did not clearly reduce methane release from the total digestive tract. In 2 in vitro experiments carried out with a RUSITEC apparatus, interactions of either coconut oil (Expt 2) or pure non-esterified lauric acid (Expt 3) with the 2 types of basal diet were determined using 2 × 2 factorial designs. Expt 2 confirmed a high efficacy of coconut oil against methane release in the intensive-type diet (suppression by 62% relative to control) and a reduced efficiency in the extensive-type diet (suppression by 6% relative to control). In contrast, pure lauric acid supplementation suppressed methane release in vitro by approximately 80%, and this was independent 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 develop effective feeding strategies against ruminal methane formation.