Linseed oil supplementation to dairy cows fed diets based on red clover silage or corn silage: Effects on methane production, rumen fermentation, nutrient digestibility, N balance, and milk production.

The objective of this study was to examine the effect of linseed oil (LO) supplementation to red clover silage (RCS)- or corn silage (CS)-based diets on enteric CH4 emissions, ruminal fermentation characteristics, nutrient digestibility, N balance, and milk production. Twelve rumen-cannulated lactating cows were used in a replicated 4×4 Latin square design (35-d periods) with a 2×2 factorial arrangement of treatments. Cows were fed (ad libitum) RCS- or CS-based diets [forage:concentrate ratio 60:40; dry matter (DM) basis] without or with LO (4% of DM). Supplementation of LO to the RCS-based diet reduced enteric CH4 production (-9%) and CH4 energy losses (-11%) with no adverse effects on DM intake, digestion, ruminal fermentation characteristics, protozoa numbers, or milk production. The addition of LO to the CS-based diet caused a greater decrease in CH4 production (-26%) and CH4 energy losses (-23%) but was associated with a reduction in DM intake, total-tract fiber digestibility, protozoa numbers, acetate:propionate ratio, and energy-corrected milk yield. Urinary N excretion (g/d) decreased with LO supplementation to RCS- and CS-based diets, suggesting reduced potential of N2O emissions. Results from this study show that the depressive effect of LO supplementation on enteric CH4 production is more pronounced with the CS- than with the RCS-based diet. However, because of reduced digestibility with the CS-based diet, the reduction in enteric CH4 production may be offset by higher CH4 emissions from manure storage. Thus, the type of forage of the basal diet should be taken into consideration when using fat supplementation as a dietary strategy to reduce enteric CH4 production from dairy cows.