Enteric methane production, digestibility and rumen fermentation in dairy cows fed different forages with and without rapeseed fat supplementation

The purpose of this experiment was to study the effect of forage species (grass or maize) and the maturity stage of grass on enteric methane (CH4) production, nutrient digestibility and rumen fermentation, and to study possible interactions with cracked rapeseed as fat source. Six lactating, ruminal, duodenal and ileal cannulated Holstein dairy cows (206 days in milk, milk yield 25.1 kg) were submitted to an incomplete Latin square design (6 × 4) with six diets and four periods. Two grass silages (early first cut, 361 g aNDFom/kg DM and late first cut, 515 g aNDFom/kg DM) and one maize silage were supplemented with either low fat concentrate or high fat concentrate. The dietary fat concentration in the high fat diets was approximately 60 g/kg DM. Diurnal samples of duodenal and ileal digesta and feces were compiled. The CH4 production was measured for four days in open-circuit respiration chambers. Additional fat reduced the gross energy (GE) lost as CH4 from 6.3 to 5.8% of GE intake, independent of forage species and quality. Energy loss as CH4 constituted 6.1, 6.7 and 5.4% of GE intake for early grass silage, late grass silage and maize silage, respectively. However, there was no difference between early grass silage and maize silage when CH4 production was related to kg organic matter (OM) digested. Fat supplementation did not affect OM or aNDFom digestibility. Maize silage had a higher ruminal OM digestibility, but lower ruminal aNDFom digestibility than grass silage. Early cut grass silage had a higher total tract OM and aNDFom digestibility than late cut grass silage. The present study demonstrates that choice of forage species and harvest time affects CH4 emission from dairy cows, while the CH4 reducing ability of fat does not interact with forage characteristics.