Effects of feeding unprocessed oilseeds on methane emission, nitrogen utilization efficiency and milk fatty acid profile of lactating dairy cows

Lipid supplementation can decrease enteric methane emission and affect nutrient utilization in dairy cows. The objective of this study was to evaluate the effects of dietary inclusion of unprocessed oilseeds on methane emissions, nitrogen (N) utilization efficiency, and milk fatty acid (FA) profile of dairy cows. Eight multiparous Holstein Friesian cows (75.4 ± 15.9 days in milk) were randomly allocated to treatments in a double 4 × 4 Latin square with 4 periods (22 d for adaptation and 6 d for measurements in digestion units). Treatments formulated on an isonitrogenous and equal ether extract content were: 1) Prilled fat consisting of a mixture of FA from fractionated palm oil (PFA; 3.5% of diet DM), 2) Rapeseed (RPS; 6.9% of diet DM), 3) Cottonseed (CTS; 18.4% of diet DM), and 4) Linseed (LNS; 7.5% of diet DM). Oilseeds were fed without processing. Diets contained varying amounts of corn silage (26 to 27% of diet DM), grass silage (23 to 37% of diet DM), and concentrate (37 to 50% of diet DM), plus the allocated lipid source treatment. Diets were formulated to provide an ether extract level of 6% of diet DM. Methane emissions were measured using the SF6 technique. The RPS diet increased dry matter intake (DMI) compared to the other treatments. The CTS diet decreased methane production (g/d) and yield (g/kg of DMI) compared to RPS and LNS, and decreased methane intensity (g/kg of energy-corrected milk) compared to RPS, but not LNS or PFA. Also, the CTS diet increased N excretion in urine. Dietary inclusion of LNS and RPS decreased milk fat content, and the CTS diet tended to increase milk protein, and increased milk lactose contents compared to the PFA diet. However, milk yield and milk components yield were not affected by treatments. Unprocessed oilseeds improved milk FA profile by increasing mono- and poly-unsaturated FA concentration in milk fat. In conclusion, unprocessed oilseeds differed in their effects on the response variables studied, and many of these effects were independent of the degree of FA unsaturation. The most important implication of these results is the need to evaluate methane mitigation strategies in conjunction other environmental, production and consumer health aspects.