Energy utilization and milk fat responses to rapeseed oil when fed to lactating dairy cows receiving different dietary forage to concentrate ratio

We evaluated energy and N utilization, performance, milk fatty acid (FA) profile using grass silage-based diets when rapeseed oil (RO) was included in high- or low-forage diets. Four multiparous Nordic Red cows averaging 101 ± 16 days at the beginning of study were randomly assigned to a 4 × Latin square design with 2 factorial arrangement treatments. Each 21-d period consisted 14-d diet adaptation 7-d collection period. Cows fed following comprised total mixed rations based on silage forage concentrate (FC) ratio 35:65 65:35 containing 0 50 g/kg RO. Significant FC RO interactions observed for yield, protein lactose yields, fat concentration, proportions trans-11 18:1, trans-10 trans-10, cis-12 18:2, saturated FA. Feeding effective increasing yield compared high-forage diet, supplementation increased it further (P ≤ 0.01). A similar pattern yields lactose. Supplementing reduced concentration by 19% relative other without affecting yield. The proportion intake lost as urine decreased 0.05) balances. Nutrient intakes greater 0.01) whereas < protein, starch, fiber intakes. Methane production, expressed intake, this variable declined similarly both 18:1 CLA but not diet. However, trans FA proportions, even though changes more profound In addition, cis monounsaturated Overall, had lower methane emissions partitioning towards secretion influencing According results, did compromise nutrients 150 could be preferentially used improve production quality accompanied reduction loss.