Effect of fish oil and high or low linolenic acid linseed or rapeseed on fatty acid composition of cow's milk

Twenty-eight Black-and-White cows were allotted to 7 groups (4 animals per group) and fed for 8 weeks a basal ration containing maize, lucerne, beet pulp silage, wet brewer's grain, meadow hay and different concentrate mixtures without additives (control group) or supplemented with 10% linseed (cv. Omega, Linola or Opal), rapeseed (cv. Spencer or Contact), or 4% fish oil as fat sources in the respective experimental groups. Each ingredient of the basal diet and concentrates was given separately. Cows fed diets enriched with vegetable oils produced more milk containing a somewhat lower level of fat, protein and lactose than control cows. Linseed cv. Omega or Opal increased n-3 PUFA, while linseed cv. Linola increased the proportion of n-6 PUFA in milk fat. Feeding diets supplemented with fat reduced the proportion of SFA and increased the proportion of CLA in milk fat, particularly when fish oil was fed.