Milk fatty acid composition for indoor and grazing dairy cows when supplemented with a blend of fish and linseed oils

The objective of this study was to investigate the effect of fish oil (FO) and linseed oil (LO) supplementation on milk fatty acids (FA) composition, conjugated linoleic acid (CLA) in particular, for dairy cows managed under an indoor or outdoor grazing feeding system. Eighteen lactating Holstein cows were randomly assigned to one of two treatment groups: indoor cows with free access to corn silage and alfalfa hay plus 10 kg/d grain mix supplementation containing 700 g LO and 300 g FO (FOLO) or grazing cows with free access to grass pasture plus 10 kg/d grain mix supplementation containing 700 g LO and 300 g FO (FOLOP). Cows fed treatment diets for 21 days and milk samples were taken from each cow during the last 3 days of the study. Milk production, milk protein percentages and milk protein yield were not affected by treatment diets. Milk fat percentages (2.77 and 2.31 for the FOLO and FOLOP, respectively) and yield (0.93, and 0.81 kg/d) were lower with the FOLOP diet. Concentrations of milk c9t11 CLA (1.77, and 2.94 g/100g FA) and vaccenic acid (VA; 5.07, and 7.17 g/100g FA) were higher with the FOLOP diet. However, concentration of milk t10 C18:1 (4.08 and 2.35 g/100g FA) was higher with the FOLO diet. In conclusion, the increase in milk c9t11 CLA content was greater when oil supplementation was combined with grazing. The lower c9t11 CLA concentration in milk from the indoor fed cows resulted from t10 C18:1 replacing VA as the predominant trans C18:1 isomer.