Short communication: The effect of substituting fish oil in dairy cow diets with docosahexaenoic acid-micro algae on milk composition and fatty acids profile.

The effects of substituting fish oil (FO) with docosahexaenoic acid (DHA)-micro algae on milk chemical and fatty acid composition were examined in this study. Twenty-four Holstein cows in mid lactation grazing on an alfalfa-grass based pasture were divided into 4 treatment groups (6 cows/treatment) and supplemented with 7 kg/d grain mix plus 350 g of soybean oil and one of the following: 1) 150 g of FO, 2) 100 g of FO plus 50 g of algae, 3) 50 g of FO plus 100 g of algae, or 4) 150 g of algae. Cows were fed treatment diets for 3 wk, and milk samples were collected from each cow during the last 3 d of the study. Milk production (17.96, 17.56, 17.55, and 19.26 kg/d for treatment diets 1 to 4, respectively), milk fat percentages (3.17, 3.49, 3.74, and 3.43%), and milk protein percentages (3.35, 3.50, 3.71, and 3.42%) were similar between treatment diets. Concentrations (g/100 g of fatty acids) of milk cis-9 trans-11 (c9t11) conjugated linoleic acid (CLA; 3.41, 3.69, 4.47, and 4.21 for treatment diets 1 to 4, respectively) and vaccenic acid (11.80, 12.83, 13.87, and 13.53) were similar between treatment diets. Results of this study suggest that DHA-micro algae can partially or fully substitute FO in a cow's diet without any adverse effects on milk production, milk composition, or milk c9t11 CLA content. The DHA-micro algae may be used as a viable alternative for FO in cow's diet to modify rumen biohydrogenation to increase milk c9t11 CLA content.