Effects of supplementation of dairy cattle with fish oil on silage intake,milk yield and milk composition

The effects of level of fish oil inclusion in the diet on grass silage inta ke, and milk yield and composition of dairy cows offered either 5 or 10 kg concentrates/d were evaluated in a ten treatment, partly balanced, changeov er design experiment involving 50 cows in early lactation. Concentrates wer e prepared to provide 0, 150, 300 or +/-50 g fish oil/cow per d or 300 g fi sh oil/cow per d from a premix when each animal was offered 5 kg/d. The fis h oil was predominantly from herring and mackerel caught ill the North Atla ntic while the fish oil premix was obtained from a commercial source and us ed palm kernel expeller as a carrier. Increasing fish oil supplementation d ecreased silage dry matter intake and the concentrations of milk fat and pr otein, and increased milk yield and diet digestibility. There were signific ant interactions between concentrate feed level and level of fish oil for s ilage intake and milk yield. Other than for the concentrations of milk fat and protein, and 20:4n-6 fatty acids, the source of fish oil did not affect forage intake or animal performance. Fish oil supplementation also decreas ed the concentrations of milk protein by 0.9 g/kg for each 100 g increase i n fish oil supplementation, the depression being similar at each level of c oncentrate feeding. Supplementing the feed of dairy cows with 150 g fish oi l/cow per d decreased the concentration of milk fat by 15 g/kg. This study also she-wed that feeding dairy cattle with fish oil is an efficient method of increasing eicosapentaenoic acid in the human diet through transfer int o milk.