Production, composition and antioxidants in milk of dairy cows fed diets containing soybean oil and grape residue silage

Four primiparous Holstein cows averaging 504 kg of body weight and 136 days in milk were used in a 4×4 Latin square design with four 21 days experimental periods to determine the effects of feeding four concentrations (0, 50, 75 and 100 g/kg of dry matter (DM)) of grape residue silage on DM intake, total tract apparent digestibility (TTAD), milk production, milk composition, milk fatty acid profile and milk concentration of antioxidants when cows were fed a diet containing soybean oil. Intake of DM and nutrients was similar among diets, except for intake of ether extract (EE) which increased with the proportion of grape residue silage in the diet. The TTAD of DM, crude protein (CP), EE, acid detergent fiber and neutral detergent fiber decreased linearly with higher proportions of grape residue silage in the diet. Milk production and concentrations of CP, fat and lactose were similar among treatments, but increased levels of grape residue silage reduced milk urea N content. There was a little effect of diet on milk fatty acid composition, although there was a trend to increased proportion of polyunsaturated fatty acids in milk fat when feeding increased levels of grape residue silage. Concentrations of total polyphenols and flavonoids, and production of conjugated diene hydroperoxides in milk, were not altered by diets. Reducing power in milk was higher with increased dietary levels of grape residue silage. Results suggest that it is possible to improve milk fat quality by feeding cows with grape residue silage as shown by enhanced antioxidant activity, although it was clearly insufficient to overcome the negative effects on milk fat synthesis probably caused by the high levels of fat added to diets as soybean oil.