, 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.
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