SUPPLEMENTAL FAT AND NICOTINIC-ACID FOR HOLSTEIN COWS DURING AN ENTIRE LACTATION

The objectives of this experiment were to determine long-term response s to supplemental fat (from whole soybeans and liquid animal fat) and to determine whether the supplementation of nicotinic acid would enhan ce milk protein content or yield. From wk 4 through 43 postpartum, 44 multiparous Holstein cows (10 to 12 per treatment) were assigned to on e of four dietary treatments: 1) control, 2) control plus 12 g/d of ni cotinic acid, 3) supplemental fat, and 4) supplemental fat plus 12 g/d of nicotinic acid. The dry matter intake of cows did not differ among dietary treatments. Yields of milk, solids-corrected milk, and 3.5% f at-corrected milk were increased by nicotinic acid; the yield of fat-c orrected milk during wk 4 to 25 was increased by supplemental fat. Con tents of crude protein (CP) and true protein in milk were less for cow s fed diets supplemented with fat or nicotinic acid; casein content wa s decreased by nicotinic acid. Intake of net energy for lactation was greater for cows fed supplemental fat; energy balance was greater duri ng wk 4 to 25 for cows fed diets supplemented with fat. Body condition score and body weight were less when nicotinic acid was added to the control diet than when it was added to the diet supplemented with fat. Supplemental fat increased the concentration of nonesterified fatty a cids (NEFA) in plasma; nicotinic acid increased NEFA when it was added to the control diet but decreased NEFA when it was added to the diet supplemented with fat. Nicotinic acid did not prevent the decrease in milk CP content that was induced by dietary fat, but it did increase m ilk yield and tended to increase the yield of milk CP.