EFFECTS OF FEEDING HEAT-TREATED SOYBEANS AND NIACIN TO HIGH PRODUCING COWS IN EARLY LACTATION

Forty multiparous Holstein cows were assigned to a 2 × 2 factorial arrangement of treatments to compare heat-treated soybean meal and heat-treated whole soybeans as protein supplements and to measure the effects of 6 g of supplemental niacin/d. Treatments began 10 d prior to calving and continued through 15 wk postpartum. Dry matter intake was .9 kg/d more for cows fed heat-treated soybean meal than for those fed heat-treated soybeans. The latter diet contained about 2.5% more lipid, resulting in similar daily energy intakes of 34.3 and 33.6 Mcal NE1 for heat-treated soybean meal and heat-treated soybean diets. Niacin tended to improve DM intake of cows fed diets containing heat-treated soybeans. Milk production was not altered by treatments during the experimental period comprising the first 15 wk of lactation or during the following 15 wk when cows received a standardized diet. Milk fat percentage did not differ due to treatments. Milk protein percentage was lower for cows receiving the heat-treated soybeans without niacin compared with those receiving the heat-treated soybeans with niacin. Niacin did not effect milk protein percentage of cows fed heat-treated soybean meal. The protein supplement by niacin interaction suggests that niacin feeding corrected a dietary oil induced milk protein depression. Plasma glucose was significantly lower in cows fed heat-treated whole soybeans with or without niacin. Plasma nicotinamide was highest in the cows receiving supplemental niacin. Niacin tended to decrease plasma nonesterified fatty acid concentration in cows fed heat-treated soybeans but not in cows fed heat-treated soybean meal. © 1990, American Dairy Science Association. All rights reserved.