Effects of Feeding Heat-Treated Soybeans and Niacin to High Producing Cows in Early Lactation

Forty multiparous Holstein cows were assigned to a 2 x 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 .9kg! 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 NEI for heat-treated soybean meal and heattreated soybean diets.Niacin tended to improve OM 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