Lactational response of dairy cows to increased dietary crude protein with added fat.

Thirty-six Holstein cows were assigned to one of three diets containing soybean meal (16% CP), added fat from extruded soybeans (16% CP), and added fat and protein from extruded soybeans plus soybean meal (18% CP) to determine whether feeding additional protein would prevent the depression in milk protein percentages usually experienced when cows are fed additional fat. Total mixed diets containing 25% corn silage, 25% alfalfa hay, and 50% of respective concentrate mixtures were fed individually wk 4 through 16 postpartum; pretreatment (wk 3 postpartum), milk production, and composition data were used as covariates. Milk production (33.0, 35.8, and 34.2 kg/d) was higher for cows fed added fat. Milk protein (2.92, 2.88, and 2.83%) and casein (2.16, 2.13, and 2.09%) tended to decrease for cows fed added fat and did not increase with higher dietary protein. Dry matter intakes (20.9, 20.7, and 19.8 kg/d) and BW were similar for all diets. Supplementing additional CP to a diet containing added fat did not prevent depression in milk protein percentage.