Supplemental dietary fat from extruded soybeans and calcium soaps of fatty acids for lactating cows.

Holstein cows (n = 33) were assigned to one of three diets containing soybean meal, supplemental fat from extruded soybeans, or supplemental fat from Ca soaps of fatty acids. Total mixed diets containing (DM basis) 25% corn silage, 25% alfalfa hay, and 50% of the respective concentrate mixtures were fed wk 4 through 15 postpartum. Milk production (29.2, 32.4, and 31.8 kg/d) was higher for cows fed supplemental fat diets. Milk protein percentages (2.99, 2.93, and 2.81) were higher for cows fed the soybean meal diet and were higher with extruded soybeans than with Ca soaps of fatty acids. Milk fat percentages (3.20, 2.69, and 3.47) were higher for cows fed Ca soaps of fatty acids than for cows fed extruded soybeans. Milk fat from cows fed supplemental fat was more unsaturated than from those fed soybean meal and was most unsaturated from cows fed extruded soybeans. Dry matter intakes (17.8, 18.4, and 16.6 kg/d) were not significantly different among diets. Extruded soybeans and Ca soaps of fatty acids were equally effective in increasing milk production, but milk fat content was reduced, and the proportion of unsaturated fatty acids in milk fat was increased, with extruded soybeans.