EFFECT OF SOURCE AND AMOUNT OF SUPPLEMENTAL FAT ON LACTATION AND DIGESTION IN COWS

Thirty Holstein cows averaging 50 DIM were assigned to five dietary tr eatments for 75 d to determine the effects of source and amount of sup plemental fat on milk yield, milk composition, and nutrient digestibil ities. Diets were 1) control, 2) diet 1 plus 12% whole cottonseed, 3) diet 2 plus 2.2% safflower oil, 4) diet 2 plus 2.2% prilled tallow fat ty acids, and 5) diet 2 plus 4.4% prilled tallow fatty acids. Milk yie ld was increased an average of 2.1 kg/d by addition of 2.2% prilled ta llow fatty acids or safflower oil to the diet (7% fatty acids) contain ing 12% whole cottonseed. However, when fatty acids were increased to 9.1% with additional prilled tallow fatty acids, milk yield, DMI, and fatty acid digestibility decreased. Whole cottonseed alone and in comb ination with all fat additions decreased milk protein concentrations. Safflower oil increased C18:0, C18:1, and C18:2 fatty acids in milk. D igestibilities of OM, NDF, and ADF were not affected by diet. Suppleme ntation of a saturated or unsaturated fat source to increase fatty aci d content to 7.0% of dietary DM increased milk yield, but a further in crease in fat to 9.1% with the saturated source appeared excessive for cows yielding 30 to 35 kg/d of milk.