SOYBEANS VERSUS ANIMAL SOURCES OF RUMEN-UNDEGRADABLE PROTEIN AND FAT FOR EARLY LACTATION DAIRY-COWS

Fifteen multiparous Holstein cows averaging 39 DIM were used in a repl icated 5 x 5 Latin square design to compare roasted soybeans and anima l byproducts as supplements for increasing the RUP content of lactatio n diets based on alfalfa. The control diet contained roasted soybeans and was formulated to meet requirements for RUP. Rumen-undegradable pr otein in the diet was increased by including additional roasted soybea ns or animal by-product proteins. To achieve diets with similar amount s of fat, we added tallow, hydrolyzed tallow fatty acids, or partially hydrogenated tallow to the control diet and to diets containing anima l by-product proteins. Control diets and diets with high RUP were esti mated to be 5.8 and 7.6% RUP (DM basis). The RDP of all diets was esti mated to be approximately 11.3% of DM. Milk yield was increased by add itional dietary RUP. Yield of FCM was greater for cows receiving anima l byproducts than for those fed additional roasted soybeans. Cows fed additional RUP yielded more milk protein, but milk protein percentage was decreased. Milk fat percentage was reduced by additional dietary R UP, but fat yield was not affected. Nutrient digestibility was greates t for diets containing animal byproducts. Cows fed tallow yielded more milk, FCM, and protein that did those fed hydrolyzed tallow fatty aci ds or partially hydrogenated tallow. Lactation performance can be enha nced by supplementing animal by-products or roasted soybeans to diets based on alfalfa and formulated to meet NRC recommendations for RUP.