UNDEGRADED INTAKE PROTEIN - EFFECTS ON MILK-PRODUCTION AND AMINO-ACIDUTILIZATION BY COWS FED WHEAT SILAGE

Thirty-six Holstein cows in second or later lactation were used in a 6 3-d completely randomized block design to determine the effects of RUP source on milk production, composition, and estimated AA uptake by th e mammary gland. Cows were divided into 12 blocks of three cows each b ased on DIM (54.5 d) and milk production. Treatments were 1) soybean m eal; 2) treated SBM; and 3) supplemental protein from TSBM, corn glute n meal, and Menhaden fish meal with each protein supplying equal amoun ts of CP. Mean DMI was greater for cows fed supplemental RUP. Intake o f RUP was increased by 0.5 and 0.4 kg d(-1), respectively, for treatme nts 2 and 3. The NE(L) intake was greater for cows fed treatment 3 tha n for those fed treatment 2. RUP supplementation increased BW accretio n and milk production. Milk composition was unaffected except for lact ose, which was higher for milk from treatment 3 than for milk from tre atment 2. Extraction efficiencies of AA indicated that the supply of M et and Lys to the mammary gland was first and second limiting for cows receiving treatments 1 and 2 but colimiting for cows fed treatment 3. Results indicate performance differences related to RUP sources and s pecifically the amounts of Lys and Met available for metabolism.