Undegraded intake protein: Effects on milk production and amino acid utilization by cows fed wheat silage

Thirty-six Holstein cows in second or later lactation were used in a 63-d completely randomized block design to determine the effects of RUP source on milk production, composition, and estimated AA uptake by the mammary gland. Cows were divided into 12 blocks of three cows each based on DIM (54.5 d) and milk production. Treatments were 1) soybean meal; 2) treated SBM; and 3) supplemental protein from TSBM, corn gluten meal, and Menhaden fish meal with each protein supplying equal amounts of CP. Mean DMI was greater for cows fed supplemental RUP. Intake of RUP was increased by 0.5 and 0.4 kg d(-1), respectively, for treatments 2 and 3. The NE(L) intake was greater for cows fed treatment 3 than for those fed treatment 2. RUP supplementation increased BW accretion and milk production. Milk composition was unaffected except for lactose, which was higher for milk from treatment 3 than for milk from treatment 2. Extraction efficiencies of AA indicated that the supply of Met 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 specifically the amounts of Lys and Met available for metabolism.