EFFECTS OF INTRAPERITONEAL L-LEUCINE, L-ISOLEUCINE, L-VALINE, AND L-ARGININE ON MILK-FAT DEPRESSION IN EARLY LACTATION COWS

Eight Holstein cows were assigned following calving to two groups, bal anced for parity, using a continuous completely randomized block desig n. Cows were fed a diet with 13.5% CP and 22.4% ADF from 35 to 55 DIM and then 13.8% CP and 15% ADF from 56 to 92 DIM. Alfalfa grass hay was the forage source, and concentrate mixtures contained primarily com a nd soybean meal. Cows were given daily intraperitoneal infusions of a solution of L-Leu (46.1 g, 84.2 mM), L-Ile (31.4 g, 57.3 mM), L-Val (3 8.3 g, 78.2 mM), and L-Arg (25.0 g, 34.4 mM) or physiological saline f ollowing the a.m. milking from 42 through 84 DIM. Infusion of AA signi ficantly increased plasma concentrations of Leu, Ile, Val, and Arg. Ef fects of AA infusion occurred during the low fiber period. Cows receiv ing AA maintained daily milk fat yield, increased p.m. milk fat yield, decreased less in p.m. milk fat percentage, and increased daily and p .m. yields Of C-16 fatty acids in milk. During the posttreatment perio d, cows previously receiving AA declined in daily milk fat yield, milk fat percentage, and total daily C4 to C-16 milk fatty acid yield. Res ults suggest that the infused AA may have increased de novo synthesis Of C-16 milk fatty acids.