SUPPLEMENTAL DIETARY-FAT AND RUMINALLY PROTECTED AMINO-ACIDS FOR LACTATING JERSEY COWS

Eight Jersey cows receiving a 50:50 ratio of forage to concentrate on a DM basis were used in a replicated 4 x 4 Latin square design to dete rmine the effects of added fat (3.4% of dietary DM) and ruminally prot ected AA (8 g of Met and 24 g of Lys daily) on yield and composition o f milk. Treatments were 1) basal control, 2) added fat, 3) added AA, a nd 4) fat plus AA. Compared with no added fat, fat supplementation inc reased 4% FCM yield (24.7 vs. 23.0 kg/d) and milk fat yield (1.05 vs. .97 kg), depressed milk protein content (3.58 vs. 3.74%), and altered fatty acid composition of milk. Blood triglyceride and NEFA were eleva ted (34.4 vs. 29.5 mg/dl and 175.1 vs. 143.7 mu eq/L, respectively) by added fat. Supplementation with kA elevated blood Lys, Met, and urea N without increasing milk protein yield. Increase in blood NEFA was fu rther augmented by fat plus AA supplementation, but no changes in conc entrations of Lys or Met in blood were found. Addition of AA did not a lleviate the depression of milk protein content when supplemental fat was added to the diet for Jersey cows.