EFFECTS OF ADDED DIETARY-FAT AND AMINO-ACIDS ON PERFORMANCE OF LACTATING COWS

The objective of this trial was to determine whether the effect of add ed dietary fat to reduce milk protein percentage could be modified by Met and Lys sources that escape ruminal degradation Holstein cows were assigned to treatments of 1) control diet; 2) 3.5% added fat (whole c ottonseeds and Ca salts of long-chain fatty acids); 3) added Met (6.6 g/d) as Zn Met and Lys (8.2 g/d) as Zn Lys; and 4) combination of adde d fat, Met (5 g/d), and Lys (6.2 g/d). Cows were fed these diets for 1 6 wk. Milk yield was recorded daily and averaged by week, and composit ion was determined on samples taken monthly. Milk yield was increased significantly by the added AA. The percentage of total CP in milk was reduced by the added dietary fat and unaffected by the added AA. Perce ntage of milk fat was unaffected by treatment, but yield of milk fat w as increased by the AA. Additional analyses were conducted on milk sam ples collected during wk 12 to determine the concentration of N in cas ein, whey, and urea fractions. Percentages of casein N, whey N, and ur ea N were not significantly affected by treatment. The concentration o f Zn in milk and whey was not changed by treatment, nor were there cha nges in plasma Zn, Cu, Ca, P, or urea N. Yields of FCM, protein, and f at were increased by the added dietary AA.