Effects of Added Dietary Fat and Amino Acids on Performance of Lactating Cows

¹ Animal Sciences Department, Washington State University, Pullman 99164-6320

The objective of this trial was to determine whether the effect of added 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 cottonseeds 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 added fat, Met (5 g/d), and Lys (6.2 g/d). Cows were fed these diets for 16 wk. Milk yield was recorded daily and averaged by week, and composition 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. Percentage of milk fat was unaffected by treatment, but yield of milk fat was increased by the AA. Additional analyses were conducted on milk samples collected during wk 12 to determine the concentration of N in casein, whey, and urea fractions. Percentages of casein N, whey N, and urea N were not significantly affected by treatment. The concentration of Zn in milk and whey was not changed by treatment, nor were there changes in plasma Zn, Cu, Ca, P, or urea N. Yields of FCM, protein, and fat were increased by the added dietary AA.

Key Words: cows • lactation • fat • zinc

Submitted on September 28, 1992
Accepted on January 19, 1993