Yield response of lactating Holstein dairy cows to dietary fish meal or meat and bone meal

Experiments were conducted to examine the effects of the source and amount of dietary protein on yield and composition of milk from Holstein dairy cows. Study 1 used 36 multiparous cows at 125 +/- 59 d in milk in a replicated 2 x 2 Latin square design. Treatments were diets formulated to contain 16% crude protein (CP) in which 11% was fish meal or meat and bone meal supplied 11% of dietary CP. Intakes of dry matter, CP, and net energy for lactation; yields of milk; and percentage of milk fat were not affected by treatment. Fish meal increased contents of milk total N, casein N, and noncasein N but did not increase contents of NPN; fish meal also tended to increase milk CP yields. Study 2 used 78 cows (31 primiparous) at 31 +/- 2 d in milk in a randomized block design. Two treatment diets were formulated to contain 16 or 18.5% CP, and soybean meal was the sole source of supplemental protein in those diets. The two other treatment diets were formulated to contain 16% CP; in these diets, fish meal or meat and bone meal partially replaced soybean meal. Treatments did not influence yield or composition of milk from multiparous cows. Compared with a soybean meal diet containing 16% CP, a soybean meal diet containing 18.5% CP or diets containing 16% CP and containing meat and bone meal or fish meal increased the milk yield of primiparous cows similarly. Fish meal or meat and bone meal increased the efficiency of protein utilization for milk yield.