Relative Value of Fish Meal Versus Solvent Soybean Meal for Lactating Dairy Cows Fed Alfalfa Silage as Sole Forage

Abstract

Fish meal was compared with soybean meal in three trials. In trial 1, 20 early lactation cows fed 70% alfalfa silage received an average .46kg of CP/d from either source in 2 × 2 Latin squares. Rumen protein escapes estimated in vitro were 37% (soybean meal) and 60% (fish meal). Fish meal increased BW gain, milk protein content, yield of milk, FCM, protein, and lactose; lowered rumen propionate; and increased rumen acetate:propionate. In trial 2, 32 midlactation cows fed 89% alfalfa silage were divided into two groups of 16 and supplemented with 0, 1.5, 3.0, or 4.5% CP from either soybean meal or fish meal in 4 × 4 Latin squares. Rumen protein escapes estimated in vitro were 31% (soybean meal) and 67% (fish meal). There were linear increases in BW gain and in yield of milk. protein, lactose, and SNF with either protein but no differences between proteins. In trial 3, 32 early lactation cows fed 56% alfalfa silage received no protein supplement or an average .55kg CP/d from soybean meal, high solubles fish meal, or low solubles fish meal in 4 × 4 Latin squares. Rumen protein escapes estimated in vitro were 27% (soybean meal), 43% (high solubles fish meal), and 63% (low solubles fish meal). Protein increased yield of milk, FCM, fat, protein, lactose, and SNF versus no supplement. Milk protein content increased about .1 percentage unit with both fish meals. Protein yield increased 61, 95, and 130 g/d with soybean meal, high solubles fish meal, and low solubles fish meal versus no supplement. In all trials, fish meal slightly reduced milk lactose content but did not alter milk fat content. Results indicated that greater rumen escape of fish meal protein, relative to soybean meal, increased efficiency of protein utilization in lactating cows fed alfalfa silage.