NUTRITION, FEEDING, AND CALVES Dry Matter Intake, Milk Yield and Composition, and Nitrogen Use in Holstein Cows Fed Soybean, Fish, or Corn Gluten Meals 1

Soybean meal, Atlantic menhaden fish meal, and corn gluten meal feeds varying in CP degradability and amino acid pat­ tern were evaluated as supplements for high milk yield. Forty multiparous Hol­ stein cows were fed a basal diet of corn silage:grain (blended, .8% urea, 12% CP, DM basis) ad libitum in wk 1 to 18 of lactation. During wk 1 to 3 of lactation, diet DM was 16% CP (basal plus soy­ bean, fish, and com gluten meals; each source contributed equal CP). On d 22, 10 cows were assigned to each of four diets: basal, 12% CP, OM basis or a diet containing 16% CP, OM basis with either soybean, fish, or corn gluten meal provid­ ing the supplemental CPo Cows readily ate all diets. Peak milk yields occurred later and were higher for cows fed soy­ bean (wk 8, 38.9 kg/d) and fish meals (wk 9, 41.6 kg/d) compared with those fed the basal diet (wk 4, 31.0 kg/d) or corn gluten meal (wk 5,37.5 kg/d). Milk protein yield was greater for cows fed soybean and fish meals. Fish meal decreased milk fat test (3.3 to 2.8%);