Response of Lactating Cows to Added Increments of Dietary Protein and Nonprotein Nitrogen

Abstract

Two 3 × 3 Latin square designs (12 cows per square, 4 weeks per period) measured the value of added increments of crude protein from soybean meal and urea in a high-urea basal ration. In the soybean meal square, all cows received rations which were 76.4% corn silage (34.1% dry matter), 18.8% of a 3.0% urea pelleted concentrate, and the remaining 4.8% was ground shelled corn in the basal ration, 2.4% ground shelled corn and 2.4% soybean meal in Soybean Meal 1, and 4.8% soybean meal in Soybean Meal 2. In the urea square, 2.4% ground shelled corn and 2.4% of a corn-urea mixture (87% ground shelled corn and 13% urea) were included in Urea 1 and 4.8% of the same corn-urea mixture in Urea 2. Soybean meal supplementation significantly increased milk production as compared with the basal treatment while urea supplementation showed no significant increase. Differences between Soybean Meals 1 and 2 were not significant. Cows in the soybean meal square produced more milk than those in the urea square (P < .025). Analysis of pooled data from both squares showed a significant depression in feed intake on the basal ration compared with the nitrogen-supplemented rations. In both squares plasma urea nitrogen increased linearly with crude protein (P < .005). Nitrogen retention and solids-not-fat percentages were increased with soybean meal supplementation (P < .01). © 1971, American Dairy Science Association. All rights reserved.