Effects of Dietary Energy Level and Supplemental Protein Source on Performance of Growing Steers and Nutrient Digestibility and Nitrogen Balance in Lambs

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Abstract
Four experiments were conducted to evaluate three crude protein (CP) sources (urea, U; soybean meal, SBM; corn gluten meal, CGM) in diets based on corn silage (high energy) or grass hay (low energy). In Exp. 1 and 2, growing steers were fed all combinations of energy and protein source at 10.5 or 12% CP. Steers fed high energy diets or 12% CP had improved (P<.05) daily gains and feed:gain over 84 d. Protein source had no effect (P>.05) on performance except that steers fed U consumed more (P<.05) feed than those fed CGM. Steers were fed experimental diets to a common weight and switched to an 85% concentrate diet for finishing. During finishing, steers fed low energy diets in the growing period consumed more (P<.05) feed and had increased (P<.05) feed:gain compared with those fed high energy diets. Growing lambs were fed the same diets as steers. At 10.5% CP, lambs fed high energy diets had higher (P<.05) digestibilities of dry matter (DM), organic matter (OM), nitrogen (N) and fiber components, and retained more (P<.05) N. For lambs on 12% CP, high energy diets had higher (P<.05) DM and OM digestibilities and lower (P<.05) N digestibilities. At 12% CP, energy level had no effect (P>.05) on N retained. Protein source had no effect (P>.05) on N retention. There appeared to be no advantage in supplementing with ruminally undegradable proteins, i.e. CGM, in these experiments. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science.