Journal of Animal Science, Vol 75, Issue 10 2813-2823, Copyright © 1997 by American Society of Animal Science

JOURNAL ARTICLE

Effects of dietary nitrogen source and concentration in high-grain diets on finishing steer performance and nutrient digestion

C. T. Milton, R. T. Brandt Jr and E. C. Titgemeyer
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506, USA.

Two experiments were designed to evaluate dietary N source and concentration on finishing steer performance and nutrient digestion. In Exp. 1, 100 steers were used in a randomized complete block design experiment with 2 x 2 + 1 factorially arranged treatments. Diets contained 1.93 or 2.24% N supplemented by urea or soybean meal (SBM), or 2.24% N supplemented by cottonseed meal (CSM). Steers fed SBM-supplemented diets gained 13% faster (P < .01) and were 9% (P < .01) more efficient converting feed to gain than steers receiving urea. Steers fed diets containing 2.24% N were 4% (P < .05) more efficient than those fed diets containing 1.93% N. Steers fed CSM-supplemented diets gained 6% (P < .10) less efficiently than steers receiving SBM. Increasing dietary N with urea from 1.93 to 2.24% decreased carcass weights 3%, whereas increasing dietary N with SBM increased carcass weights 3%. Carcass-adjusted gains were reduced 8% by increasing urea from .9 to 1.5% but increased 7% by increasing SBM from 6.1 to 10.5% of DM. In Exp. 2, four ruminally and duodenally cannulated steers (390 kg) were used in a 4 x 4 Latin square design experiment to evaluate urea and SBM supplementation on digestion. Diets contained no supplemental N, 1.84% N with urea or SBM as the supplement, or 2.16% N with SBM as the supplement. Total tract starch digestion, duodenal microbial N flow, and efficiency of microbial protein synthesis in the rumen were higher (P < .10) in steers fed SBM- than in those fed urea-supplemented diets. Supplementation with SBM increased metabolizable protein supply and dietary energy utilization.

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