Journal of Animal Science, Vol 75, Issue 5 1415-1424, Copyright © 1997 by American Society of Animal Science

JOURNAL ARTICLE

Urea in dry-rolled corn diets: finishing steer performance, nutrient digestion, and microbial protein production

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

In Exp. 1, 88 yearling steers (332 kg) were fed dry-rolled corn finishing diets to evaluate effects of dietary urea level on performance and carcass characteristics. Diets contained 0, .5, 1.0, or 1.5% urea (DM basis), which supplied all supplemental N, and 10% chopped prairie hay. Gains (P = .10) and gain efficiency (G/F; P < .05) were increased by .5% urea, with little improvement by additional urea. Regression analysis estimated optimal dietary urea at .9% of DM for ADG and G/F. Fat thickness (P < .05) and yield grade (P < .10) increased linearly with dietary urea level. In Exp. 2, four ruminally and duodenally cannulated steers (557 kg) were fed the diets used in Exp. 1 to evaluate effects of dietary urea on site and extent of digestion. True ruminal OM and starch digestion were increased 25 and 37%, respectively, by .5% urea, but higher urea levels did not differ from .5%. Flows of total N and microbial N to the duodenum were not affected by urea level. In Exp. 3, 100 yearling steers (347 kg) were fed dry-rolled corn finishing diets that contained 10% alfalfa hay as the dietary roughage to evaluate effects of dietary urea level on performance and carcass characteristics. Urea levels were 0, .35, .70, 1.05, or 1.40% urea (DM basis), with no other supplemental N provided. Dry matter intake (P = .10), ADG (P < .05), and G/F (P < .05) increased with intermediate concentrations of urea but decreased with the highest concentration. Regression analysis indicated that the optimal dietary urea level was .5% of DM for ADG and G/F. Urea increased dietary energy utilization but not metabolizable protein supply.

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