UREA IN DRY-ROLLED CORN DIETS - FINISHING STEER PERFORMANCE, NUTRIENTDIGESTION, AND MICROBIAL PROTEIN-PRODUCTION

In Exp. 1, 88 yearling steers (332 kg) were fed dry-rolled corn finish ing 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 ha y. Gains (P = .10) and gain efficiency (G/F; P < .05) were increased b y .5% urea, with little improvement by additional urea. Regression ana lysis 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 cannulat ed steers (557 kg) were fed the diets used in Exp. 1 to evaluate effec ts of dietary urea on site and extent of digestion. True ruminal OM an d starch digestion were increased 25 and 37%, respectively, by .5% ure a, but higher urea levels did not differ from .5%. Flows of total N an d 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 di ets that contained 10% alfalfa hay as the dietary roughage to evaluate effects of dietary urea level on performance and carcass characterist ics. Urea levels were 0, .35, .70, 1.05, or 1.40% urea (DM basis), wit h 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 analy sis indicated that the optimal dietary urea level was .5% of DM for AD G and G/F. Urea increased dietary energy utilization but not metaboliz able protein supply.