Urea in dry-rolled corn diets: finishing steer performance, nutrient digestion, and microbial protein production.
Milton C.T. | Brandt R.T. Jr. | Titgemeyer E.C.
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, 0.5, 1.0, or 1.5% urea (DM basis), which supplied all supplemental N, and 10% chopped prairie hay. Gains (P = 0.10) and gain efficiency (G/F; P < 0.05) were increased by 0.5% urea, with little improvement by additional urea. Regression analysis estimated optimal dietary urea at 0.9% of DM for ADG and G/F. Fat thickness (P < 0.05) and yield grade (P < 0.10) 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 0.5% urea, but higher urea levels did not differ from 0.5%. 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, 0.35, 0.70, 1.05, or 1.40% urea (DM basis), with no other supplemental N provided. Dry matter intake (P = 0.10), ADG (P < 0.05), and G/F (P < 0.05) increased with intermediate concentrations of urea but decreased with the highest concentration. Regression analysis indicated that the optimal dietary urea level was 0.5% of DM for ADG and G/F. Urea increased dietary energy utilization but not metabolizable protein supply.
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