One hundred sixty eight 12 to 13 month-old steers weighing 740 lbs were allotted to 28 pens. Seven pens were allotted to each of four programs for providing supplemental protein. The programs were I: Continuous supplementation with soybean meal (12.4% crude protein), II: Continuous supplementation with urea (11.7% crude protein), III: Feeding supplemental soybean meal (12.4% crude protein) and changing to urea supplementation (11.7% crude protein) at 42 days and IV: Feeding supplemental soybean meal (12.4% crude protein), changing to urea (11.7% crude protein) at 42 days followed by decreasing the concentration of supplemental urea (10% crude protein) at 84 days. During the first 42 days, Programs I, III and IV provided adequate metabolizable protein and ruminally available nitrogen and Program II provided adequate ruminally available nitrogen but inadequate metabolizable protein. During the period from 42 to 84 days all programs provided adequate ruminally available nitrogen and metabolizable protein in excess of requirement. Metabolizable protein was provided in greater excess during the final period of 84 to 135 days by Programs I, II and III. Program IV was designed to provide ruminally available nitrogen at 80% of predicted needs during the final stage of finishing. During the final period, Program IV provided metabolizable protein in excess of requirement but less than the other three programs. Steers fed the diet containing soybean meal during the first period gained more and were more efficient than those fed urea. There were no differences in performance among programs during the second and third periods. Overall steers fed soybean meal tended to have increased gain and improved feed efficiency. These results indicate finishing steers can be fed less supplemental protein during the final stages of finishing and be fed less ruminally available nitrogen than predicted needs without affecting feedlot performance. Carcasses averaged 79% low Choice or better and were 68% yield grade 1 and 2. Other than weight, carcass measurements were not affected by the programs to furnish supplemental protein. Total feed costs were decreased by reducing supplemental protein as the steers finished, but the greatest benefit was reduction in nitrogen excretion; 5.4 and 2.5 lbs nitrogen/steer in Program IV compared with Programs I and III, respectively. The results of this experiment indicate it is possible to reduce the environmental impact of feedlot cattle on the environment by program feeding of supplemental protein.
Iowa State University
Trenkle, Allen H. and Barrett, K., "Feedlot Performance of Cattle Program Fed Supplemental Protein" (2003). Beef Research Report, 2003. 15.