Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/2/2004
Publication Date: 7/25/2004
Citation: Vasconcelos, J.T., Greene, L.W., Cole, N.A., Mccollum, F.T. 2004. Effects of phase feeding of protein on performance, blood urea nitrogen, manure n:p ratio, and carcass characteristics of feedlot cattle [abstract]. Journal of Animal Science Supplement. 82(1):207
Technical Abstract: One hundred eighty four steers (BW = 406 kg) were used in a randomized block design to determine the effects of phase feeding of protein on performance, blood urea N (BUN), manure N:P ratio, and USDA carcass characteristics of feedlot steers. Steers were fed ad libitum a finishing diet containing 10% roughage (DM basis) formulated to contain 13% CP (DM basis). When steers reached 477 kg the diets were either maintained at 13% CP or reduced to 11.5% CP or no supplemental CP (approximately 10% CP). Reducing the CP to 11.5% or no supplemental CP did not affect (P = 0.21) ADG of steers (1.62, 1.71 and 1.53 kg/d for 13%, 11.5% or no supplemental CP, respectively) from day of diet change to day of harvest. The ADG of steers was similar (P = 0.09) throughout the finishing period regardless of level of CP treatment (1.69, 1.86, and 1.74 for approximately 10% CP, 11.5% CP and 13% CP, respectively). Similarly, dry matter intake and feed efficiency did not differ (P > 0.05) among treatments. BUN concentrations were determined (mg/dL) on d 1, day of the diet change, and immediately before harvest. Differences (P < .0001) in BUN were observed only immediately before the harvest. Animals fed the 13% CP diet had greater (P < .0001) BUN concentration (13.85 mg/dL) than animals fed the 11.5 % and no supplemental CP (12.08 and 10.04 mg/dL, respectively). Manure from the pen surface was collected and analyzed for N and P. No differences (P > 0.05) were observed in N (P = 0.60) and P (P = 0.93) concentrations among different treatments. The N:P ratio, however, was different (P = 0.038). The N:P ratio was 3.87, 3.45, and 3.56 in manure obtained from pens fed the 10% CP, 11.5% CP, and 13% CP diets, respectively. Carcass characteristics of steers did not differ (P > 0.1). Data indicate that under the condition of this study CP levels can be reduced during the final stages of finishing without effects on feedlot performance.