Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 2/12/2005
Publication Date: 7/25/2005
Citation: Gleghorn, J.F., Defoor, P.J., Galyean, M.L., Duff, G.C., Cole, N.A. 2005. Influence of phase-feeding on performance of beef steers [abstract]. Journal of Animal Science Supplement. 88(1):368. Interpretive Summary:
Technical Abstract: As cattle mature the dietary protein requirement, as a percentage of the diet, tends to decrease; thus decreasing the dietary CP concentration during the latter part of the finishing period might decrease feed costs and N losses to the environment. This study evaluated the effect of phase feeding of CP on performance of finishing beef cattle fed 90% (DM basis) concentrate, steam-flaked corn-based diets. Three hundred sixty medium-frame cross-bred steers (315 + 4.9 kg) were blocked by BW and randomly assigned to 36 feedlot pens (10 steers per pen). Following a 21-day step-up period, the following dietary treatments (DM basis) were randomly assigned to pens within a weight block: 1) fed an 11.5% CP diet throughout; 2) fed a 13% CP diet throughout; 3) switched from an 11.5% to a 10% CP diet when approximately 56 d remained in the feeding period; 4) switched from a 13% to an 11.5% CP diet when 56 d remained; 5) switched from a 13% to a 10% CP diet when 56 d remained; and 6) switched from a 13% to an 11.5% CP diet when 28 d remained. Cattle were slaughtered by block when 60% of the cattle within a weight block were visually estimated to grade USDA Choice. On average, cattle were on feed for 182 d (161 d for Block 1, 183 d for Blocks 2 and 3, and 189 d for Blocks 4, 5, and 6. Cattle switched from 13% to 10% CP diets had lower (P <0.10) ADG (1.14 vs. 1.52 kg) and G:F (186 vs. 192 g/kg) than steers fed a 13% CP diet throughout. Steers on the phase-feeding regimens had numerically lower ADG and lower (P < 0.10) DMI during the last 41 days on feed than steers fed 11.5 or 13% CP diets throughout. Carcass characteristics were not affected by dietary regimen. Performance by cattle fed a constant 11.5% CP diet was similar to those fed a 13% CP diet, although cattle fed the lower CP diet had numerically lower overall ADG (1.48 vs.1.52 kg) and DMI (7.64 vs. 7.96 kg) during the feeding period. Results suggest that modest changes in dietary CP concentration in the latter portion of the feeding period may have modest effects on overall beef cattle performance, but that decreasing dietary CP to 10% would adversely affect performance of cattle fed high-concentrate, steam-flaked corn-based diets.