Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2006
Publication Date: 11/1/2006
Citation: Cole, N.A., Defoor, P., Galyean, M., Duff, G., Gleghorn, J. 2006. Effects of phase-feeding of crude protein on performance, carcass characteristics, serum urea nitrogen concentrations, and manure nitrogen of finishing beef steers. Journal of Animal Science. 84:3421-3432. Interpretive Summary: Environmental issues are a growing concern among cattle feeders and the general public. Large cattle feeding operations can potentially have adverse effects on local air quality via generation of dusts and odors. Significant quantities of ammonia may also be emitted from feedyards. Emissions of ammonia, although a possible contributor to local odor concerns, are actually a regional concern because the ammonia may travel longer distances are deposit on nutrient sensitive ecosystems or combine with auto and industrial fumes to produce small particulates that may have adverse effects on human health. Thus it is important that we develop nutritional and management regimens that can decrease ammonia emissions without having adverse effects on animal performance or economics of production. As cattle mature their dietary protein requirement, as a percentage of the diet decreases. Thus, decreasing the dietary CP concentration during the latter part of the finishing period (termed phase feeding) might decrease feed costs and N losses to the environment. We conducted a study with three hundred eighteen medium-framed crossbred steers (average starting weight of 315 + 4.9 kg) fed 90% (DM basis) concentrate, steam-flaked corn-based diets to evaluate the effects of phase feeding of CP on performance and carcass characteristics, manure characteristics and potential ammonia emissions from feedyards. In this study phase feeding of protein tended to have adverse effects on animal performance; however, total nitrogen excretion was decreased 1.5 to 4 kg/steer and estimated ammonia emissions were decreased by 3 to 5 kg/steer (20 to 25%). Results suggest that decreases in dietary CP concentration in the latter portion of the feeding period may have modest effects on overall beef cattle performance, but produce beneficial environmental effects.
Technical Abstract: As cattle mature the dietary protein requirement, as a percentage of the diet decreases. Thus, decreasing the dietary CP concentration during the latter part of the finishing period might decrease feed costs and N losses to the environment. Three hundred eighteen medium-framed crossbred steers (315 + 4.9 kg) fed 90% (DM basis) concentrate, steam-flaked corn-based diets were used to evaluate the effect of phase feeding of CP on performance and carcass characteristics, serum urea N concentrations, and manure characteristics. Steers were blocked by BW and assigned randomly to 36 feedlot pens (eight to10 steers per pen). After a 21-d step-up period, the following dietary treatments (DM basis) were assigned randomly to pens within a weight block: 1) 11.5% CP diet fed throughout; 2) 13% CP diet fed 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 when approximately 60% of the cattle within a weight block were visually estimated to grade USDA Choice. On average, the cattle were fed for 182 d. Cattle switched from 13% to 10% CP diets with 56 d left on feed or from 13 to 11.5% CP with only 28 d left on feed had lower (P < 0.05) ADG, DMI, and G:F than steers fed a 13% CP diet throughout. Steers on the phase-feeding regimens had lower (P = 0.05) ADG and DMI during the last 56 d on feed than steers fed 13.0% CP diet throughout. Carcass characteristics were not affected by dietary regimen. Performance by cattle fed a constant 11.5% CP diet did not differ from those fed a 13% CP diet, although cattle fed the lower CP diet had numerically lower overall ADG (1.42 vs.1.46 kg: P = 0.38) and DMI (7.64 vs. 7.96 kg: P = 0.16) during the feeding period. Serum urea N concentrations increased (P < 0.05) with increasing dietary CP concentrations. Phase feeding decreased estimated N excretion by 1.5 to 3.8 kg/steer and ammonia volatilization losses by 3 to 5 kg/steer. 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% of DM would adversely affect performance of cattle fed high-concentrate, steam-flaked corn-based diets.