Effects of dietary protein concentration and ractopamine hydrochloride on performance and carcass characteristics of finishing beef steers

Authors: Hales Paxton, Kristin; Shackelford, Steven; Wells, James - Jim; King, David - Andy; PYATT, NATHAN - Elanco Animal Health, Inc; Freetly, Harvey; Wheeler, Tommy

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2016
Publication Date: 5/6/2016
Publication URL: http://handle.nal.usda.gov/10113/62564
Citation: Hales, K.E., Shackelford, S.D., Wells, J., King, D.A., Pyatt, N.A., Freetly, H.C., Wheeler, T.L. 2016. Effects of dietary protein concentration and ractopamine hydrochloride on performance and carcass characteristics of finishing beef steers. Journal of Animal Science. 94(5):2097-2102. doi:10.2527/jas2015-0225

Interpretive Summary: Ractopamine hydrochloride is used in the feedlot industry to increase daily gain, feed efficiency, and hot carcass weight with minimal negative effects on carcass quality. However, little work has been done to determine whether additional protein is needed in the diet to maximize the benefit of ractopamine hydrochloride in beef cattle. An experiment was conducted to determine the effects of high-concentrate finishing diets containing 13.5 and 17.5% crude protein with and without ractopamine hydrochloride for 30 to 33 d at the end of the finishing period. Beef steers were used in the experiment. Final body weight did not differ with feeding ractopamine hydrochloride; however, final body weight had a tendency to be 2% greater when the 13.5% crude protein diet was fed. Dry matter intake throughout the entire study was 12% greater for cattle fed the 13.5% crude protein than 17.5% crude protein diet. Gain-to-feed was 3.6% greater for cattle fed ractopamine hydrochloride vs. control and was 8.7% greater for cattle fed the 17.5% vs. the 13.5% crude protein diet. Hot carcass weight was not different for steers fed ractopamine hydrochloride or diets differing in protein. Dressing percentage was 1.5% greater for cattle fed ractopamine hydrochloride, but was not different between crude protein levels in the diet. Longissimus area, adjusted 12th rib fat, marbling score, and USDA yield grade did not differ across ractopamine hydrochloride or crude protein treatments. Our data indicate excess protein did not enhance the response to ractopamine hydrochloride. Furthermore, the improved performance from ractopamine hydrochloride reported by others was not observed except a small increase in feed efficiency.

Technical Abstract: Ractopamine hydrochloride (RAC) is used in the feedlot industry to increase daily gain, feed efficiency, and hot carcass weight with minimal negative effects on carcass quality. However, little work has been done to determine whether additional protein is needed in the diet to maximize the benefit of RAC in beef cattle. An experiment was conducted to determine the effects of high-concentrate finishing diets containing 13.5 and 17.5% CP with 0 or 300 mg of RAC for 30 to 33 d at the end of the finishing period. Beef steers were used in the experiment (n = 438; initial BW = 387.8 ± 1.9 kg). Cattle were randomly assigned to 1 of 4 treatments. Final BW did not differ (P = 0.37) with feeding RAC; however, final BW had a tendency to be 2% greater (P = 0.07) when the 13.5% CP diet was fed. No differences were noted for adjusted final BW for cattle fed 0 or 300 mg of RAC (P = 0.36) or cattle fed 13.5% or 17.5% diets (P = 0.93). Dry matter intake throughout the entire study was not different between steers fed 0 or 300 mg d-1 of RAC (P = 0.20), yet DMI was 12% greater for cattle fed the 13.5% CP than 17.5% CP diet (P < 0.01). Daily gain did not differ for cattle fed 0 vs. 300 mg d-1 RAC (P = 0.63); nor for cattle fed 13.5% CP vs. 17.5% CP (P = 0.16). Gain-to-feed was 3.6% greater for cattle fed 300 vs. 0 mg d-1 of RAC (P = 0.04). Gain-to-feed was 8.7% greater for cattle fed the 17.5% vs. the 13.5% CP diet (P < 0.01), which can be attributed to the decreased DMI for cattle fed the 17.5% CP diet. Hot carcass weight was not different for steers fed 0 or 300 mg d-1 of RAC (P = 0.36) or fed 13.5 vs. 17.5% CP (P = 0.93). Dressing percentage was 1.5% greater for cattle fed 300 vs. 0 mg d-1 of RAC (P = 0.05), but was not different between CP levels in the diet (P = 0.16). Longissimus area, adjusted 12th rib fat, and marbling score did not differ across RAC or CP treatments (P > 0.26). Additionally, no differences in USDA Yield Grade or percentage of cattle grading choice were detected for RAC or CP treatments (P > 0.26), which also supports the idea that at the same level of fatness before feeding RAC, it does not greatly impact 12th rib fat or intramuscular fat deposition. Our data indicate excess protein did not enhance the response to RAC and furthermore, the improved performance from RAC and furthermore, the improved performance from RAC reported by others was not observed other than a small increase in G:F.