Earlier this year, FDA approved the use of a beta-agonist, ractopamine, as a growth promotant during the last 28 to 42 days of the finishing period for feedlot steers and heifers. It is marketed by Elanco Animal Health under the trade name of Optaflexx™. It is recommended to be fed at the rate of 200 mg/head/day for 28 days. A five-trial summary of steers showed the following improvements over controls: Live wt. gain, +17.3 lb; dressing percent, +0.3%; hot carcass wt., 14.1 lb, ribeye area, +0.4 sq. in.; yield grade score, -0.1. Because there was no change in dry matter intake, a significant improvement in feed efficiency was observed. There were no differences in marbling score or quality grade.

At the recent Southwest Nutrition and Management Conference, Dr. Aubrey Schroeder presented the results of a study on shear force and sensory evaluation of strip loin steaks. When Optaflexx™was fed at the recommended level of 200 mg/head/day, there were no changes from controls in Warner-Bratzler shear force or sensory evaluation of tenderness, juiciness and flavor. However, when fed at 300 mg/head/day, there was a significant change in shear force and sensory tenderness.

In summary, when fed at the 200 mg level, there are significant improvements in gain, feed efficiency, and carcass muscling along with no reductions in marbling or tenderness (Schroeder, A. 2004. Southwest Nutrition and Management Conference, Phoenix, AZ, Feb. 26-27).