Evaluation of 0 or 300 mg of Optaflexx® on Growth Performance and Carcass Characteristics of Steers Fed to Different Degrees of Finish

A feedlot study evaluated the effects of ractopamine hydrochloride (Optaflexx®) dosage (0 or 300 mg/steer daily) and days on feed (118, 139, 160, 174 DOF) as a 2 × 3 + 1 factorial (steers fed 174 d were not fed Optaflexx) on performance of big yearlings. No interaction was observed between Optaflexx and days on feed. Feeding Optaflexx improved live final BW, carcass- adjusted ADG, carcass- adjusted feed conversion, and calculated yield grade. Increasing days on feed linearly increased live final BW, carcass-adjusted feed conversion, HCW, dressing percent, and marbling score but not ADG. Furthermore, a quadratic increase in LM area, 12th rib fat, and calculated yield grade was observed with days on feed. The response in added carcass weight due to feeding Optaflexx is the same with different lengths of time cattle are fed, and for large yearlings placed on feed