Effect of Optaflexx ® 45 (Ractopamine-HCl) on Live and Carcass Performance when Fed to Steers During the Final 28 Days of Feeding

The goal of this study was to evaluate the effects of Optaflexx supplementation to steers during the final 28 d of feeding on live and carcass performance. Thirty-four steers were separated into four harvest groups and fed at the University of Florida Beef Teaching Unit. Within each harvest group, the steers were separated into two pens. Both pens were fed a control diet of 85% corn, 7.5% cottonseed hulls, and 7.5% commercially produced protein pellet. When pens were visually 28 d from reaching a pen average of 0.4 inch of backfat, pens were supplemented with a top dress that contained 0 and 200 mg•hd•dof Optaflexx. After d 28 of supplementation for each harvest group, steers were transported to the University of Florida Meats Laboratory and harvested under Federal inspection. A University employee collected carcass data 48 h postmortem. 72 h postmortem, the strip loin and top round were removed from the right side of each carcass. The Semimembranosus, Adductor, and Gracilis were separated from the top round and the Longissimus dorsi was separated from the strip loin. Commodity weight, denuded weight, and muscle dimensions were collected on all muscles of interest. Whole denuded muscles were then vacuum packaged, wet aged until d 13 postmortem, and cut into 1 inch steaks for tenderness evaluation by Warner-Bratzler shear force. The inclusion of Optaflexx during the final 28 d of feeding did not have an effect (P > 0.05) on live performance characteristics. In addition, most carcass characteristics were unaffected (P > 0.05) by supplementation except dressing percentage (P < 0.20), lean maturity (P < 0.05), marbling score (P < 0.05), and muscle firmness (P < 0.20). The muscle weights and dimensions of the adductor and semimembranosus were unaffected (P > 0.05) by Optaflexx supplementation. Only the width and minimum depth of the longissimus dorsi and gracilis were improved by Optaflexx. Finally, tenderness of steaks from all four muscles as evaluated by Warner-Bratzler shear force was unaffected by Optaflexx.