Effect of ractopamine–HCl supplementation for 28 days on carcass characteristics,muscle fiber morphometrics,and whole muscle yields of six distinct muscles of the loin and round

This study evaluated the effects of ractopamine–HCl (RAC) supplementation on carcass characteristics, muscle fiber morphometrics, and tenderness. Thirty-four steers (2 groups, 4 replicates) were fed RAC or carrier for 28 days prior to harvest. Seventy-two hours postmortem, the Longissimus lumborum (LL), Gracilis (GRA), Vastus lateralis (VL), Rectus femoris (RF), Semimembranosus (SM), and Adductor (ADD) were dissected from each carcass. Commodity weight, denuded weight, and muscle dimensions were collected. RAC supplementation tended to affect dressing percentage (P = 0.15) and muscle firmness (P < 0.15), and significantly affected lean maturity (P < 0.05) and marbling score (P < 0.05). With the exception of the LL and GRA (P < 0.05), RAC had no effect on muscle dimensions. RAC did not influence the tenderness of vacuum-packaged, aged steaks as measured by Warner–Bratzler shear force. Muscle fiber size within the six muscles was unchanged (P > 0.05) by RAC. Thus, RAC improves carcass parameters without a negative impact on tenderness.