Effects of zilpaterol hydrochloride and zilpaterol hydrochloride withdrawal time on beef carcass cutability, composition, and tenderness.

The impact of zilpaterol hydrochloride (ZH) on carcass yield, composition, and tenderness was evaluated using 384 beef steers in a randomized complete block design. Main effects were the addition of 0 or 8.3 mg/kg of ZH for the final 20 d of feeding and each inclusion level was paired with withdrawal periods of 3, 10, 17, or 24 d. The 2 animals with BW closest to the pen average were selected for carcass fabrication to determine carcass yield, composition, and tenderness. The carcasses from animals fed ZH had greater (P = 0.008) individual side weights. Carcass fat determinations were unchanged (P = 0.70) by ZH. Weights of the strip loin (P = 0.01), peeled tenderloin (P = 0.02), and top sirloin butt (P < 0.001) were all improved with ZH. When expressed as a proportion of carcass weight, ZH increased percentage of carcass in the top sirloin butt (P = 0.006), bottom sirloin tri-tip (P = 0.02), top inside round (P = 0.002), bottom round flat (P = 0.001), and flank steak (P = 0.02). A longer withdrawal time (WT) increased (P < 0.001) carcass weights. Shoulder clod weights were greatest (P < 0.001) with 17-d WT from ZH, whereas chuck roll weights were greatest (P = 0.02) at 17 and 24 d of WT. Peeled tenderloins, top sirloin butts, and eye of rounds responded to WT, with increased (P < 0.001) weights seen at 10 d of WT as compared with all other WT. Shear force values were greater at each of the 3 aging times, 7 d (P < 0.001), 14 d (P < 0.001), and 21 d (P = 0.003), in steaks from ZH-fed steers compared with control steers. Protein percentages were greater in ZH steaks (P = 0.03) and ZH ground beef trim (P < 0.001). Percent moisture was increased (P < 0.001) in strip loin steaks at 3 and 10 d WT. Ground beef trim had an increase (P = 0.04) in percent moisture and a decrease (P = 0.01) in percent fat at 10 d WT. Carcass weights and yields were improved with ZH feeding and may continue to improve even up to 10 d after withdrawal of the supplement. Tenderness was slightly reduced with ZH supplementation but was unaffected by WT. Zilpaterol hydrochloride can be a valuable supplement to finishing beef steers to improve carcass lean yields and composition.