Effects of feeding zilpaterol hydrochloride with and without monensin and tylosin on carcass cutability and meat palatability of beef steers

An experiment was conducted using 200 beef carcasses to evaluate the effects of feeding zilpaterol hydrochloride with or without monensin and tylosin on carcass cutability and meat sensory variables. The experiment was conducted using a randomized complete block design with treatments arranged as a 2 (no zilpaterol vs. zilpaterol) x 2 (monensin and tylosin withdrawn vs. monensin and tylosin fed) factorial. Cattle (n = 3,757) were fed zilpaterol hydrochloride, a beta(2)-adrenergic agonist, for 30 d at the end of the finishing period and withdrawn from zilpaterol hydrochloride for the last 5 d on feed. Five carcasses (weighing between 305 and 421 kg and free of slaughter defects) were selected from each of 40 feedlot treatment pens. Strip loins from the left sides were collected for sensory analysis and Warner-Bratzler shear force (WBSF) testing, and the rib was collected for 9th, 10th, 11th-rib dissections. A subsample of 3 carcass right sides per pen was fabricated into boneless subprimals according to Institutional Meat Purchase Specifications. Carcasses from zilpaterol-fed steers had greater (P <= 0.008) subprimal yields of shoulder clod, chuck tender, knuckle, top round, outside round, eye of the round, strip loin, top sirloin butt, bottom sirloin butt ball tip, full tenderloin, and flank steak than steers not fed zilpaterol. In addition, zilpaterol hydrochloride treatment decreased (P = 0.002) trimmable fat. Zilpaterol hydrochloride increased (P <= 0.006) estimated carcass protein and moisture and decreased (P <= 0.007) estimated carcass and LM fat percentage. For LM WBSF there was a zilpaterol hydrochloride x postmortem aging interaction (P < 0.01). The beta(2)-adrenergic agonist increased (P = 0.001) LM WBSF at 7, 14, and 21 d postmortem and decreased (P < 0.001) trained sensory-panel juiciness, tenderness, and flavor intensity of LM steaks aged for 14 d. A consumer sensory panel also found LM steaks from zilpaterol-fed steers were (P = 0.03) less tender than steaks from steers not fed zilpaterol; however, tenderness acceptability and overall acceptability were not affected (P >= 0.26). For the main effect of monensin and tylosin, withdrawal of monensin and tylosin decreased (P = 0.01) consumer juiciness scores, although other yield and compositional measurements were not affected (P >= 0.07). Zilpaterol is a strong repartitioning agent that increases meat yield through increased protein and decreased fat deposition.