Effects of two β-adrenergic agonists on finishing performance, carcass characteristics, and meat quality of feedlot steers.

The impact of using 2 p-adrenergic agonists in feedlot cattle fed finishing diets was evaluated using 54 steers (45 crossbred Charolais and 9 Brangus) initially weighing 424 + 26.6 kg in a randomized complete block design with 3 treatments and 6 blocks (i.e., 18 pens with 3 steers per pen). Response variables were feedlot performance, carcass characteristics, and meat quality. Treatments were 1) control (no supplement added); 2) zilpaterol hydrochloride (ZH; 60 mg·steer^-1·d^-1); and 3) ractopamine hydrochloride (RH; 300 mg·steer^-1·d^-1). The β-agonists were added to the diets during the final 33 d of the experiment. The groups of steers fed ZH or RH improved (P < 0.01) ADG by 26 or 24%, respectively, compared with control steers. Steers supplemented with RH consumed less (P = 0.03) DM (8.37 kg) than control steers (8.51 kg), whereas intake was similar (P = 0.37) for ZH and control steers. Addition of either p-agonist to the diet considerably improved (P < 0.01) the G:F (ZH, 0.253 and RH, 0.248 vs. control, 0.185). Hot carcass weight and carcass yield were enhanced (P < 0.05) with both β-agonists. The LM area was increased (P = 0.026) by ZH (75.2 cm²), but that of RH (72.2 cm²) was similar (P = 0.132) to the control steers (66.8 cm²). Meat from the ZH- (P = 0.0007) and RH- (P = 0.0267) supplemented steers had greater shear force values than control steers (ZH = 5.11; RH = 4.83; control = 4.39 kg/cm²). Variables related to meat color indicated that both p-agonists led to a similar redness of the LM area related to the control group. In general, feedlot performance was greatly enhanced by p-adrenergic agonists, and meat tenderness from treated animals was classified as intermediate. Furthermore, meat color was not altered by β-agonist supplementation. [ABSTRACT FROM AUTHOR]