title: Effects of two beta-adrenergic agonists on finishing performance, carcass characteristics, and meat quality of feedlot steers.
abstract: The impact of using 2 beta-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 beta-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 beta-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 beta-agonists. The LM area was increased (P = 0.026) by ZH (75.2 cm(2)), but that of RH (72.2 cm(2)) was similar (P = 0.132) to the control steers (66.8 cm(2)). 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/cm(2)). Variables related to meat color indicated that both beta-agonists led to a similar redness of the LM area related to the control group. In general, feedlot performance was greatly enhanced by beta-adrenergic agonists, and meat tenderness from treated animals was classified as intermediate. Furthermore, meat color was not altered by beta-agonist supplementation.
authors.affiliation: Instituto de Ciencias Agrícolas, Universidad Autónoma de Baja California, Ejido Nuevo León, Baja California, México. lar62@uabc.mx
authors.forename: L
authors.initials: L
authors.lastname: Avendaño-Reyes
authors.forename: V
authors.initials: V
authors.lastname: Torres-Rodríguez
authors.forename: F J
authors.initials: FJ
authors.lastname: Meraz-Murillo
authors.forename: C
authors.initials: C
authors.lastname: Pérez-Linares
authors.forename: F
authors.initials: F
authors.lastname: Figueroa-Saavedra
authors.forename: P H
authors.initials: PH
authors.lastname: Robinson
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001823:Body Composition / Q000187:drug effects*; D001835:Body Weight / Q000187:drug effects*; D002417:Cattle / Q000254:growth & development*; D008297:Male; D008460:Meat / Q000592:standards*; D010627:Phenethylamines / Q000494:pharmacology*; D014297:Trimethylsilyl Compounds / Q000494:pharmacology*
chemical_list: D000318:Adrenergic beta-Agonists; D010627:Phenethylamines; D014297:Trimethylsilyl Compounds; C475840:Zilpaterol; C060897:ractopamine