Comparative effects of ractopamine hydrochloride and zilpaterol hydrochloride on growth performance, carcass traits, and longissimus tenderness of finishing steers

• Published in: Journal of animal science Vol. 88; no. 5; pp. 1823 - 1829
• Main Authors: SCRAMLIN, S. M, PLATTER, W. J, GOMEZ, R. A, CHOAT, W. T, MCKEITH, F. K, KILLEFER, J
• Format: Journal Article
• Language: English
• Published: Champaign, IL American Society of Animal Science 01.05.2010
• Subjects: Adrenergic beta-Agonists - pharmacology; Animal productions; Animals; Biological and medical sciences; Body Composition - drug effects; Cattle - growth & development; Food Additives - pharmacology; Food industries; Fundamental and applied biological sciences. Psychology; Male; Meat - standards; Meat and meat product industries; Muscle, Skeletal - drug effects; Phenethylamines - pharmacology; Terrestrial animal productions; Trimethylsilyl Compounds - pharmacology; Vertebrates; Ractopamine; Bovine; Growth; Meat product; Ox; Carcass; zilpaterol hydrochloride; Vertebrata; ractopamine hydrochloride; Meat animals; Mammalia; Tenderness; Artiodactyla; Beef; Performance; Ungulata
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2009-2405

Ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) are beta-adrenergic agonists that improve growth performance and affect carcass characteristics. The objective of this study was to evaluate the comparative effects of RAC and ZH when fed to beef steers during the last 33 d of the finishing period. Three hundred crossbred beef steers (516 +/- 8 kg) were grouped by BW, BCS, and breed type and randomly assigned to 1 of 3 treatments (10 steers per pen; 10 pens per treatment). Treatments were control (no beta-agonists added), RAC (200 mg of ractopaminexhdx(-1)d(-1), for 33 d), or ZH (75 mg of zilpaterolxanimalx(-1)d(-1), for 30 d, removed 3 d for required withdrawal period). Steers were slaughtered, carcass characteristics were evaluated, and cut-out yields were determined. Both RAC and ZH increased final BW, ADG, feed efficiency (G:F), and HCW compared with controls (P < 0.05). Compared with RAC, ZH decreased ADG, ADFI, and final BW, but increased HCW and dressing percentage (P < 0.05). Carcass yield was not affected by RAC in this experiment, whereas ZH decreased adjusted fat thickness and KPH, increased ribeye area, improved yield grade, and increased cut-out yields, when compared with controls (P < 0.05). Marbling, lean maturity, and skeletal maturity were not different between treatments (P > 0.05). Steaks from RAC steers had greater (P < 0.05) Warner-Bratzler shear force (WBSF) values than steaks from control steers at 3 and 7 d of aging, but did not differ from controls after 14 d of aging. Steaks from ZH steers had greater WBSF values (P < 0.05) than steaks from controls and RAC steaks throughout the 21-d postmortem aging period. Although both beta-adrenergic agonists were effective at improving feedlot performance, RAC showed no negative effect on WBSF after 14 d, whereas WBSF values for ZH steaks were significantly greater than controls after 21 d.