Effects of duration of zilpaterol hydrochloride feeding and days on the finishing diet on feedlot cattle performance and carcass traits

• Published in: Journal of animal science 2008-08, Vol.86 (8), p.2005-2015
• Main Authors: Vasconcelos, J.T, Rathmann, R.J, Reuter, R.R, Leibovich, J, McMeniman, J.P, Hales, K.E, Covey, T.L, Miller, M.F, Nichols, W.T, Galyean, M.L
• Format: Article
• Language: English
• Subjects: Adrenergic Agents - administration & dosage; Adrenergic Agents - pharmacology; Animal Feed - analysis; Animal Nutritional Physiological Phenomena; Animal productions; Animals; backfat; beef cattle; beta-adrenergic agonists; Biological and medical sciences; body weight; carcass characteristics; carcass yield; Cattle - growth & development; days on feed; Diet - veterinary; dressing percentage; Drug Administration Schedule; dry matter intake; equations; feed conversion; feed rations; feedlots; finishing; Food industries; Fundamental and applied biological sciences. Psychology; liveweight gain; mathematical models; Meat and meat product industries; meat grades; medicated feeds; steers; Terrestrial animal productions; Trimethylsilyl Compounds - administration & dosage; Trimethylsilyl Compounds - pharmacology; Vertebrates; Weight Gain - drug effects
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2008-1032

British and British x Continental steers (n = 560; initial BW = 339.4 ± 1.76 kg) were used in a serial slaughter study with a completely random design to evaluate effects of zilpaterol hydrochloride (ZH; 8.33 mg/kg of dietary DM basis) on performance and carcass characteristics. Treatments were arranged in a 4 x 4 factorial (112 pens; 7 pens/treatment; 5 steers/pen) and included duration of ZH feeding (0, 20, 30, or 40 d before slaughter plus a 3-d ZH withdrawal period) and days on feed (DOF) before slaughter (136, 157, 177, and 198 d). No duration of ZH feeding x slaughter group interactions were detected for the performance measurements (P > 0.10). Final BW did not differ (P = 0.15) between the 0-d group and the average of the 3 ZH groups, but ADG was greater for the average of the 3 ZH groups during the period in which ZH diets were fed (P < 0.01) and for the overall feeding period (P = 0.05). As duration of ZH feeding increased, DMI decreased (P = 0.01) and G:F increased linearly (P < 0.01). With the exception of KPH (P = 0.022), no duration of ZH feeding x slaughter group interactions (P > 0.10) were detected for carcass characteristics. Regardless of the duration of ZH feeding, cattle fed ZH had greater HCW (P < 0.01), greater dressing percent (P < 0.01), less 12th-rib fat (P < 0.01), larger LM area (P < 0.01), less KPH (P = 0.03), and lower yield grade (P < 0.01) than the 0-d cattle. The 0-d group had greater marbling scores (P < 0.01) than cattle fed ZH diets, with a tendency for a linear decrease in marbling score (P = 0.10) as duration of ZH feeding was extended. A greater percentage of carcasses in the 0-d group graded USDA Choice or greater (P < 0.01) than in the 3 ZH groups, whereas the percentage of Select carcasses was greater (P = 0.01) for the 3 ZH groups. From d 0 to end (P = 0.04) and during the last 43 d on feed (P < 0.01), ADG responded quadratically to DOF before slaughter. No differences were detected among slaughter groups for DMI for the entire trial period; however, a quadratic response (P = 0.02) was observed for the final 43 d before slaughter. A quadratic response was also detected for the final 43 d before slaughter (P < 0.01) and from d 0 to end (P = 0.02) for G:F. Final BW, HCW, dressing percent, and 12th-rib fat increased linearly (P < 0.01) as DOF before slaughter increased. Our results indicate that no substantial effects on performance and carcass measurements were observed when ZH was fed for 30 or 40 d as opposed to 20