title: Effect of extended withdrawal of zilpaterol hydrochloride on performance and carcass traits in finishing beef steers.
abstract: The objective was to evaluate the effects of an extended withdrawal period after feeding the beta-adrenergic agonist zilpaterol hydrochloride (ZH) for 20 d at the end of the feeding period. Three hundred eighty-four crossbred beef steers were blocked by BW and randomly allocated into 64 pens (6 steers/pen). Pens were assigned to treatments in a 2 x 4 factorial arrangement in a randomized complete block design. Main effects were the addition of 0 (control) or 8.3 mg/kg of ZH (DM basis) to the finishing diet for 20 d before estimated average slaughter date and paired withdrawal periods of 3, 10, 17, or 24 d before slaughter. Individual BW were measured initially, 1 d before ZH feeding, and 1 d before slaughter. The ZH feeding period was initiated so that control cattle in the 3-d withdrawal group would be expected to average 65% USDA Choice Quality grade and have 1.27 cm of 12th-rib fat based on visual appraisal. Carcass data were collected at slaughter. For the 3-d withdrawal steers, 2 steers from each pen were selected to determine visceral organ and total offal mass at slaughter. The ZH x withdrawal day interaction was not significant (P > 0.10) for the majority of variables. There was no difference (P > or = 0.12) due to ZH feeding for final BW, carcass-adjusted final BW, or ADG. However, DMI was decreased (P = 0.02) and G:F increased (P = 0.01) in steers fed ZH vs. control steers. As day after withdrawal of ZH increased, there was a linear increase (P < 0.001) in final BW and carcass-adjusted final BW, but a linear decrease (P < 0.001) in ADG over the finishing period and over the ZH plus withdrawal period. Overall, HCW was 380 and 369 kg (P < 0.001) for ZH and control steers, respectively. However, the difference between ZH and control was 14, 17, 5, and 6 kg with 3, 10, 17, and 24 d withdrawal, respectively (ZH x withdrawal day, P = 0.09). Feeding ZH increased dressing percentage (65.8 vs. 64.6%; P < 0.001) and LM area (94.8 vs. 89.7 cm(2); P < 0.001), and decreased calculated yield grade (2.69 vs. 2.91; P = 0.03) and percentage of cattle grading USDA Choice (31.1 vs. 42.3%; P = 0.03) compared with controls. Small intestinal mass (g/kg of empty BW) was greater (P = 0.03) for steers fed ZH compared with controls. There were no other differences (P > or = 0.11) in mass of body components, expressed in kilograms or as a fraction of empty BW. In this experiment, improvements in animal performance and HCW due to feeding ZH were generally maintained when withdrawal was extended through 10 d.
authors.affiliation: Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.
authors.forename: B P
authors.initials: BP
authors.lastname: Holland
authors.forename: C R
authors.initials: CR
authors.lastname: Krehbiel
authors.forename: G G
authors.initials: GG
authors.lastname: Hilton
authors.forename: M N
authors.initials: MN
authors.lastname: Streeter
authors.forename: D L
authors.initials: DL
authors.lastname: Vanoverbeke
authors.forename: J N
authors.initials: JN
authors.lastname: Shook
authors.forename: D L
authors.initials: DL
authors.lastname: Step
authors.forename: L O
authors.initials: LO
authors.lastname: Burciaga-Robles
authors.forename: D R
authors.initials: DR
authors.lastname: Stein
authors.forename: D A
authors.initials: DA
authors.lastname: Yates
authors.forename: J P
authors.initials: JP
authors.lastname: Hutcheson
authors.forename: W T
authors.initials: WT
authors.lastname: Nichols
authors.forename: J L
authors.initials: JL
authors.lastname: Montgomery
mesh_terms: D018663:Adrenergic Agents / Q000008:administration & dosage* / Q000494:pharmacology*; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000254:growth & development*; D004032:Diet / Q000662:veterinary; D004334:Drug Administration Schedule; D008297:Male; D014297:Trimethylsilyl Compounds / Q000008:administration & dosage* / Q000494:pharmacology*; D015430:Weight Gain / Q000187:drug effects
chemical_list: D018663:Adrenergic Agents; D014297:Trimethylsilyl Compounds; C475840:Zilpaterol