title: Effect of zilpaterol hydrochloride duration of feeding on performance and carcass characteristics of feedlot cattle.
abstract: Four trials, each with a randomized complete block design, were conducted with 8,647 beef steers (initial BW = 346 +/- 29.6 kg) in 3 different locations in the United States to evaluate the effects of zilpaterol hydrochloride (ZH) on performance and carcass characteristics of feedlot cattle. Treatments consisted of feeding ZH (8.33 mg/kg of dietary DM) for 0, 20, 30, or 40 d, at the end of the feeding period, followed by a 3-d withdrawal period before slaughter. Cattle were weighed on d 0 and 50 before slaughter (in 3 of the 4 studies), and on the day of slaughter. Data from the 4 trials were pooled for statistical analyses. No differences (P > or = 0.78) were detected among treatments for ADG and G:F from the start of the study until the final 50 d on feed. Final BW was greater for the average of the 3 ZH-treated groups (P < 0.01) than for the 0-d group. Average daily gain was greater for ZH-treated vs. control cattle during the final 50 d on feed (P < 0.01) and for the entire feeding period (P < 0.01). No differences in DMI were noted for any periods of the experiment (P > or = 0.42) for ZH-treated cattle vs. controls. No differences were noted for DMI among the ZH-treated groups for the final 50 d on feed (P = 0.81) or for the overall feeding period (P = 0.31). Feeding ZH for any length of time increased G:F (P < 0.01) for the final 50 d and overall compared with 0-d cattle. In addition, a linear increase with more days of ZH feeding was observed for G:F during the period that ZH was fed (P = 0.01), as well as for the overall feeding period (P = 0.01). The ZH-treated cattle had heavier HCW (P < 0.01), greater dressing percent (P < 0.01), reduced marbling scores (P < 0.01), less 12th-rib fat (P < 0.01), larger LM area (P < 0.01), less KPH (P = 0.01), and a lower USDA yield grade (P < 0.01) than the 0-d cattle, regardless of the duration of ZH feeding. Dressing percent increased linearly (P < 0.01) with increased duration of ZH feeding, whereas 12th-rib fat (P = 0.07), marbling scores (P < 0.01), and USDA calculated yield grade (P = 0.01) decreased linearly with increased duration of ZH feeding. Feeding ZH increased ADG and G:F and decreased overall carcass fatness. In addition, effects of ZH on measures of carcass fatness were enhanced by feeding the product for a greater length of time.
authors.affiliation: Clayton Livestock Research Center, New Mexico State University, Clayton 88415, USA.
authors.forename: N A
authors.initials: NA
authors.lastname: Elam
authors.forename: J T
authors.initials: JT
authors.lastname: Vasconcelos
authors.forename: G
authors.initials: G
authors.lastname: Hilton
authors.forename: D L
authors.initials: DL
authors.lastname: VanOverbeke
authors.forename: T E
authors.initials: TE
authors.lastname: Lawrence
authors.forename: T H
authors.initials: TH
authors.lastname: Montgomery
authors.forename: W T
authors.initials: WT
authors.lastname: Nichols
authors.forename: M N
authors.initials: MN
authors.lastname: Streeter
authors.forename: J P
authors.initials: JP
authors.lastname: Hutcheson
authors.forename: D A
authors.initials: DA
authors.lastname: Yates
authors.forename: M L
authors.initials: ML
authors.lastname: Galyean
mesh_terms: D018663:Adrenergic Agents / Q000008:administration & dosage / Q000494:pharmacology; D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001823:Body Composition / Q000187:drug effects*; D002417:Cattle; 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