title: Effects of zilpaterol hydrochloride on growth rates, feed conversion, and carcass traits in calf-fed Holstein steers.
abstract: Two experiments were conducted to evaluate the effectiveness of zilpaterol hydrochloride (ZH) to enhance growth performance and carcass characteristics in calf-fed Holstein steers. In Exp. 1, Holstein steers (n = 2,311) were fed in a large-pen trial in 2 phases at a commercial feed yard in the desert Southwest. In Exp. 2, a total of 359 steers were fed in a small-pen university study. In Exp. 1 and 2, cattle were implanted with a combination trenbolone acetate-estradiol implant approximately 120 d before slaughter. Cattle were fed ZH for 0, 20, 30, or 40 d before slaughter at a rate of 8.3 mg/kg (DM basis). A 3-d withdrawal was maintained immediately before slaughter. Cattle within an experiment were fed to a common number of days on feed. During the last 120 d before slaughter, ADG was not enhanced by feeding ZH for 20 d (P = 0.33 in Exp. 1, and P = 0.79 in Exp. 2). Gain-to-feed conversion was increased by feeding ZH for all durations in Exp. 1 (P < 0.05). Feeding ZH increased HCW by 9.3 (Exp. 2) to 11.6 (Exp. 1) kg at 20 d compared with the control groups. Across both experiments, dressing percent was increased for all durations of feeding ZH (P < 0.05). Although skeletal maturity score, liver integrity, lean color, fat thickness, and KPH were not affected by feeding ZH for 20 d in either experiment (P >or= 0.6), LM area was increased for all durations of feeding ZH (P < 0.05). The percentage of carcasses identified as USDA Choice was reduced (P < 0.01) for all durations of feeding ZH in Exp. 1. This effect was not observed in Exp. 2. Holstein steers clearly respond to the beta-agonist ZH, and 20 d of feeding ZH with a 3-d withdrawal significantly increased carcass weights, muscling, and carcass leanness.
authors.affiliation: Beckett Consulting Services, Atascadero, CA 93422, USA. jbeckett@beefconsulting.com
authors.forename: J L
authors.initials: JL
authors.lastname: Beckett
authors.forename: R J
authors.initials: RJ
authors.lastname: Delmore
authors.forename: G C
authors.initials: GC
authors.lastname: Duff
authors.forename: D A
authors.initials: DA
authors.lastname: Yates
authors.forename: D M
authors.initials: DM
authors.lastname: Allen
authors.forename: T E
authors.initials: TE
authors.lastname: Lawrence
authors.forename: N
authors.initials: N
authors.lastname: Elam
mesh_terms: D000821:Animal Feed; D000822:Animal Husbandry; D000818:Animals; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D004032:Diet / Q000662:veterinary; D005503:Food Additives / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology*; D008297:Male; D008460:Meat / Q000592:standards; D009753:Nutritive Value; D014297:Trimethylsilyl Compounds / Q000494:pharmacology*; D015430:Weight Gain / Q000187:drug effects
chemical_list: D005503:Food Additives; D006133:Growth Substances; D014297:Trimethylsilyl Compounds; C475840:Zilpaterol