title: Impact of sorting before feeding zilpaterol hydrochloride on feedlot performance and carcass characteristics of yearling steers.
abstract: Two studies evaluated sorting and feeding zilpaterol hydrochloride (ZH) on feedlot performance and carcass characteristics in randomized block-designed finishing trials. In Exp. 1 (initial BW 342 ± 10 kg, = 1,000), 5 treatments included an unsorted non-ZH fed negative control (-CON), an unsorted ZH fed positive control (+CON), and 3 treatments in which the heaviest 20% within the pen were sorted and marketed 28 d early and the remaining 80% were fed ZH. The 20% were identified at the beginning (EARLY), 100 d from slaughter (MIDDLE), or 50 d from slaughter (LATE). Because of sorting, the remaining steers in sorted treatments were fed 14 d longer than -CON and +CON. Average days on feed for control treatments were 165 and 173 d for the EARLY, MIDDLE, and LATE treatments. In Exp. 2 (initial BW 376 ± 29 kg, = 1,400), 4 treatments included -CON; +CON; an early weight sort fed ZH (1-SORT) with the heaviest 20% identified at d 1 and sorted 50 d from harvest and marketed 14 d before -CON and +CON, with the remaining 80% of the pen fed 7 d longer than -CON and +CON; and a 4-way sort 50 d from harvest fed ZH (4-SORT) with steers sorted into HEAVY, MID-HEAVY, MID-LIGHT, and LIGHT groups marketed -14, 0, +7, and +28 d from -CON and +CON, respectively. Average days on feed for control treatments were 154 and 157 d for the 1-SORT and 159 d for 4-SORT. Steers were fed Zilmax at 8.3 mg/kg DM for 20 d followed by a 3 d withdrawal. In Exp. 1, steers fed +CON had 13 kg greater (P < 0.01) HCW than steers fed -CON. Steers sorted EARLY, MIDDLE, and LATE had 28, 25, and 24 kg heavier ( P< 0.01) HCW than -CON steers, respectively. Carcass weight SD was greater (P = 0.01) for +CON than -CON but was not different (P = 0.17) between -CON and ZH sorted treatments. Percentage of overweight carcasses (454 kg) was greater (P ≤ 0.05) in sorted treatments than in -CON. In Exp. 2, HCW for +CON was 15 kg heavier (P < 0.01) than that for -CON, and HCW for 4-SORT was greater (P < 0.02) than that for +CON. Carcass weight SD was not different (P > 0.10) between +CON and -CON, whereas carcass weight SD of 4-SORT was reduced (P < 0.01) compared with that of -CON and +CON. Steers fed ZH had a greater percentage of carcasses over 454 kg than steers fed -CON (P < 0.01). Although not statistically different (P = 0.27), the percentage of carcasses over 454 kg was reduced by 28% for 4-SORT compared with +CON. Feeding ZH increases carcass weight, but sorting reduces variation, allowing further increases in carcass weight while minimizing overweight carcasses.
authors.forename: F H
authors.initials: FH
authors.lastname: Hilscher
authors.forename: E M
authors.initials: EM
authors.lastname: Hussey
authors.forename: B L
authors.initials: BL
authors.lastname: Nuttelman
authors.forename: D B
authors.initials: DB
authors.lastname: Burken
authors.forename: W A
authors.initials: WA
authors.lastname: Griffin
authors.forename: K J
authors.initials: KJ
authors.lastname: Vander Pol
authors.forename: J P
authors.initials: JP
authors.lastname: Hutcheson
authors.forename: G E
authors.initials: GE
authors.lastname: Erickson
mesh_terms: D000367:Age Factors; D000821:Animal Feed; D000818:Animals; D001823:Body Composition / Q000187:drug effects* / Q000502:physiology; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D008297:Male; D016896:Treatment Outcome; D014297:Trimethylsilyl Compounds / Q000494:pharmacology*; D015430:Weight Gain / Q000187:drug effects / Q000502:physiology
chemical_list: D014297:Trimethylsilyl Compounds; C475840:Zilpaterol