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This article in JAS

  1. Vol. 87 No. 12, p. 4092-4100
    Received: Jan 16, 2009
    Accepted: Aug 25, 2009
    Published: December 5, 2014

    1 Corresponding author(s):


Effects of zilpaterol hydrochloride on growth rates, feed conversion, and carcass traits in calf-fed Holstein steers

  1. J. L. Beckett 1,
  2. R. J. Delmore,
  3. G. C. Duff,
  4. D. A. Yates§,
  5. D. M. Allen§,
  6. T. E. Lawrence# and
  7. N. Elam
  1. Beckett Consulting Services, Atascadero, CA 93422;
    Department of Animal Science, California Polytechnic State University, San Luis Obispo 93422;
    Department of Animal Sciences, The University of Arizona, Tucson 85721;
    Intervet/Schering Plough Animal Health, Millsboro, DE 19966;
    Beef Carcass Research Center, West Texas A&M University, Canyon 79016; and
    Clayton Livestock Research Center, New Mexico State University, Clayton 88415



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 ≥ 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 β-agonist ZH, and 20 d of feeding ZH with a 3-d withdrawal significantly increased carcass weights, muscling, and carcass leanness.

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