Sixty-four beef cattle, in each of 2 years, were treated in a factorial design with hormonal implants, in-feed antibiotic and supplementary dietary undegradable protein in order to measure complementary influences of the three treatments on growth, feed intake and carcass characteristics. In the case of heifers the in-feed antibiotic preparation avoparcin was of considerable benefit to growth, and this was not further enhanced by the use of Zeranol implantation or dietary fishmeal. Hormonal implantation alone was of some benefit. Response to fishmeal was variable. In the case of steers avoparcin was again beneficial to growth and this benefit was enhanced by both Zeranol/Trenbolone acetate but not by fishmeal. The very positive response of steers to Zeranol/Trenbolone acetate was further enhanced by both avoparcin and by supplementary dietary fishmeal. Hormonal implantation resulted in larger, leaner carcasses with marginally reduced eating quality. © 1991.
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