The effect of zeranol on growth rates of steers.

Abstract

Animal production in Australia THE EFFECT OF ZERANOL ON GROWTH RATES OF STEERS J.K.M. WELLINGTON* and H. GELDARD* Zeranol implants (Ralgro -Wellcome Australia Limited) are currently in use as growth promotants in over 30 countries. Their introduction in North America dates back to 1969 (Anon. 1979) but in Australia they have only recently become available. Experiments measuring increases in live weight of steers at pasture due to zeranol are reported here. Trial herds were located at Braidwood, Goulbum, Khancoban, Nariel and Tallangatta. In each herd cattle were weighed after fasting for 15 hours, and randomly allocated to treatment or control groups. Treatment groups received three 12 mg zeranol pellets subcutaneously at the base of the ear. The groups were run together and weighed again at the conclusion of the experiment. TABLE 1 Summary of weight gains of steers Despite wide variation among the herds in climatic and nutritional conditions, age, initial weight, and rate of gain of control groups, treatment resulted in similar increases in liveweight gains. Provided steers have sufficient pasture available to support weight gains of 0.6 to 1.2 kg per day, implantation with 36 mg zeranol should increase rate of gain by 12-32%. Further experiments using female cattle not intended for breeding are in progress. ANON. (1979). Vet. Med. Small Anim. Clin. 74: == 584. * Wellcome Australia Limited, 53 Phillips Street, Concord, N.S.W. 2137. 484