Abstract
A study was made of the growth performance of pasture-fed, 20-month-old Aberdeen Angus steers following implantation with either 30 mg or 45 mg hexoestrol in the autumn of 1959. The effects of reimplantation in the following spring, using the same dosages, were also studied. Hexoestrol implantation led to a marked increase in liveweight gain in the autumn, the 45 mg dosage producing the greatest rate of gain. Weight losses of treated steers slightly exceeded those of control animals during 88 days of sub-maintenance winter feeding. Growth rate in the spring was significantly increased only by implantation of the single, autumn dose of 45 mg hexoestrol. Re-implantation of 30 mg of the hormone did not augment the increased growth rate given by a single dose of 30 mg, while a double dose of 45 mg tended to depress liveweight gain as compared with the growth rate secured from a single dose of 45 mg. Over the complete trial of 232 days' duration, hormone treatment significantly increased liveweight ga...
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