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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 gain, with an outstanding increase resulting from the single dose of 45 mg hexoestrol.
Dressing-out percentage was reduced by the single dose of 45 mg hexoestrol, but not by other dosage levels.
Hexoestrol implantation led to a significant increase in carcass weight, estimated at approximately 29 lb, with little evidence of real differences between the dosage levels in the average response to the hormone.
The internal “bone” temperature of the hot carcass was higher in steers implanted with 45 mg hexoestrol than in other steers, but lower after 24 hours of chilling.