Use of Progesterone and Estrogen in the Control of Reproductive Activities in Beef Cattle

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Abstract
Ten trials involving a total of 458 estrous cycles were conducted over a 4-year period to determine the ability of progesterone and estradiol benzoate to control the reproductive processes in beef cattle. Estrus and ovulation could be inhibited by daily injections of as little as 12.5 mg. progesterone. Estrus occurred 2.5 to 9.5 days post treatment in 86% (291/337) of the animals treated. Administration of 14 daily injections of progesterone had a depressing effect upon the rate of pregnancy in animals inseminated during estrus subsequent to treatment, with the higher dosages being more detrimental. An injection of 0.5−10.0 mg. of estradiol benzoate 3 days after the last injection of progesterone initiated estrus and caused ovulation without a further reduction in pregnancy rate. The estrogen also removed much of the variation in the onset of estrus, subsequent to progesterone administration, due to differences between groups of animals. There were no indications that any treatment affected productivity of the cow as measured by the weaning weight of calf suckling cow during the administration of the hormones, the gestation length, birth weight, or the sex ratio of calves born from inseminations during estrus subsequent to treatment. It is suggested that estrogen used in this sequence facilitates the release of the luteinizing hormone to cause ovulation in beef cattle. Copyright © . .