Reproductive Endocrinology and Hormonal Control of the Estrous Cycle

Abstract

Maximizing reproductive efficiency depends upon whether a heifer attains puberty before the start of the breeding season, conceives early in the breeding season, calves unassisted, raises the calf to the time it is marketed, and the heifer/cow must conceive to calve early during the subsequent calving seasons. Failure to do so constitutes reproductive loss, which is estimated to cost the US beef industry around $500 million annually. Estrous synchronization and artificial insemination are among the most powerful and applicable technologies for genetic improvement of beef herds. Development of new and improved methods of synchronizing estrus and ovulation depends on an understanding of the physiological and hormonal mechanisms controlling the estrous cycle and the initiation of estrous cyclicity in noncycling heifers and postpartum cows. It is imperative for veterinarians and producers to familiarize themselves with commercially available estrous synchronization products and the physiologic mechanisms by which these products synchronize estrus and (or) ovulation in cattle.