Control of estrus and ovulation in beef heifers and cows

Abstract

Until recently, labor required to detect estrus for individual cows or heifers in a herd was the primary reason beef producers viewed artificial insemination as impractical. However, improvements in methods to control estrus and ovulation in beef heifers and cows are now expanding the use of artificial insemination by reducing the time required to detect estrus or eliminating estrus detection entirely. These methods evolved as a result of expanded understanding of the bovine estrous cycle and improved ability to effectively manipulate both follicular waves and luteal lifespan. Modern protocols are now capable of facilitating fixed time artificial insemination in beef cattle through orchestrated use of progestins, gonadotropin releasing hormone, and prostaglandin. These strategies offer effective control of estrus and ovulation in estrous cycling females and are also capable of inducing an ovulatory estrus in high percentages of peripubertal heifers and anestrous postpartum cows. Additionally, alternative breeding management strategies have been developed to achieve higher fertility while still reducing labor associated with estrus detection, such as combined estrus detection and fixed time artificial insemination approaches, or more recent approaches such as split time artificial insemination. Advancements in applied reproductive technologies now afford beef producers flexibility in matching specific breeding management protocols to defined management systems. This review focuses on systems currently recommended to facilitate fixed time artificial insemination among beef heifers and cows in the United States, where these technologies offer beef producers a clear opportunity to simultaneously improve genetic merit and reproductive management of their herds.