199 Expanding use of fixed-time artificial insemination in beef heifers and cows through improved strategies to manage estrus and ovulation

摘要

Breeding strategies that facilitate fixed-time artificial insemination (FTAI) in beef heifers and cows rely on improved methods to control estrus and ovulation by manipulating follicular waves and luteal lifespan. Procedures that facilitate synchronization of estrus in estrous cycling females and induction of an ovulatory estrus in pre- or peri-pubertal heifers and anestrous postpartum cows increase reproductive rates and expedite genetic progress. Progestins, including melengestrol acetate (MGA®) and Controlled Internal Drug Release (CIDR®), have been used effectively to synchronize estrus in beef heifers when used strategically with GnRH and PGF2α. Long-term progestin-based protocols are used extensively in beef heifers and provide an advantage over short-term protocols resulting from pre-synchronization with a progestin prior to the administration of PGF2α and GnRH. The 5- or 7-day CO-Synch + CIDR® protocols are used effectively in beef cows, and perhaps perform more predictably in cows than in heifers because of an improved response to GnRH. Although protocols currently recommended to synchronize estrus and ovulation prior to FTAI are effective, continued research efforts are needed to develop strategies that maximize the proportion of females expressing estrus and minimize the number of females for which ovulation must be induced. These efforts may include development of alternative breeding strategies such as split-time artificial insemination (STAI), in which insemination of non-estrous females is delayed to allow for increased estrus expression and the potential for better alignment of ovulation with insemination. Estrous response and pregnancy rates were improved in beef heifers and cows using a STAI approach. Further improvements in pregnancy rates to FTAI may be realized through development of synchronization programs that improve control of ovarian follicular development and enhance synchrony of estrus expression. Collectively, advancements in applied reproductive technologies over the past two decades afford beef producers the flexibility to match specific breeding management protocols to a defined management system and create the opportunity to expand use of AI in beef herds across the United States.