Control of Ovarian Function for Fixed-timed AI and Embryo Transfer without Estrus Detection G.A. Bó 1* and R.J. Mapletoft 2 1 Instituto de Reproducción Animal Córdoba (IRAC), Córdoba, Argentina 2 Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK Canada Introduction Elective abbreviation or prolongation of the luteal phase can result in estrus and ovulation within a range of 4 days, which obviates fixed-time AI (FTAI), but is generally acceptable for embryo transfer recipients. The variation in the interval to estrus and ovulation has been attributed to variations in follicular wave status at the time of treatment. Recent protocols designed to control both luteal and follicular status provide new possibilities for synchronization that is precise enough to permit FTAI or transfer of embryos without the need for estrus detection (FTET). Synchronization of estrus and ovulation Prostaglandin F2α (PGF) has been most commonly used for synchronization of estrus in cattle (1). Early studies showed that PGF did not effectively induce luteolysis during the first 5 d following estrus, and when luteolysis was induced, the ensuing estrus occurred over a 6-day period. The interval from PGF treatment to estrus and ovulation is determined by the stage of development of the dominant follicle at the time of treatment. These responses emphasize that both luteal and follicular phases must be controlled to precisely control the timing of ovulation. There are several possible ways to control follicular development in cattle. Although follicle ablation is easily mastered, it requires more sophisticated equipment and skill than a hormone injection and consequently, it has been used mainly in superstimulation protocols (1); hormone treatments are commonly used in estrus synchronization protocols. GnRH and pLH An injection of GnRH or pLH can induce ovulation of a dominant follicle (10), which will result in synchronous emergence of a new follicular wave, on average, 2 d later. Therefore, protocols that utilize GnRH and PGF have been developed for fixed-time AI in beef and dairy cattle. The protocol known as Ovsynch (13), involves an injection of GnRH followed in 7 d by PGF, an injection of GnRH 48 h later, and FTAI in 0-24 h; Cosynch involves AI at the second GnRH. The Ovsynch protocol has been less efficacious in heifers than in cows primarily because the first injection of GnRH induces ovulation in only about 50% of heifers and more than 80% of cows (11,13). The addition of a CIDR to a 7-day GnRH-based protocol improved pregnancy rates after FTAI in heifers (11), and improved pregnancy rates in non-cycling, lactating dairy cows (15), but not in cycling beef (11) or dairy (15) cows. Published in IVIS with the permission of the WBC Close window to return to IVIS www.ivis.org Proceedings of the WBC Congress, Québec, Canada , 2004