Control of ovarian function for assisted reproductive technologies in cattle

Although the discovery that follicles in bovine ovaries grow in a wave-like fashion has presented challenges for estrus synchronization and superovulation, recent protocols, designed to control follicular function have permitted fixed-time AI or fixed-time embryo transfer with high pregnancy rates, and the initiation of superstimulatory treatments at a self-appointed time, all without the necessity of estrus detection. The key is the synchronization of follicle wave emergence. More recent studies have revealed that it is not only possible to synchronize the timing of ovulation for fixed-time AI in single ovulating animals, but also in superstimulated donors. Ultrasound-guided follicle ablation is very efficacious in synchronizing follicle wave emergence but is difficult to apply in the field. Similarly, the induction of ovulation with GnRH or LH will effectively synchronize follicle wave emergence, but ovulation occurs in only 60 to 70% of cases. The administration of estradiol benzoate in progestin-treated cattle effectively synchronizes follicle wave emergence for both superovulation and estrus synchronization, but estradiol benzoate is not available in many countries. The challenge now is to use knowledge of follicle wave dynamics to design alternatives.