Controlling the dominant follicle in beef cattle to improve estrous synchronization and early embryonic development

Abstract

Estrous synchronization and timed ovulation programs that permit AI at a predetermined time (timed AI) rather than as determined by detection of spontaneous estrus are requisite for increased adoption of AI in the beef cattle industry. In the past two decades, significant progress has been achieved in developing programs that synchronize ovulation to address this need. While this progress has been driven by a multitude of fundamental discoveries in reproductive biology, the greatest impact in the past two decades has been the result of enhanced understanding of the pattern of ovarian follicle growth in cattle and development of technologies to coordinate growth and ovulation of the dominant follicle. At present, estrous synchronization programs that result in acceptable timed AI pregnancy rates are available for beef cattle. The capacity to control growth of the dominant follicle and evaluate the impact of various approaches on fertility has resulted in greater understanding of the factors that influence maturity of ovulatory follicles. Modifications to the standard industry breeding programs, with the aim of lengthening and/or increasing the gonadotropic stimulus and estradiol production by preovulatory follicles, have been shown to substantially increase timed AI pregnancy rate in beef cattle. Associations between characteristics of follicular development and fertility have surfaced from application of estrous and ovulation synchronization technologies and led to investigation of the fundamental mechanisms that underlie these relationships.