IDENTIFY MECHANISMS BY WHICH OVULATORY FOLLICLE SIZE AFFECTS PREGNANCY ESTABLISHMENT AND MAINTENANCE IN BEEF COWS
Livestock and Range Research Laboratory (LARRL)
2013 Annual Report
1a.Objectives (from AD-416):
To improve our understanding of the mechanism(s) by which ovulatory follicle size affects pregnancy establishment and embryonic mortality.
1b.Approach (from AD-416):
ARS – A student from Conapec will visit the Fort Keogh Livestock and Range Research Laboratory (LARRL) and evaluate the effects of serum estradiol and ovulatory follicle size on embryo quality & morphology, and pregnancy establishment & maintenance in beef cows.
Conapec – members will evaluate effects of exogenous estradiol cypionate, equine chorionic gonadotropin, and temporary calf removal on ovulatory follicle size, and establishment / maintenance of pregnancy in large beef herds in Brazil. Information will be mutually shared between involved parties.
A student from Conapec Jr (an organization within UNESP, Botucatu, Sao Paulo, Brazil) worked at Fort Keogh Livestock and Range Research Laboratory (LARRL) and eventually completed a Master’s degree with Ohio State University. In her studies with Fort Keogh, we evaluated the effects of serum estradiol and ovulatory follicle size on embryo quality & morphology, and pregnancy establishment & maintenance in beef cows. Two manuscripts were published in the Journal of Animal Science from the results of this study. This research identified elevated serum concentrations of estradiol at the time of breeding as the most important variable affecting pregnancy success in beef cows. Greater concentrations of estradiol in the blood were highly correlated to ovulatory follicle size and subsequent progesterone production that is crucial to supporting pregnancy establishment. Supplementation of estradiol, to cows ovulating smaller follicles, improved pregnancy establishment and maintenance, but was not beneficial in cows ovulating larger follicles. Since beginning this cooperative agreement, it has become commonplace to give exogenous estradiol before artificial insemination for synchronizing ovulation in beef cows in Brazil. This outcome is the result of mutually shared results of intensive studies within this laboratory and field trials in Brazil that involved numerous members of the Conapec Jr organization.