2010 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. 3.Progress Report Collection and transfer of embryos from cows that ovulated either large or small follicles into cows that ovulated different sized follicles was completed and suggested a disconnect in the role that ovulatory follicle size has on fertilization, early embryonic health, pregnancy establishment and pregnancy maintenance. More specifically, ovulation of a larger follicle resulted in greater fertilization success and improved embryo viability and growth, as well as serum progesterone concentration by day 7 after breeding, but had a negative effect on establishment of pregnancy. We interpret this to mean that the oocyte from a larger follicle is more fertile, but the increased number of granulosa cells in the larger follicle produces a progesterone profile after ovulation that may shorten the time frame for the embryo to produce sufficient signal (interferon-tau) to establish a pregnancy. Manuscripts detailing these results are in preparation. ADODR monitoring is via emails and phone calls.