Effects of estradiol cypionate (ECP) on ovarian follicular dynamics, synchrony of ovulation, and fertility in CIDR-based, fixed-time AI programs in beef heifers

Estradiol cypionate (ECP) was used in beef heifers receiving a controlled internal drug release (CIDR; insertion=Day 0) device for fixed-time AI (FTAI) in four experiments. In Experiment 1, heifers ( n=24) received 1 mg ECP or 1 mg ECP plus 50 mg commercial progesterone (CP) preparation i.m. on Day 0. Eight or 9 days later, CIDR were removed, PGF was administered and heifers were allocated to receive 0.5 mg ECP i.m. concurrently (ECP0) or 24 h later (ECP24). There was no effect of treatment ( P=0.6) on mean (±S.E.M.) day of follicular wave emergence (3.9±0.4 days). Interval from CIDR removal to ovulation was affected ( P