Fig. 1.

Experimental design. The estrous cycles of crossbred beef heifers were synchronized using a 7-day progesterone (P4)-releasing intravaginal device (CIDR; 1.38 g of P4) with administration of a prostaglandin F2α analog (PG) the day before CIDR removal. A) Experiment 1. Heifers (n = 19) were allocated to one of two groups: cyclic (nonbred) or pregnant (artificially inseminated at standing estrus). All heifers were slaughtered on Day 3 after estrus. B) Experiment 2. To ensure the ovulation, 0.02 mg of a GnRH agonist (buserelin) was administered 32 h after CIDR removal. Heifers (n = 17) were allocated to one of two groups: cyclic, sham transfer in both oviducts or pregnant with 50 in vitro-produced presumptive zygotes transferred in the ipsilateral oviduct and a sham transfer carried out in the contralateral oviduct. All transfers were carried out endoscopically on Day 1.5, and all animals were slaughtered on Day 3 after estrus. ET, endoscopic transfer.