Influence of preovulatory estradiol treatment on the maintenance of pregnancy in beef cattle receiving in vivo produced embryos.

This experiment was designed to determine the role of preovulatory estradiol in pregnancy retention after embryo transfer (ET). Cows were synchronized with the 7-d CO-Synch + CIDR® protocol. On d0 (d-2 =CIDR® removal), cows were grouped by estrual status (estrual [Positive Control] and nonestrual), and nonestrual cows were administered Gonadotropin Releasing Hormone (GnRH) and randomly assigned to either no treatment (Negative Control) or Estradiol (0.1 mg estradiol 17-β IM). All cows received an embryo on d7. Pregnancy status was retrospectively classified on d56, 30, 24, and 19 by either ultrasonography, plasma pregnancy-associated glycoproteins analysis (PAGs), expression of interferon-stimulated genes, plasma progesterone (P4) concentrations, or a combination of the factors. There was no difference in estradiol concentrations on day 0 h 0 (P > 0.16). At day 0 h 2, Estradiol cows (15.7 ± 0.25 pg/mL) had elevated (P < 0.001) estradiol compared with Positive Controls (3.4 ± 0.26 pg/mL) or Negative Controls (4.3 ± 0.25 pg/mL). On d19, pregnancy rates did not differ (P = 0.14) among treatments. On d24, Positive Controls (47%) had greater (P < 0.01) pregnancy rates than Negative Controls (32%); Estradiol cows were intermediate (40%). There was no difference (P = 0.38) in pregnancy rates between Positive Control (41%) and Estradiol (36%) cows on d30, but Negative Control (27%) cows had (P = 0.01) or tended (P = 0.08) to have decreased pregnancy rates, respectively. Thus, preovulatory estradiol may elicit an effect on early uterine attachment or alter histotroph components, consequently improving pregnancy maintenance through d30.