Preovulatory estradiol elicits an effect on pregnancy maintenance in beef cows

Authors: KETCHUM, JACLYN - Texas A&M University; PERRY, GEORGE - Texas A&M University; EPPERSON, KAITLIN - Texas A&M University; QUAIL, LACEY - Texas A&M University; OGG, MAKAYLA - Montana State University; Zezeski, Abby; RICH, JERICA J. - Arkansas State University; ZOCA, SAULO - South Dakota State University; KLINE, ADALAIDE - South Dakota State University; ANDREWS, TAYLOR - South Dakota State University; ORTEGA, M. SOFIA - University Of Missouri; SMITH, MICHAEL - University Of Missouri; Geary, Thomas

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Preovulatory estradiol concentrations and expression of estrus have been associated with greater pregnancy maintenance. This experiment was designed to determine if supplemental estradiol (E2) would improve pregnancy retention after embryo transfer. Cows were synchronized with the 7-d CO-Synch + CIDR® protocol. On d0 (48h post-prostaglandin), cows were grouped by estrual status (Estrual [Positive Control]; n=198, nonestrual; n=406). Nonestrual cows were administered GnRH and randomly assigned to either no treatment (Negative Control; n=204) or administration of 0.1 mg (IM) estradiol 17-'' (Estradiol; n=202). In a preliminary study, 0.1 mg (IM) estradiol 17-'' increased plasma estradiol (17.11±3.4 pg/mL; P<0.01) and remained elevated above baseline for approximately 8h compared to the control group (1.70±0.58 pg/mL). All cows received an in vivo produced frozen embryo on d7. Embryos were matched by grade, stage, and flush across treatments. Pregnancy status was retrospectively classified on d55/56/58 by transrectal ultrasonography, on d30 by plasma pregnancy-associated glycoproteins analysis (PAGs), on d24 by PAGs, expression of interferon-stimulated genes (ISGs), and plasma progesterone concentrations (P4), and on d19 by expression of ISGs and P4. Plasma estradiol (E2) concentrations (d-2, d0h0, d0h2) were analyzed by PROC MIXED as repeated measures in SAS (9.4), while GLIMMIX procedures were used to analyze differences in estrual status between d0 and d7 and pregnancy status with treatment, group, year, and their interactions as fixed effects. There was a treatment by time interaction (P<0.001) in E2 concentrations. There was no difference in plasma E2 concentrations on d0h0 (P>0.55) among treatments. At d0h2, Estradiol cows (15.7±0.25 pg/mL) had greater (P<0.001) plasma E2 compared to Positive Control (3.4±0.26 pg/mL) or Negative Control (4.3±0.25 pg/mL) cows, and Positive Control cows had lower plasma E2 than Negative Control cows (P=0.01). By d7, a greater (P<0.0001) proportion of cows in the Estradiol group (88%) expressed estrus compared to Negative Control cows (54%), indicating that the exogenous estradiol administered was sufficient to induce estrual activity in cows that were nonestrual at d0h0. All cows that received embryo transfer on d7 were considered pregnant, making the pregnancy rate on d7 for each treatment 100%. On d19, pregnancy rates did not differ (P=0.14) among treatment groups (Positive Control: 53%; Estradiol: 49%; Negative Control: 42%). On d24, Positive Control cows (47%) had greater (P<0.01) pregnancy rates than Negative Control (32%). Estradiol cows were intermediate (40%) to the Negative Control (P=0.16) and Positive Control (P=0.20) cows. There was no difference (P=0.38) in d30 pregnancy rates between Positive Control and Estradiol cows. At d30, Negative Control (27%) cows had lower (P=0.01) and tended (P=0.08) to have lower pregnancy rates than the Positive Control (41%) and Estradiol (36%) cows, respectively. However, pregnancy rates did not differ among treatment groups at d55 (Positive Control: 32%; Estradiol: 31%; Negative Control: 22%; P=0.12). Thus, preovulatory estradiol may be eliciting an effect on early uterine attachment or alter histotroph in a way that better prepares the conceptus to transition its nutritional source to choriovitelline thus improving pregnancy maintenance through day 30.