Role of preovulatory estradiol in uterine and luteal function
Abstract
In beef heifers, expression of estrus at fixed-time artificial insemination (FTAI) was associated with increased preovulatory circulating concentrations of estradiol (E2) and increased pregnancy rates compared to heifers that were not detected in estrus (Richardson et al., 2016). We hypothesized that increased preovulatory concentrations of estradiol would enhance conceptus elongation in beef heifers. To test the preceding hypothesis conceptus elongation on day 16 (day 0 = GnRH-induced ovulation) was examined in Angus heifers having low (5.0 [plus or minus] 0.6; pg/mL n=6) or high (10.2 [plus or minus] 1.0 pg/mL; n=6) preovulatory concentrations of E2 on day 0 (P< 0.0005). In vivo produced embryos (n=5 per heifer) were transferred on day 7, and reproductive tracts were recovered and flushed on day 16 of gestation. Mean ([plus or minus] SEM) conceptus number and length did not differ (P > 0.15) between heifers in the Low E2 (2.5 [plus or minus] 0.7; 7.1 [plus or minus] 1.7 cm) and High E2 (2.3 [plus or minus] 0.5; 5.2 [plus or minus] 1.3 cm) groups, respectively. Consequently, circulating concentrations of preovulatory E2 did not affect pre-implantation conceptus elongation. Therefore, a second experiment was conducted to examine embryonic loss in heifers exposed to low (3.7 [plus or minus] 0.3 pg/mL; n=19) or high (7.0 [plus or minus] 0.4 pg/mL; n=25) preovulatory concentrations of estradiol on day 0 (GnRH-induced ovulation) between days 7 (embryo transfer) and 36 spanning a critical period for implantation. Pregnancy was monitored using circulating progesterone concentrations (days 16 to 24), pregnancy associated glycoproteins (days 22 to 36), and ultrasonography (days 30 and 36). Pregnancy rate did not differ between the Low and High E2 groups on days 22, 24, 30, or 36. A potential explanation for why there was no difference in pregnancy rate between the Low and High E2 groups, is that preovulatory estradiol in the Low E2 group was not as low as in other studies in which a difference in pregnancy rate was detected.
Degree
M.S.
Thesis Department
Rights
OpenAccess.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License.