Impact of elevated preovulatory estradiol during a fixed-time AI protocol on uterine environment and embryonic survival to day 16

Abstract Text: The role of preovulatory estradiol in maternal recognition of pregnancy and embryonic survival has not been well established among beef cows. Our objective was to determine the effects of preovulatory estradiol on regulating the uterine environment from fertilization to maternal recognition of pregnancy. Beef cows/heifers were synchronized with the CO-Synch protocol and AIed (d 0). Blood was collected to determine estradiol (d -2 to 0) and progesterone (d 0 to 16) concentrations. Cows were classified by expression of estrus (estrus and no estrus). Uteri were flushed to collect d16 embryos nonsurgically (Rep 1; n = 29), or following slaughter (Rep 2; n = 37). Flush media was analyzed for protein and glucose concentrations. Data were analyzed using the mixed procedure in SAS.  There was an effect of estrus, time, and estrus by time (P < 0.01) on circulating concentrations of estradiol, with cows in estrus having greater concentrations of estradiol.  There was no effect of estrus (P = 0.41) or estrus by time (P = 0.16) on subsequent circulating concentrations of progesterone.  There was no difference in embryo recovery rate between estrus and no estrus animals (P = 0.20; 48% vs 29%) and between replicates (P = 0.46; 44% vs 33%). There were no differences between estrus and no estrus animals for uterine flush protein (P = 0.36; 2222 ± 513 vs 1547 ± 525 mg/mL). However, cows that showed estrus had greater glucose concentrations in uterine flush media (P = 0.05; 51 ± 1.86 vs 45 ± 1.92 mg/dL). Cows in which an embryo was recovered had greater concentrations of protein in the uterine flush (P = 0.05; 2643 ± 585 mg/mL) compared to cows in which an embryo was not recovered (1126 ± 463 mg/mL). There were no differences in uterine flush glucose between cows that did or did not have an embryo recovered (P = 0.29; 47 ± 2.12 vs 50 ± 1.70 mg/dL). In summary, embryo recovery rates and uterine flush protein content did not differ between cows that did or did not exhibit estrus, but uterine flush glucose content was greater in cows that exhibited estrus.  There was no difference in uterine flush glucose content between cows that did and did not have an embryo but uterine flush protein content was greater in cows from which an embryo was recovered.  USDA is an equal opportunity provider and employer.

Keywords: Estradiol, embryonic survival, uterine environment