Dominant follicle blood flow at the onset of proestrus does not affect steroid hormones, endometrial receptors, or follicular perfusion in beef cows under FTAI treatment regimens.

Gonadotropins exert angiogenic and steroidogenic effects in the ovary. Likewise, recombinant equine chorionic gonadotropin (reCG) and GnRH through FSH and LH actions, may affect follicular perfusion, steroidogenesis, and the uterine milieu. The aim of the study was to determine dominant follicle irrigation at the onset of proestrus and to evaluate the associated effects on follicular perfusion, steroidogenic activity, and endometrial receptors abundance, following reCG and GnRH administration in beef cows subjected to estradiol (E2)/progesterone (P4)-based fixed-time artificial insemination (FTAI) treatment regimen. At P4 device removal, dominant follicles were classified as "Irrigated" or "Non-Irrigated" and randomly assigned to a 2 × 4 factorial design to be administered reCG, GnRH, reCG + GnRH, or no additional treatment. Follicular irrigation, follicular diameter, and plasma E2 and P4 concentrations during proestrus were assessed by Doppler ultrasonography and electrochemiluminescence. Follicular fluid E2 and P4, and endometrial abundance of estrogen (ESR1, ESR2) and progesterone (PR) receptors at final proestrus were evaluated using electrochemiluminescence and immunohistochemistry. Repeated-measures variables were analyzed using GLMM, and endpoint variables using one-way ANOVA. In females treated with GnRH, there was increase in follicular diameter compared with those of the irrigated control group on day 9 (P < 0.05), whereas in females treated with reCG and reCG + GnRH there were no differences (P > 0.05). Neither blood perfusion status nor treatments modified follicular irrigation, plasma P4 and E2 concentrations, follicular fluid E2 concentrations, or endometrial receptor abundance in females of any group (P > 0.05). In conclusion, dominant follicle blood flow at proestrus onset does not predict subsequent ovarian or uterine responses.