Presence of embryos increases uterine blood flow and affects endometrial gene expression in Holstein cows on day seven post-insemination.

Superovulation treatment leads to characteristic changes in uterine perfusion during the first three weeks of pregnancy in cattle, but the origin of these changes is unknown. We investigated embryo-induced effects on uterine blood flow volume (uBFV) and pulsatility index (uPI), as well as on steroid hormone concentrations during the first seven days after conception, together with endometrial gene expression at the time of embryo flushing, in Holstein Friesian cows. Animals (n = 8) underwent (a) artificial insemination (AI), (b) superovulation followed by artificial insemination (SOV-AI), and (c) superovulation followed by sham AI (SOV-control) in a Latin square design. Doppler ultrasound examinations and blood collections were performed 12 h before AI, as well as on days 1, 3, 5, and 7 post AI. Embryo flushing followed by endometrial biopsy collection was also performed on day 7 post AI. While uBFV was higher after SOV-AI compared to AI on days -0.5, 3, 5 and 7 post AI (P < 0.05), uPI was not affected (P > 0.05). Progesterone and total estrogen concentrations were increased following superovulation at all timepoints (P < 0.05) but were not affected by the presence of embryos (P > 0.05). Compared to AI treatment, SOV-AI was associated with increased KDR and decreased NOS3 endometrial mRNA expression (both P < 0.05) on day 7 post AI. Taken together, our results demonstrate changes in uterine blood flow during the first seven days after AI, and in endometrial gene expression in response to the presence of embryos at this time.