Real-time characterization of the uterine blood flow in mares before and after artificial insemination

The present experiment was divided into two studies to investigate the effect of age and endometrial degeneration on uterine blood flow of mares throughout the immediate post-breeding period. In study 1, uterine blood flow was characterized in mares (n = 7 mares/group) with minimal, moderate or severe endometrial degenerative changes (GI, GII and GIII, respectively). In study 2, the effect of age was investigated using young (≤ 6 years) and old (≥ 15 years) mares (n = 7 mares/group). Uterine vascular perfusion and mesometrial pulsatility index (PI) were evaluated every hour from H0 (moment immediately before AI) to H12. In study 1, a pronounced and transitory increase on uterine vascular perfusion was detected (P < 0.001) between H1 and H3 in the three endometrial groups. In addition, GIII mares had greater (P < 0.05) mesometrial PI than GI mares during the post-breeding period, denoting reduced uterine blood flow. In study 2, a transitory increase on uterine vascular perfusion was also observed in both age groups during the first hour after mating. However, mesometrial PI of young and old mares was similar (P > 0.05) and constant (P > 0.7) through the first 12h after AI. Results demonstrated, for the first time, the immediate changes on uterine vascular perfusion and mesometrial PI in response to semen infusion. Moreover, reduced blood flow of the uterus during the post-breeding period was strongly associated with endometrial degenerative changes in mares, regardless of age.