Uterine Vascular Perfusion and Involution During the Postpartum Period in Mares

In horses, limited data is found regarding the vascular events during uterine involution at the puerperal period. Thus, we aimed to evaluate the morphological aspects (size of uterus and intrauterine fluid content) and the hemodynamics (endometrial and mesometrial vascular perfusion) of the uterus during its postpartum involution process. Ten mares were daily scanned by transrectal color Doppler ultrasonography from the first day postpartum (d1) to the 16th day after first postpartum ovulation (D0 = ovulation). The formerly gravid horn (GH) and formerly nongravid horn (NH) were individually evaluated. A reduction (P < .05) in the uterine diameter was observed during the first 7 days postpartum, and the rate of uterine involution decreased after this period. The involution was completed on d21 and d24 for the NH and GH, respectively. Presence of intrauterine fluid was present in large amounts between d1 and d2 postpartum, followed by a decrease (P < .05) between d4 and d7. No fluid was observed after d16 postpartum or after the third day postovulation (D3). During the early postpartum period, an increase (P < .05) in the endometrial and mesometrial vascularization was detected, respectively, between d1 and d4, and between d1 and d2. The vascular perfusion did not differ after d4 for endometrial tissue, whereas was reduced (P < .05) between d2 and d10 for mesometrium. After the first postpartum ovulation, an increase (P < .05) in vascular perfusion was observed from D0 to D5, followed by a decrease (P < .05) between D5 and D11 and an increase (P < .05) between D11 and D14. The novel vascular perfusion profile here described in the endometrium and mesometrium after ovulation is similar to the uterine vascular profile observed during estrous cycles and early pregnancy, indicating a fast return of the mare's uterus to cycling postpartum conditions.