Uterine vascular degeneration is present throughout the uterine wall of multiparous mares. Colinearity between elastosis, endometrial grade, age and parity.

Vascular degeneration is present in endometrial vessels of multiparous aged mares. The lesions associated with vascular degeneration consist of enlargement, duplication and splitting of the membrana elastica interna and perivascular deposits of elastin. However, there are no similar data available for deep myometrial vessels and the vascular layer. The objectives of the present study were to characterize the status of vasculature in full-thickness uterine necropsy samples and to correlate these findings to endometrial grade, age, and parity. Elastosis was present in myometrial vessels, as well as in large arteries and veins located between the circular and longitudinal myometrial layers. Vascular degeneration was associated with number of foals (P < 0.001) and endometrial grade (P < 0.05), but not with mare age (P > 0.05). Endometrial grade was associated with age (P < 0.001) and vascular grade (P < 0.05), but not with number of foals (P > 0.05). The presence of elastosis in the myometrial vessels was related to problems associated with chronic uterine infection (CUI) and delayed uterine clearance (DUC) of infertile mares. Uterine contractility was impaired in mares affected by CUI and/or DUC and could be related to a lack of myometrial blood flow. Additionally, degeneration of large vessels in the vascular layer may indicate a general compromise in uterine blood flow and fertility. The main conclusions were the presence of vascular elastosis in large deep myometrial vessels as well as in endometrial vessels, and that the factor with the strongest association with vascular degeneration was number of foals (P < 0.001), followed by endometrial grade (P < 0.05), but no association with mare age.