Morpho-functional studies regarding the fertility prognosis of mares suffering from equine endometrosis

The aim of the present study was to characterize the morpho-functional features of endometrosis in barren and foaling mares, using both conventional histopathological and immunohistochemical methods. Endometrial biopsy samples were collected during the physiological breeding season from 159 estrous, clinically healthy mares (mean age 12 years), and the quality and degree of endometrosis was histomorphologically defined. The mares were bred and those that foaled were put in the foaling group whereas those that did not foal were placed in the barren group. Foaling mares were then compared with barren mares. Sixty-four percent (101/159) of uterine samples showed varying degrees of endometrosis and were used for this study. The sample population consisted of 51 barren and 50 foaling mares suffering from endometrosis. Expression of steroid hormone receptors (estrogen receptor, progesterone receptor) and endometrial protein secretion patterns (uteroglobin [UG], uterocalin [UC], calbindin(D9k) [CAL], uteroferrin [UF]) was evaluated by immunohistochemistry (barren mares N = 51, foaling mares N = 31). In comparison with unaffected glands, fibrotic glands generally showed a cycle-asynchronous, partially patchy protein expression pattern which is interpreted as a sign of endometrial maldifferentiation within fibrotic areas. In barren mares (N = 51) more than half of biopsy samples (27/51) showed a destructive mostly moderate (20/27) type of endometrosis. In affected glands, staining for UG (17/21) was decreased (P < 0.001). Foaling mares (N = 50) frequently showed a mild, nondestructive endometrosis (35/50). Compared with barren mares, foaling mares had statistically (P < 0.05) more often a cycle-synchronous or increased UG expression pattern within fibrotic glands. Obvious deviations of either UG or UC rarely occurred. Within fibrotic foci, UF often demonstrated a cycle-synchronous or more intense expression pattern in both foaling (28/31) and barren mares (41/51), compared with healthy glands. Mares of both groups showed a cycle-asynchronous staining for estrogen receptor and progesterone receptor in the stromal cells in areas of periglandular fibrosis and the glandular epithelia. These findings indicate that affected areas become independent of the uterine control mechanisms and exhibit specific differentiation dynamics. Immunohistochemical investigations showed that the secretory patterns differ between barren and foaling mares. The findings in this study should be considered as a useful addition to the "classical" Kenney categorization.