Functional disturbances in the endometrium of barren mares: a histological and immunohistological study

Different types of endometrial maldifferentiation were investigated by histopathological (haematoxylin-eosin (HE), periodic acid Schiff-alcian blue and picro-sirius red staining) and immunohistological (oestrogen and progesterone receptors, Ki-67 antigen, intermediate filaments and laminin) analysis of endometrial biopsy specimens from mares (n=34), most of which had been barren for at least 1 year. Two major features were observed: (i) unequal differentiation, in which two functional stages are visible within a single biopsy sample: areas which are differentiated in accordance with the stage of the ovarian cycle and multiple glandular nonfibrotic foci deviating from the dominant physiological pattern; and (ii) irregular endometrial differentiation, in which there are diffuse abnormalities of functional glandular morphology that cannot be appointed to any physiological endometrial stage. The basic diagnosis was made in HE-stained slides. Special stains and immunohistological analysis confirmed endometrial maldifferentiation concerning at least one, but mostly all, of the parameters investigated. Endometrial maldifferentiation was not related to the age or parity of mares, or to the annual season. The aetiopathogenesis and prognosis of endometrial maldifferentiation are not known. However, the findings of the present study indicate that endometrial maldifferentiation should be included in the routine assessment of endometrial biopsy specimens.