Cyclic and pathologic changes of the mare endometrium as detected by biopsy, with a note on early embryonic death.

Normal histologic changes that occurred in concert with the ovarian cycle were evaluated. When combined with behavioral and physical findings, this evaluation enabled determination when there was synchrony between ovarian steroids (estrogen and progesterone) and their target tissues of endometrium. A system for classification as well as definitions of patterns types and degrees of severity of inflammatory and fibrotic changes was developed to facilitate a uniform system for description and communication. An attempt was made to relate the pathologic changes to their effect on fertility when fertility was defined as the ability to conceive, maintain, and deliver a live foal. This was done by dividing the types of endometrium into 3 categories, based on increasing degrees of extensiveness and severity of the various changes, and it was possible to show a high correlation of category to foaling rate. Embryonic and fetal loss from endometria with widespread periglandular fibrosis was observed. This was considered to be the major diagnosable cause of this type of reproductive failure.