Histological changes in the uterus during postpartum in the mare.

An histological study of the postpartum period in 29 mares was carried out. Uterine biopsies were taken daily during the first 10 days postpartum in a total of 87 samples. At day 0, equine endometrium was characterized in the surface by the presence of regularly ordered microcaruncles; the stratum spongiosum was oedematous and contained distended and scarce glands. Degenerative changes in microcaruncles and endometrial glands were present on day 1 postpartum. The epithelium of the microcaruncles from 2 to 5 days postpartum showed cytoplasmic vacuolization, karyorrhexis and an inflammatory reaction with neutrophils and phagocitic cells. On day 7 postpartum, the histology of the endometrium was similar to the normal proestrus with cuboidal luminal epithelium and an oedematous stromal tissue. The changes are usually completed within days 9 and 10 postpartum with the histologically typical appearance of estrus in mares.