Proliferation and Apoptosis in Fetal Membranes and Endometrium During Placental Retention in Heavy Draft Mares

Placental retention (retained placenta [RP]) is a serious and common peripartum disease in mares, but the etiology and pathogenesis of RP still remain unclear. The alteration of cell proliferation and apoptosis is considered to be an important factor in RP. Fetal membranes and endometrial biopsies were collected from mares with RP (n = 8) and from control mares (n = 10). The proliferation and apoptosis levels in the chorionic and the endometrial epithelia were assessed by proliferating cell nuclear antigen immunostaining and the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay, respectively. The study revealed that there was an insignificant decrease in proliferation and a significant increase in apoptosis in the chorionic epithelium from mares with RP. This result excludes a proliferation imbalance from the possible causes of RP. In the area of the nonpregnant horn of the placenta, proliferation was negatively correlated and apoptosis was positively correlated with the degree of fetomaternal anchorage. It was observed that, in all mares with placental retention, the endometrial epithelium (both luminal and glandular) showed decreased proliferation and increased apoptosis, which may indicate a delay in postpartum uterine regeneration.