INFLUENCE OF CHRONIC DEGENERATIVE ENDOMETRITIS (ENDOMETROSIS) ON PLACENTAL DEVELOPMENT IN THE MARE

Placentation between 80 and 220 days of gestation was studied by measu rement of fetal dimensions and gross, light and transmission and scann ing electron microscopic examinations of the allantochorion and endome trium from 4 fertile mares with no, or very mild, endometrial histopat hology and 6 subfertile Thoroughbred mares suffering varying degrees o f age-related chronic degenerative endometritis (endometrosis). Sponta neously occurring twin gestation was observed in 3 animals. Several of the subfertile mares and endometrial cysts which showed 2 distinct fe atures during pregnancy: those located near the lumenal surface of the endometrium showed no sign of microcotyledon development in both the endometrium and the opposed, flat and smooth allantochorion, whereas e ndometrial cysts located deeper in the stroma were covered by apparent ly normal glands and microcotyledons. Fetal dimensions were lower in t he subfertile mares, but still within the reference range. Microcotyle don development appeared to be delayed and the chorionic macro- and mi crovilli looked shorter and blunter between 80 and 120 days in the 2 s ubfertile mares compared to the fertile mares at the same gestational ages. At 120 days, the subfertile mare had significantly less microvil li per surface area than her fertile counterpart and her fetus weighed only half that from her counterpart, despite a similar crown-rump len gth. However, between 150 and 220 days the difference in microcotyledo n development between the young fertile and old subfertile mares was m uch less marked, despite the continued existence of considerable numbe rs of distended 'gland nests' in the endometrium of the latter group.