Influence of chronic degenerative endometritis (endometrosis) on placental development in the mare.

The research investigated the impact of a chronic degenerative condition (endometrosis) in the uterus on placental development in horses. The study, which involved measuring fetal dimensions as well as examining the endometrium and allantochorion, revealed some differences in development and growth in subfertile mares compared to fertile mares.

Study Participants and Methods

• Researchers studied placentation during 80 to 220 days of gestation in horses.
• The study involved four fertile mares with minimal endometrial histopathology and six subfertile Thoroughbred mares with varying degrees of endometrosis, an age-related chronic endometritis.
• Fetal dimensions were measured and gross, light and transmission, and scanning electron microscopic examinations were conducted on the allantochorion and endometrium.
• Three of the subjects were observed to have spontaneously occurring twin gestation.

Findings on Endometrial Cysts and Microcotyledon Development

• Several subfertile mares had endometrial cysts with two distinct features noticed during pregnancy.
• Cysts located near the endometrium’s lumenal surface displayed no sign of microcotyledon development, resulting in both the endometrium and the allantochorion being flat and smooth.
• Conversely, endometrial cysts located deep in the stroma were covered by normal glands and microcotyledons.

Observations on Fetal Dimensions

• Fetal dimensions in subfertile mares were lower compared to fertile mares, although still within the reference range.
• Microcotyledon development seemed delayed in subfertile mares, and the chorionic macro- and microvilli appeared shorter and blunter within 80 and 120 days of gestation.

Comparisons between Fertilie and Subfertile Mares

• At 120 days of gestation, a subfertile mare exhibited significantly fewer microvilli per surface area compared to her fertile counterpart, and her fetus weighed only half that of the fetus of the fertile mare — despite having a similar crown-rump length.
• However, between 160 and 220 days of gestation, the difference in microcotyledon development between the young fertile and old subfertile mares was less pronounced, even though the latter group continued to have a considerable number of distended ‘gland nests’ in the endometrium.

Conclusion

• The study demonstrated that endometrosis can affect placental development in horses, leading to differences in fetal growth and development.
• These findings could help provide better reproductive care and management for subfertile mares affected by endometrosis.