Separation of the placenta in the ewe: an ultrastructural study.

Placental separation in the ewe appears to involve an explosive degeneration of the chorionic epithelium which occurs in the short space of time between parturition and the delivery of the fetal membranes. In the goat there is a similar mechanism of separation. By contrast separation of the placenta in the cow appears to depend upon a detachment at the junctional region between fetal and maternal epithelia. There is no obvious explanation for these findings. The results are discussed in the light of the placental hormonal environment in the period which immediately precedes parturition.