Histology of reproduction in harp and grey seals during pregnancy, postparturition, and estrus

Abstract

Reproductive tracts were collected on the eastern coast of Canada from adult female grey seals (Halichoerus grypus) during gestation and postparturition, and from adult female harp seals (Phoca groenlandica) during delayed implantation and postparturition. Reproductive tracts were fixed in 10% buffered formalin for light microscopy. The placental site and adjacent tissue were preserved in 2% glutaraldehyde – 1% paraformaldehyde for scanning electron microscopy. During the delay of blastocyst implantation, the endometria of the gravid and nongravid uterine horns were similar in microscopic appearance. During gestation, maternal septa were often surrounded by maternal epithelium deep into the placental labyrinth except distally, where the maternal cells were replaced by syncytium. Marginal hematomas increased in size and complexity throughout placentation. Following parturition, uterine regression occurred earlier in harp seals (10 days postpartum) than in grey seals (21–25 days postpartum). Postpartum changes were most pronounced in the placental site where the blood vessels underwent extensive reorganization. In some specimens, the extensively vascularized placental site of the previous pregnancy was still apparent 12 months later. Epithelial replacement in the uterus was complete in grey seals 21–25 days postpartum and sooner in harp seals. Cervical and vaginal stratification occurred in both phocids following parturition and increased towards estrus. A recently ovulated grey seal was obtained between 21 and 25 days postpartum. The vaginal stratification and the presence of sperm in their uterine horns indicated that grey seals began estrus about 12–17 days postpartum. In harp seals, estrus appeared to occur towards the end of the lactational period, about 10–12 days postpartum.