Abnormal cell proliferations in in vivo equine embryos – Implications for a successful pregnancy

Summary Recovery of early equine embryos from the uterus provides an opportunity to assess their morphology microscopically and detect any abnormalities, which may have implications for pregnancy establishment and loss thereafter. During recovery of equine embryos, for either research purposes or commercial embryo transfer, abnormal proliferations of cells were noted in the blastocoele and/or attached to the cells on the periphery of the blastocoele of 7 expanded blastocysts. To the authors' knowledge, these anomalies have not previously been reported in the literature. Therefore, the aim of this article is to describe these abnormalities and report if such morphological changes are compatible with embryo survival. Three of the embryos were transferred to recipient mares, and all resulted in a pregnancy. Two of the pregnancies resulted in the birth of a normal foal and the third, in a research mare, developed normally before it was terminated at Day 32 of pregnancy. Hence, these cellular proliferations in the 3 embryos which were transferred to a recipient mare did not appear to influence conceptus development and survival. We hypothesise that the morphological anomalies seen in the 7 blastocysts reported here result from overproliferation of trophectoderm or primitive endoderm.