The effects of embryo-uterine asynchrony on early embryonic development

Abstract

Equine pregnancy has an extraordinary ability to tolerate embryo-uterine asynchrony. Indeed, while ruminant embryos will not survive negative asynchrony (i.e. the recipient ovulated after the donor) of more than 2 days [Lawson RAS,et.al, J Reprod Fertil, 1975;45:101-7], horse embryos will continue to develop in the uterus of a recipient that ovulated up to 7 days later [Wilsher S,et.al, Reproduction 2010;139:575-85.]. However, negative asynchrony of more than 4 days appears to compromise embryo development and survival and may therefore be a useful model to study embryo-maternal communication. This study examined the effects of negative uterine asynchrony on the development of equine embryos over a period of either 6 or 11 days. Embryos were recovered on day 8 after ovulation and transferred non-surgically to synchronous (day 8; donor-recipient difference 1⁄4 0 days) or asynchronous (day 3; donor-recipient difference 1⁄4 -5 days) recipient mares. The resulting conceptuses were recovered either 6 days later by uterine lavage or 11 days later using a video-endoscopically-guided net (n 1⁄4 5 per group in all cases). Prior to recovery, vesicle size was determined ultrasonographically; following recovery the embryonic disc and, for conceptuses recovered on day 11 post-ET, the embryo proper were identified, measured and staged in terms of primitive steak formation and indices of embryo development such as crown-rump length and somite