Successful transfer of day 10 horse embryos: influence of donor-recipient asynchrony on embryo development.

The research article explores the effects of donor-recipient timing differences on the success of horse embryo transfers. The study concluded a broad window of time exists for successful pregnancy to be established in recipient mares via embryo transfer, despite timing differences, although these asynchronies may impact embryonic development.

Research Methodology

• The study involved the transfer of 78 horse embryos, ten days old, into recipient mares.
• These mares had ovulated either 9, 7, 6, 5, 4, 3, 2, or 1 day after the donor (negative asynchrony), on the same day(synchronous), or 2 or 4 days before the donor (positive asynchrony).
• Six to eight mares were observed under each group condition.

Observed Pregnancy Rates

• Successful pregnancy rates ranged between 63% to 100% in mares that ovulated 6 days after, to 2 days before, the donor.
• These varied rates indicate a broad window for successful pregnancy after the embryo transfer.

Effects on Embryo Survival

• The survival of embryos dipped when recipient mares ovulated seven days after the donor, and no embryos survived if recipients ovulated nine days after the donor.
• However, the embryo’s motion ceased and anchored at the uterine horn base when the conceptus was about 17 days old, regardless of the asynchrony degree.

Impacts on Embryo Growth and Development

• When the embryos were transferred into negatively asynchronous uteri, their growth and development were slowed down.
• When the greatest negative asynchrony degree was reached, where embryos survived to the heartbeat stage (i.e., -7 and -6 days), it was observed that the embryo and the allantois’ development was delayed.

Influence on Progesterone Priming

• Luteostasis was achieved in mares when the day 10 embryos were transferred under any asynchrony stage.
• The study suggests that the uterus’ progesterone priming to a stage equivalent to that of the transferred embryo isn’t required for the embryo’s survival.
• However, the progesterone stage does impact embryonic development.

Overall, while the synchronization between the donor and recipient does not entirely decide the success of the embryo transfer, its correlation with the developmental timeline of the embryo provides critical insights for maximizing successful outcomes in such procedures.