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What is embryo transfer? Why would you consider performing embryo transfer on your mare? How is embryo transfer accomplished?

You have always wanted your mare to have a foal, but she is too busy in the show ring to take time off for “maternity leave”. Embryo transfer can make it possible for your mare to have a foal, without missing the entire show season due to pregnancy. Simply put, embryo transfer is having a fertilized egg (embryo) harvested from one mare (the donor), and implanting it into another mare (the recipient) for the remainder of the gestation period. The recipient mare is, in human terms, a surrogate mother to the baby. Embryo transfer is often performed for mares that are actively being shown and unable to take time off to have their own foal. It is also useful for mares that are physically or reproductively unable to carry a foal to term.

When the donor mare is in heat (in season), she is bred just as she would be if she were to carry the foal herself. A reproductive ultrasound is done a day or two later, to be sure that she has ovulated. About 7 or 8 days after ovulation, we use a special fluid to flush the fertilized egg (embryo) out of the mare’s uterus—this is also known as “harvesting” the embryo. The embryo is extremely small at this stage—invisible to the naked eye. A special filter is used to catch the embryo as it is flushed from the mare’s uterus. A microscope is used to identify and grade the embryo. Special handling skills are needed to transfer the embryo into holding media, where it can stay 24 hours under ideal conditions.

The embryo is then carefully placed into a recipient mare where it will live until full term. This recipient mare will be the surrogate mother; she will carry the foal until birth and continue to be the foal’s mother until weaned. Although the foal is carried by the surrogate mother, it will have the genetics of the donor mare and stallion. If you are interested in learning more about embryo transfer for your mare, please contact Fox Valley Equine Practice.