Why do Embryo Transfer?

The technique of passing an embryo from one mare (donor) into another (recipient) has become a viable service for so many reasons. Most commonly, horse owners use this procedure for older, genetically superior mares that no longer have the uterine competency to maintain a pregnancy. By transferring an embryo into a younger, reproductively sound mare, this gives a means of continuing with an older mare’s breeding career. Owners of competition mares also find an embryo transfer program quite advantageous. This service allows a mare to continue showing and performing while still having one or more offspring every year. Given that the embryo is recovered early in development, there is potentially time to recover multiple embryos during a breeding season thus obtaining more than one pregnancy from a single mare per year. Embryo transfer services also benefit owners of 2-yr-old mares too immature to carry offspring or owners of late-foaling mares that want to get started earlier the following breeding season without losing a foal crop.

The Practical Aspects

In the event that a local veterinarian has experience with embryo recovery procedures, the donor mare can remain on-the-farm for breeding purposes allowing the veterinarian to perform the recovery either on-the-farm or at a nearby clinic. An embryo can then be sent to ERC via airlines or federal express and transferred into a recipient mare maintained at our facility. If there is no veterinarian in close proximity that is skilled with this technique, then the mare can be shipped to ERC where all breeding, embryo recovery and transfer procedures can take place. Owners situated relatively close to ERC may elect to breed their mare on-the-farm and then transport her to our facility just for the embryo transfer procedure.

The Process

Mares are monitored closely to determine the appropriate time for breeding and subsequent ovulation. Seven (7) to 8.5 days after ovulation, a foley catheter is passed into the vagina, through the cervix and into the uterine body. Embryo flush media is then repeatedly flushed into and out of the uterus, as rectal manipulation of the uterus is being performed. The hope is that if fertilization did occur, any embryo will be recovered through a filter cup system upon exiting out of the mare. If microscopic evaluation confirms the presence of an embryo then it will be non-surgically passed into a recipient’s uterus via the vagina.

ERC’s Program

ERC offers 6 different options to its embryo transfer program. Options are offered based on whether or not the client chooses to send the donor mare to ERC for management and embryo recovery or the embryos will be shipped to ERC. Also, clients have the option of using one of their mares to serve as a recipient or take advantage of the in-house recipient herd that ERC maintains. Embryos can also be preserved through a process called vitrification and kept in storage for transfer at a future date.