Embryo Transfers

Embryo transfer is the reproductive process in which an embryo (or embryos) is collected from the bred (donor) mare and then transferred to a recipient (surrogate) mare where a pregnancy can be established and carried to term. Embryo transfer has grown tremendously throughout the past few years and is recognized in many, but not all breeds. Before choosing embryo transfer as a preferred method of breeding it is recommended that contact be made to the breed registry to ensure the ability to register foals conceived and born in the embryo transfer process.

Advantages of Embryo Transfer

  • Many breeds approve the use of embryo transfer allowing more than one foal per year to be registered per mare. 
  • Embryo Transfer allows mares to remain on their race or show schedule with very little disruption. 
  • Embryo Transfer can be used for mares that are unable to carry a foal to full term. 
  • Embryo transfer can allow for young mares to produce embryos, yet avoid carrying the foal before they are physically mature enough to do so.

The Process 

Embryo transfer requires the synchronization of estrous cycles between the donor and recipient mare. After the donor mare is bred and ovulated, the transfer process can begin. The embryo flushing takes place 6-8 days from the day of ovulation, depending on the recommendation of the veterinarian and the history of the mares relative embryo size. The embryo is flushed out of the donor mare through a process in which an embryo catheter is passed through the vagina and cervix into the uterus. From there, tubing is attached to the catheter to allow the flow of sterile fluid into the uterus. Then, the uterus is massaged and the fluid is then drained into a filtered collection dish, examined under a microscope and recovered embryos are located.

Recovered embryos are then assessed as to developmental stage and the most viable embryo(s) are then transferred into a recipient mare through a process comparable to that of artificial insemination. Ultrasound can then be performed on the recipient 12-14 days after ovulation. Follow-up ultrasounds should also be done at 30 and 45 days to ensure that the recipient mare has not absorbed the embryo. The same ultrasound should be performed on the donor mare as well to confirm that no remaining embryo has lead to a developing pregnancy.