You’ve probably heard about embryo transfer in horses or know a breeder who has tried it. You have your own mares and are wondering if it’s an option for you. What factors should be considered, and what does it entail?

To begin with, some breed registries allow embryo transfer, and some don’t. So before you go very far, check with your breed organization to find out the rules and regulations.

Betsy Smith and Gunnar Lund breed Hanoverian horses at their Halls Choice Farm, a 35-acre farm in New Market, Maryland. They decided to pursue embryo transfer with their prized mare, EM Femme Fatale (Wertherson x Emilyze, by Eminenz)—a 12-year-old gray who is currently competing at Prix St. George. She had one foal naturally when she was a 4-year-old and the rest have come through embryo transfer. According to the U.S. Dressage Federation, the mare is the leading producer of USDFBC Series finalists from 2000 to 2003, with six total.

Smith feels that embryo transfer should be reserved for the best performance mares and sires, or if the mare is older or can’t carry a foal to term for non-genetic reasons. The mare should be free of genetic defects, have an outstanding pedigree, temperament and trainability, as well as high quality gaits and a proven performance record. Embryo transfer is a serious investment of time and money, so it’s important to weigh the benefits versus the costs and risks involved.

What Is It?

Embryo transfer, in basic terms, occurs when a fertilized egg is removed from a donor mare and placed into a recipient mare to carry the foal to term. Sound simple? Not really. There are many steps to the procedure, it is expensive ($5,500 to $7,500), and carries a success rate between 50 and 60 percent. It requires highly trained personnel to perform the service, you may have to lease or purchase a recipient mare, and you need to transport the embryo to the recipient or vice versa. Smith points out that you only have a several-month window each year to attempt the procedure, and it is difficult and stressful for the mare. She has to be checked frequently, take additional medications, breed with artificial insemination, travel to the vet and have the embryos removed. Therefore, it is extremely important to keep the mare’s nutrition, weight and health at optimum levels.

If your mare is going to continue training and competing, it becomes an even more difficult balancing act. Smith sees it as an overall team effort. Everyone needs to invest the necessary time, and the trainer must work with the breeding schedule and make adjustments when necessary.

Much of the research and technique development of embryo transfer has been done at Colorado State University (CSU) in Fort Collins, Colo., headed by Dr. Edward Squires. Once donor and recipient mares have been selected, the donor mare is given a reproductive exam. The size and tone of the uterus and the size, shape and tone of the cervix are evaluated. A uterine culture is obtained and if there is no evidence of infection, the mare is bred on the second or third day of estrus and then again every other day until estrus ends. The goal is to breed the mare the day before and the day of ovulation. Six to eight days after ovulation, an attempt is made to recover the embryo by infusing fluid and then recovering it from the uterus. Once the fluid is examined under a microscope and the embryo located, it is rinsed and maintained in a culture dish at room temperature until transfer. If the transfer involves a fresh embryo, it is recommended that the procedure take place within two hours of collection. It is also possible to cool the embryo and use it up to 24 hours later.

The Substitute

The next portion of the procedure deals with the recipient mare. There are recipient herds throughout the country that specialize in embryo transfer. A recipient mare should weigh 900 to 1200 pounds, be 3 to 15 years old and have some basic ground manners. Smith maintains her own herd of surrogates. She prefers draft horses because of their size. They typically have a large uterus and produce a lot of milk. If you need to lease or purchase a recipient that will be factored into your overall costs as well. This mare also needs a complete reproductive exam. If any problems are found, she should not be considered an appropriate recipient.

Once your mare is cycling regularly, the goal is to have her ovulate up to three days after the donor mare. Transferring the embryo can be done surgically or non-surgically. An ultrasound 15 days after insertion of the embryo will confirm pregnancy. If the mare is not pregnant, a second attempt can be made. However, if after two attempts the mare is not pregnant, that mare may not a suitable choice for a recipient.

Obviously it is helpful to synchronize the donor and recipient mare’s heat cycles as closely as possible. This can be done using artificial lighting and administering prostaglandin (such as Regu-Mate). The progesterone keeps the mares from coming into estrus and when it is removed, the mares should come into heat. However, even if the mares have the same first day of estrus, it does not guarantee that they will ovulate at the same time.

In the end, “you have to be really patient,” says Smith. However, with good people, a lot of hard work, and more than a bit of luck, you can successfully achieve your goal of having your mare continue her competitive career while producing a crop of future winners.