Embryo Transfer in Horses

Consider these scenarios:

• You have a wonderful mare that’s winning at all the shows. You would love to have a foal or two from her, but you don’t want to take her out of competition for a whole season.
• Your friend’s best broodmare has some good breeding years left, but she has had a knee injury and the veterinarian advises she’ll be uncomfortable with the added body weight of pregnancy.
• You have been offered a nice mare that had a difficult delivery last year. Damage to her reproductive tract would make future births problematic.

These three hypothetical situations could have a common solution: embryo transfer. With this reproductive technique, a foal can be produced from a particular mare even though she will not physically carry and give birth to a baby.

The first step in embryo transplant is to allow the donor mare (biological dam) to ovulate, after which she is artificially inseminated with semen from the stallion of choice. Because the fertilized ovum does not implant immediately in the mare’s uterus, there is a window of several days during which the developing embryo can be flushed out of the donor mare’s uterus and placed in the uterus of a recipient mare. This second mare will have had her reproductive cycle synchronized with that of the donor mare so that she will be receptive to the embryo, allowing it to implant and develop.

To achieve a successful pregnancy by embryo transfer, it’s necessary to pay close attention to several factors. First, owners of both mares must be in communication with each other and with the attending veterinarian. This should be set up several months before the breeding date to allow the option of using drugs to induce ovulation. Ideally, both the donor and recipient mares are at the same location, so that their reproductive status can be synchronized and followed. When the breeding time approaches, the donor mare’s manager needs to be certain of her time of ovulation; semen of excellent quality must be obtained and used at the proper time; sterile procedures must be followed when retrieving and transferring the embryo; and both mares must have proper nutrition, be in good body condition, and be free of uterine infection or inflammation. The recipient mare will need to be checked in a few weeks to verify that the embryo has implanted and the pregnancy is off to a good start.

Owners who are interested in reproduction by embryo transfer should consult with several equine clinics that offer this service. If all goes well, a few months of planning can result in an uninterrupted schedule for the donor mare as well as a promising foal next spring.