Equine Embryo Transfer

: I own a top quality mare that I would love to have a foal out of. However, she is also my primary riding and competition mount, and I’d prefer not to stop riding her so she can have a foal. I do have another mare and am considering using her as a surrogate for embryo transfer. What exactly is involved in embryo transfer? How can I tell if my second mare is a good surrogate candidate?

A: Embryo transfer (ET) is perhaps the best option for this scenario. ET consists of breeding a top quality or special mare, called the donor mare, who will conceive and will carry her own pregnancy for about seven to eight days. At that time the small baby, called the embryo, will be removed (flushed) from the donor mare and will be transferred to a surrogate mare, called a recipient.

The donor mare must be available for breeding. Most people who have a top mare will prefer to breed her with frozen semen, which means that the mare will have to go to a breeding barn or clinic for three to five days.

The surrogate or recipient mare will be examined at the same time that the donor mare is examined for breeding and the cycles will be synchronized. That means that both mares will be ovulating at the same time so that when the baby is moved, the uterus of the recipient is under exactly the same hormones that the donor is.

The embryo at the time of transfer is only three-tenths of a millimeter in size, meaning we cannot see it before we flush the mare. The only way we will know it is there is by looking for it under a microscope. Most of the time, we only get one embryo per try. We