Embryo Transfer

Embryo transfer is a reproductive technique that allows the collection of an embryo from a donor mare when the embryo is seven to eight days old. The embryo is then transferred into a recipient (surrogate) mare where the pregnancy can then be carried to term.

Most people consider the biggest benefit of embryo transfer to be that it allows performance mares to have a foal while still remaining in training/competition. Depending on the breed registry, multiple foals can be produced from a single mare in one season. Another advantage to this technique is that it allows mares that are unable to carry a pregnancy on their own (due to physical or reproductive abnormalities) to reproduce successfully. Embryo transfer can help to maximize the number of foals produced from mares with high quality genetics or impressive performance records during their reproductive lifetime.

Embryo transfer requires both a donor mare, and ideally two, or three recipient mares that are synchronized in their estrous cycles. This maximizes the chance that one of the recipient mares will match the donor mare’s heat cycle. All mares should be healthy, reproductively sound and cycling regularly. An ideal recipient mare should be less than 9 years old, be of good physical/reproductive health and temperament.

First, the donor mare is bred normally (AI, live cover) with special attention given to the time of ovulation and to ensure an excellent uterine environment. Seven or eight days after the donor mare has ovulated her uterus is flushed to recover the embryo. Several liters of flush media are warmed and infused into the uterus through a catheter. The uterus is flushed three or four times and drained through a filtered collection bottle. The collected embryo is washed to remove any contaminants and evaluated for viability based on the size, grade, morphology and developmental stage.

Next, the embryo is transferred to the recipient mare. It is important that the recipient mare has ovulated no more than one day before, or two days after the donor mare. The embryo is placed in an insemination gun and transferred into the uterus while palpating these structures rectally. The initial pregnancy exam of the recipient mare will be conducted 4 days after the transfer.

It is very important for a successful embryo transfer to use good quality semen from known fertile stallions. If the donor mare is pregnant, the embryo will be recovered in over 95% of cases. Once an embryo is recovered, the transfer success rate is dependent on the quality of the embryo. High quality embryos will result in pregnancy in 70 to 80% of cases.

Embryo transfer is not a viable option for all mares, so it is important to speak to your veterinarian and determine if this is a possibility for your breeding program. When dealing with embryo transfer, preparation is the key to success – let us help you cover every detail!