Embryo Transfer

Embryo Transfer? What is it? Why would I want to do it? How much is it going to cost me?

All great questions that can be considered in a horse breeding program. Basically embryo transfer is the transfer of an equine embryo from one mare to another. Most often it is considered in the case of a valuable but not breeding viable mare, meaning the mare for whatever reason can’t carry a foal to term. There are a wide variety of reasons a mare can’t carry to term such as age or physical condition. It can also be used to have more than one foal for a given mare or to be able to continue the show career of a mare and yet start her breeding career at the same time.  Most breed associations now allow registrations of multiple foals, with the exception of the Jockey Club for Thoroughbreds. Most of this information has come from Colorado State University.

The donor mare’s job is to conceive. The mare is bred either by natural cover or by artificial insemination there by conceiving an embryo. Most mares have an estrous cycle of 21 to 22 days, with the cycle beginning on the day of ovulation. Hormonal changes determine the cycle.  Keeping records on your mare’s estrus cycle will greatly help with the breeding of the mare, and may actually help cut down on costs. Timing is crucial for successful embryo transfer and ultrasound scanning is used to determine which stage the mare is in the cycle. Each ultrasound adds to the cost and if you know the approximate stage of the cycle you may be able to eliminate additional tests.

Colorado State University's Dirk Vanderwall, DVM, PhD, said, "We base all the procedures on the day the mare ovulated, as the age of the embryo is based on the day ovulation occurred, or Day Zero." When a mare conceives, the embryo first develops in the oviduct, then enters the uterus from 5 to 6 days after ovulation. Day 6 is the earliest date for embryo collection, when the embryo has most likely entered the uterine horn. At this date, the embryo is called a morula.

The collection process is non-surgical, performed by flushing the embryo from the uterine lumen. CSU technicians generally perform the uterine flush on Day 7. "We use a container full of a sterile salt solution, with some protein added," said Vanderwall. "We place a catheter through the vagina and through the cervix, and an inflatable cuff on the catheter provides a fluid-tight seal. The solution passes down through a tubing system into the uterine lumen.

"As the fluid swirls throughout the lumen and drains back out through gravity, it collects the embryo, which is swept back out. The fluid and embryo pass out through the tubing system, into and through an embryonic filter." The filter traps the embryo, and a technician examines the filter under a stereo dissection microscope. When the embryo is identified, it is removed into a more enriched medium until the time of transfer. At this point the embryo is about the size of a dust particle.

The surrogate or recipient dam must be ready to accept the embryo--her estrous cycle needs to be synchronized with the donor mare's cycle. The surrogate ovulates either one day prior, the same day, or one to three days after the donor mare. Colorado State University acquires and maintains a substantial number of recipient mares, certified through their age (three to 12) and a thorough reproductive examination. Their estrous cycles are recorded to match them with expected donor mares. If the cycles don't match, the laboratory uses hormonal therapy to synchronize ovulation.

Colorado State University transfers embryos using both surgical and non-surgical methods, with the surgical method resulting in higher pregnancy rates. Veterinarians perform a standing surgical process with the tranquilized surrogate mare standing in stocks. Under sterile conditions, the surgeon makes an incision in the recipient's flank, locates the uterus, and exteriorizes the uterine horn. The first pregnancy check on the recipient mare is day 11 of gestation (4 days after the transfer) and a definitive positive or negative is known by day 16 of gestation (9 days after transfer). If the mare is not pregnant the process must be repeated.

The transfer can either be done onsite or by shipping. For the onsite method you would have your mare at the transfer facility to be bred and flushed. For the shipped method you would have your mare at a breeding facility to be bred and then flushed having the embryo shipped to the transfer facility to be received by the recipient mare. Many transfer facilities maintain their own recipient mare herd, tracking their cycles, but you can provide your own recipient mare.

Size of the recipient mare compared to the embryo-donating mare is a consideration for choosing the recipient. Undergrowth or overgrowth of the fetus in utero may be maintained into maturity. Retarded growth within a smaller mare's uterus may present as physical and behavioral immaturity at birth. It can also delay a foal's time to stand and suckle.

The costs of each procedure should be stated when making the agreement for service, however the number of times each procedure has to be performed may vary for each mare making the costs of getting a foal by this method variable. The average costs of the procedures including lease of the recipient mare is about $5,000.00. This doesn't include any stallion fees, the transportation of the mares to and from the facility, and most recipient mare providers expect the mare to be returned within 6 months after foaling.

Obviously, embryo transfer is not for the average horse or horse owner, but if you find yourself in need of the service and blessed with the funds to make it happen, it is possible. The percentages of success are higher with younger mares, decreasing steadily with each passing year of a mare’s life. The rates of success for the facility you choose should definitely be a consideration when picking your location. Generally, if all parties considered (mare, stallion and recipient mare) in the breeding were at the same facility.

Anne Wicke is a Sampson County resident and NC Cooperative Extension certified REINS volunteer.  She is employed at Carroll’s Cutting Horses, a premier breeding operation located in Turkey, North Carolina.