Embryo Transfer Process

For those of you new to embryo transfer (ET) we would like to explain the program and procedures to you and describe how to best insure a successful outcome…a live foal (or foals) next year.

Your donor mare is carefully monitored through her estrous cycle and bred at the optimal time to either fresh, chilled and transported, or thawed/frozen semen. Her ovulations confirmed on the basis of ultrasound evaluation and then at precisely seven days post-ovulation the embryo is non-invasively lavaged out of her uterus. The fluid is then carefully filtered and examined microscopically. A seven-day embryo is typically less than 0.5-mm in diameter. Once we identify the embryo we assign it a quality grade (1=excellent through 4 = poor) which assists us in determining the best method of transfer and likelihood for successful implantation of this embryo.

The final step is when the embryo is transferred into an appropriately synchronized recipient mare’s uterus. This procedure is done non-surgically through the cervix. If all goes as planned the embryo will survive and implant into the recipient mare (surrogate mother) and she will carry the foal to term.

As you can well imagine, many factors enter into the formula for a successful embryo transfer program.

Quality Control of all stages of the process is paramount!

Seven day embryo as seen under the microscope in the center of the petri dish. This represents a good quality embryo in the expanded blastocyst stage.

In other words, not only must the donor mare be diligently teased, ultrasound examined, cultured if necessary, bred with her ovulation timed and recorded within 12 hours of its occurrence, but the same factors hold true for the monitoring of the recipient mare. This requires daily or optimally twice daily ultrasounds of the donor and recipient mare’s ovaries to determine the precise times of their respective ovulation(s).

Assuming a healthy and reproductively sound donor mare the overall odds of retrieving a high quality embryo are very good. If the mare has a rigorous show schedule or is sub-fertile due to age (>20 years) or uterine pathology (excessive fluid, infection, scar tissue) then the success rate diminishes somewhat. Breeding and flushing these difficult mares on multiple cycles is the best way to insure at least ONE pregnancy.

The recipient mare is an exceedingly important factor in determining the success of the program. Young, quiet, healthy mares with no reproductive problems or blemishes and good uterine biopsies are an absolute must. To settle for less is a sure way to invite disappointment and less than optimal pregnancy rates. Therefore, we recommend that you have available two suitable recipients for each donor mare or the choice of the best recipient from a large pool of approved mares such as the herd maintained at Pollyrich Farms. Lease or purchase options are available for these mares. Contact us for details on our recipient mare program.

Not to be overlooked, the selection of the stallion is also critical. Use of well proven, fertile stallions---whether using fresh semen or frozen semen--- is as important as donor and recipient selection. Keeping in mind that some stallions are still active on the show circuit one needs to be sure scheduling conflicts won’t arise in obtaining the semen at the proper time for the donor mare.

For any donor mares that are bred on farms other than under our direct supervision it is imperative to maintain good communication between your veterinarian and/or breeding manager and our staff. Scheduling of the ET needs to be done as soon as the donor mare ovulates so we can plan in advance to have the necessary time, materials and staff available.

If you have any questions, special circumstances, or need further explanations regarding any part of the ET program please don’t hesitate to contact us.

Candidates for Embryo Transfer

Mares of exceptional quality are able to produce more than one foal per year.
Competition mares can continue showing and still produce offspring.
Older mares, who can no longer reliably carry a pregnancy to term can still produce a foal.
Mares with medical problems that preclude maintaining a safe pregnancy can still produce a foal.

The overall odds of retrieving a high quality embryo are very good if you have a healthy and reproductively sound donor mare.