Embryo Transfer for Sport Mares: A Smart Breeding Solution
By Lindsay Berreth / Jump Media
If you have a performance mare that you wish to breed without interrupting her career, embryo transfer is a viable option. Palm Beach Equine Clinic (PBEC) in Wellington, FL, offers an extensive range of assisted and advanced reproductive procedures, including embryo transfer. With spring fast approaching, now is the time to plan.
PBEC President Dr. Scott Swerdlin highlights the advantages of the embryo transfer process, which has been utilized since the 1970s. This method is especially beneficial for sport horse mares that cannot afford to take time off for pregnancy. By using embryo transfer, you can continue riding your best mare while simultaneously breeding for your future champions. Additionally, embryo transfer is a viable option for mares with high genetic merit who cannot carry a foal. Some mares may have orthopedic issues that would be exacerbated by the extra weight of pregnancy, while others may have significant reproductive challenges, such as chronic uterine infections or a fibrotic uterus, which hinder their ability to conceive or support a developing pregnancy.
The first step in the embryo transfer process is embryo production. For this article, we are focusing on traditional in vivo embryo production vs in vitro embryo production. In vivo embryo production requires the donor mare to be bred, conceive, and produce an embryo that can then be transferred to a recipient mare. This necessitates the mare being off any hormones like Regumate® (altrenogest) or long-acting progesterone as they suppress the mare’s estrus cycle.
Strategic breeding management is essential to minimize disruptions to a mare’s training and competition schedule. This may include hormonal manipulation of the mare’s reproductive cycle, a series of reproductive examinations performed using transrectal palpation and ultrasound, a uterine culture and cytology, and breeding the mare by artificial insemination or via natural cover. It is also crucial to document the day and time of ovulation. Whether using fresh, cool-shipped, or frozen-thawed semen, the day and time of ovulation need to be documented to plan for the second and third steps of the process: embryo flush and transfer.
“Knowing the day of ovulation is important,” explained Dr. Swerdlin. “In the mare, fertilization and conception occur in the oviduct, where an embryo will remain for approximately 6 to 6.5 days before migrating to the uterus. Not knowing the day of ovulation might mean that the embryo is still in the oviduct at the time of the uterine flush. Conversely, if the embryo is further along in development, it becomes larger and more fragile, which decreases the chances of a successful outcome.”
To minimize disruptions to the mare’s schedule, most of the process can be performed on-farm, or owners can elect to come to PBEC on an outpatient basis. Veterinarians will closely monitor the mare’s estrus cycle to determine the optimum time for breeding, maximizing the chance of achieving a pregnancy.
“To improve our chance for success, once we determine that the mare is ready, the dominant pre-ovulatory follicle is stimulated to release the oocyte (egg) by administering an ovulatory agent,” stated Dr. Swerdlin. “This ovulatory agent mimics the mare’s naturally occurring hormonal process, and when used appropriately, the majority of mares will ovulate within 24 to 48 hours post-administration.
“Timing the insemination in relation to ovulation is key to success,” he continued. “This is especially true when using frozen semen. For mares that will be inseminated with frozen-thawed semen, we suggest that they arrive at the clinic the same day that the ovulatory agent is administered. This ensures that we can inseminate the mare as close to the point of ovulation as possible.”
The next step is embryo recovery, which is performed 6.5 to 8 days post-ovulation. “The mare will come to the clinic, and the process takes about an hour,” said Dr. Swerdlin. “During this procedure, the donor mare’s uterus is flushed with several liters of embryo flush media. This fluid is recovered and filtered through a special embryo filter to capture the embryo.”
After the embryo is retrieved, it is washed and graded to determine embryo quality. Embryos are graded on a 4-point scale, which 1 indicating excellent quality and 4 indicating a degenerate or dead embryo. Finally, the embryo is prepared for either direct transfer into a recipient mare, shipment to a recipient herd, or frozen for future use.
The final step in the process is the embryo transfer, which requires careful coordination. The success of this procedure is heavily dependent on selecting a suitable recipient mare, taking into account factors such as the mare’s age, size, maternal behavior, synchronization, and overall reproductive health.
“Owners can provide their own recipient mare, but we often recommend that mare owners utilize a leased recipient mare,” noted Dr. Swerdlin. “Numerous recipient herds are located throughout the country, with the closest ones being in the Ocala area. Currently, recipient mares are in very high demand, and each herd has a limited number of contracts available per year. One key advantage of using a recipient herd is that it allows multiple mares to be synchronized to match your individual mare’s ovulation date rather than relying on a single client-owned recipient. For those who prefer to use their own mare, our reproductive specialists at PBEC can manage the synchronization of the recipient mare and perform the embryo transfer.”
The embryo transfer procedure takes place at the clinic. The recipient mare is gently restrained in stocks with the aid of mild sedation. The embryo is carefully loaded into a transfer gun, which is guided trans-cervically into the mare’s uterus. Once the position has been confirmed, the embryo is deposited into the base of the uterine horn. A reproductive ultrasound is performed between three to seven days afterward to assess the uterine environment and confirm that the embryo is developing properly. Recipient herds will often report pregnancies between day seven to nine after transfer.
Dr. Swerdlin noted that the success rate for embryo recovery varies based on the type of semen used and the donor mare. “When using fresh and cool-shipped semen, embryo production rates can reach between 70% and 90%,” he said. “With frozen-thawed semen, the rates are lower, ranging from 50% to 60%. Overall, the success rate of the embryo transfer ranges from 70% to 90%, depending on the quality of both the recipient mare and the embryo.”
Embryo transfer provides an effective and practical solution for sport horse owners and breeders. As the demand for top sport horses increases, it continues to be a valuable tool for those looking to breed that special mare.
For more information on embryo transfer and other reproductive services offered at PBEC, visit www.equineclinic.com or call 561-793-1599.