mares – Palm Beach Equine Clinic

By Lindsay Berreth / Jump Media

With modern veterinary technology, there are several ways to breed your treasured mare should she have trouble getting pregnant or carrying a foal. Intracytoplasmic sperm injection, or ICSI, an alternative to traditional embryo transfer is becoming a popular option for the sport horse mare.

According to Dr. Justin McNaughten BVMS, DACT, the equine reproductive specialist at Palm Beach Equine Clinic (PBEC) in Wellington, FL, the ICSI procedure was originally developed to help overcome subfertility in mares and stallions. The first ICSI foal was born in 1996, and since then the procedure has gained popularity amongst breeders for mare and stallion owners alike.

Before ICSI, many breeders’ options for their mare were limited to embryo transfer, which involves breeding the donor mare, flushing the donor mare’s uterus, and then transferring the embryo into a recipient mare that has been synchronized to the donor mare’s cycle. For stallions with limited semen reserves, there wasn’t much that could be done. However, ICSI has become an invaluable tool for preserving sperm from deceased stallions or stallions with limited semen availability as the procedure uses less sperm to fertilize an egg.

A significant advantage of ICSI for sport horse mares, compared to traditional embryo transfer, is that the procedure can be performed at any stage of the estrous cycle, regardless of the natural breeding season. This flexibility allows mares to concentrate on their competition schedules and minimizes disruptions to their training or show commitments.

During the procedure, oocytes, or eggs, are collected from a donor mare’s follicles on the ovary. “It is a valuable option for mares with uterine, oviductal, or cervical disorders that would not allow the mare to be an embryo donor,” said Dr. McNaughten. The ICSI procedure bypasses most of the reproductive tract and goes straight to the source for the oocytes (shown below), the ovary.

Palm Beach Equine Clinic offers the first stage of the procedure, the oocyte aspiration or egg retrieval. Vets will ship the eggs to an ICSI lab to complete the maturation and fertilization processes. During aspiration, mares are sedated and restrained in stocks. The veterinarian passes a long handle ultrasound probe which also houses the aspiration needle into the mare’s vagina. The ovary is stabilized by the veterinarian per rectum to allow for visualization of the ovary and the follicle. The needle is inserted into the follicle; the fluid is aspirated, the wall of the follicle is scraped, then the follicle is flushed and the fluid is aspirated. The scrapping, flushing, and aspirating are repeated multiple times to help dislodge the immature oocyte. The flush fluid that is recovered is then filtered, and any oocytes that are recovered are prepared and transferred into a special holding and shipped off for the next step. The entire process is known as transvaginal oocyte aspiration (TVA) in the US or ovum pick-up (OPU) in other parts of the world.

While the procedure is becoming more routine, it does carry some risks. To safeguard against any risks the procedure is only performed at the clinic. All mares are provided pain relief during the procedure and the following day. “We recommend that mares stay overnight at the clinic to be monitored for any signs of discomfort,” noted Dr. McNaughten, “and most mares return to full work within the week following the procedure.”

Once an ICSI lab receives the egg or eggs, they are put into a maturation media and monitored for 24 hours. “The eggs that we’re taking from the mare are immature, they’re incubated in a specialized maturation media,” said Dr. McNaughten. Each oocyte that matures, is then fertilized with a single sperm cell. “That’s the process of the intracytoplasmic sperm injection or ICSI. If all goes well, the fertilized oocytes are monitored to see if there’s any cellular division or cleavage, which means that fertilization was successful. Those will be monitored for the next 7-10 days until they reach the blastocyst or embryo stage.”

Maturation, fertilization, and embryo production rates can be affected by numerous factors including bred, age, season, level of work, semen quality and whether it is cool shipped or frozen semen. On average 50 to 60% of eggs will mature and be suitable for fertilization. Intracytoplasmic sperm injection laboratories report 70 to 80% of oocytes fertilized typically divide and grow, and 20 to 30% of fertilized oocytes will grow in culture to the blastocyst stage for embryo transfer. The final step in the ICSI process is to transfer the embryo to a recipient mare or freeze it. According to Dr. McNaughten, 60 to 70% of transfers are successful.

In our hands ICSI has become an invaluable tool for in vitro produced embryos not only on the mare side but for select valuable stallions. “To put it into perspective, in a conventional frozen semen breeding dose, the minimum dose is 250 million progressively motile sperm for one breeding. With ICSI, one sperm is used to fertilize one egg,” he explained. “We have also been very successful in producing embryos and foals using frozen semen from a deceased stallions that previously had not produced embryos through conventional breeding management with the same frozen semen.”

Palm Beach Equine Clinic is here to help you achieve your breeding goals. Our veterinarians specialize in breeding and reproduction and utilize the latest technology to ensure a seamless experience for both you and your mare. Contact us today at 561-793-1599 to schedule an appointment or to learn more.