Breeding horses has come a long ways in the last 50 years. Veterinarians have been able to overcome many of the obstacles presented when breeding horses with advancements in artificial insemination and embryo transfer. However, there are still times when infertility of either the mare, stallion or both prevent getting foals on the ground. The most recent advances in assisted reproductive technologies, Ovum Pickup and Intra-Cytoplasmic Sperm Injection (ICSI), have allowed us at Weatherford Equine Breeding Center (WEBC) to take the next step in overcoming these obstacles with some promising results.
Ovum Pickup
Ovum pickup, also known as oocyte aspiration or oocyte collection, is the process by which oocytes (eggs) are retrieved directly from a mares ovaries via transvaginal aspiration (TVA). In this procedure a long needle is passed through the mares vagina to aspirate follicles present on the ovary using ultrasound guidance. At Weatherford Equine the TVA is performed with the mare standing under sedation and takes 15-60 minutes depending on how many follicles are to be aspirated. We will often do TVAs as outpatient procedures and work with referring veterinarians to coordinate optimum times for aspiration.
There are currently two approaches to oocyte collection. One approach is the collection of mature oocytes. This is done by aspirating a large dominant follicle right before it ovulates and typically only one follicle is aspirated per cycle.
The other approach is the collection of immature oocytes. In this approach all the follicles that are present on the ovary at the time of the procedure can be aspirated regardless of size because the mare does not need to be cycling. This approach results in a much higher number of oocytes retrieved but they must be matured in the lab. Statistically, the immature oocyte collection results in more pregnancies per aspiration but each mare is different and results may vary. At WEBC, we have performed both types of egg retrieval with success. Each approach has specific aspiration and handling requirements which are important to the success of the procedure.
Once the oocytes are collected they can be shipped to an Intracytoplasmic Sperm Injection (ICSI) lab. It is important to have the oocytes collected by a knowledgeable oocyte aspiration facility which is comfortable with the processing, packaging and shipping of oocytes. Several studies have shown that shipping oocytes has limited negative effects on embryo production. This allows mares to be aspirated closer to home and avoids having them hauled long distances to an ICSI lab location.
Intracytoplasmic Sperm Injection (ICSI)
Once at the lab the immature eggs are matured in special media. Once mature, they are fertilized using ICSI. This procedure is performed by injecting a single sperm cell directly into an egg. If a mature oocyte was recovered it is immediately injected because the maturation process has already taken place within the mare. The resulting fertilized egg is then cultured in the lab until it becomes a transferable embryo (typically 6-8 days) at which point it can be shipped to an embryo transfer facility or vitrified (frozen) for later use. There are currently only a handful of ICSI labs in the United States which are successful with equine oocytes.
At WEBC we are most often utilizing oocyte aspiration and ICSI for high value stallions that have a limited supply of semen. By using only a fraction of semen to fertilize eggs we have been able to help stallion owners be more efficient with semen supplies. For example, one dose of frozen semen (typically 8 straws) can be thawed and refrozen into 800 ICSI doses. It is for this reason that “ICSI Only” contracts have become common for stallions that are dead or have become infertile due to age. We have also seen success using these procedures for mares that are no longer able to produce embryos via embryo transfer. Since the oocytes are taken directly from the mares ovary we are able to completely take the uterus, cervix, etc... out of the equation.
The success rate for oocyte aspiration and ICSI can be highly variable but in the past couple of years WEBC has averaged one embryo per immature aspiration and one embryo for every three mature aspirations. As with any new technology there is still a lot of information to be gained but we have done enough aspirations that we are comfortable saying this is a legitimate technology for the commercial breeding industry.
Ovum pickup is offered by several SBS Affiliate laboratories. Click here to find an SBS affiliate lab near you.
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