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and opportunities here. I was really fortunate to get the position.”

Testing the Possibilities When Hinrichs accepted the offer to teach physiology at the CVM she began researching cloning and reproduction. She brought along Dr. Young Ho Choi as a collaborator, who began as a post-doctoral trainee and is currently a senior research scientist. The two began exploring the possibility of producing a fertilized equine embryo in vitro, a basic research and clinical tool in other species that was not yet feasible in the horse. In conventional IVF, sperm are placed in a dish with a mature oocyte, and one sperm penetrates the oocyte to fertilize it. Given ideal laboratory conditions, the egg will develop into an early embryo, which can be transferred to a recipient female for further development. However, traditional IVF had yet to be successfully achieved in horses. Unlike other livestock species, such as cattle, horse eggs and sperm do not seem to respond to traditional IVF methods. Therefore, Hinrichs and Choi took a different approach by looking into a more complex assisted reproduction method: ICSI . In ICSI, a single sperm is manually injected into the cytoplasm, the fluid that fills the cell, of the mature oocyte. It is then placed in an incubator in hopes that fertilization occurs and an early embryo can develop. The embryo can then be transferred into a recipient mare’s uterus for gestation. Because so few sperm are needed, in theory, a single straw of frozen semen from a valuable stallion can produce thousands of offspring. This means that deceased stallions can continue to reproduce so long as they have provided frozen sperm. Mares who are no longer able to reproduce naturally, but still produce healthy oocytes, can also continue to produce offspring through ICSI.

Overcoming Challenges and Moving Forward To see if the ICSI process could even be performed in their lab, Choi began working with a micromanipulator and a powerful microscope that allowed for manipulation of the horse oocyte. Using the micromanipulator, Choi was able to hold the oocyte in place and inject a single sperm into the egg through a pipette. This marked the beginning of a journey toward successful assisted reproduction for horses in vitro; but the rest of the journey would not be easy. After Hinrichs and Choi discovered that the ICSI process could be successfully performed to fertilize a horse oocyte in the lab, the next challenge was to provide the ideal conditions for an early embryo to develop—a goal that would take over two years to reach. “We could put the sperm into the oocyte, but we did not have the right environment for it to develop in vitro,” Hinrichs explained. “IVF had never worked in horses, so nobody had produced early equine embryos in the laboratory, so no one had done any studies on how you culture an equine embryo to get it to develop.” Promising results led to research support in the form of grants, which were instrumental in the success of Hinrichs’ 62 •

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Dr. Hinrichs and student

ICSI program. More funding led to more research, and Choi and Hinrichs discovered that an equine embryo needed a complex medium to grow for seven to 10 days until it could be placed in a recipient mare. After more successful attempts at producing early equine embryos in vitro, Hinrichs and Choi were able to move on to perform the process clinically. “It took a couple of years for us to develop a method where an embryo could develop in vitro to the point where we could transfer it to the uterus of a recipient mare to make a pregnancy,” Hinrichs said. “It turns out the developing equine embryo needs a lot to survive; it needs a complete cell culture medium. Luckily, you can buy a cell culture medium at the cell culture store. It’s got everything in it a cell would ever need.” The clinical ICSI program quickly became successful. In 2015 Hinrichs and Choi performed over 450 procedures on oocytes from valuable client-owned mares. A large part of this demand is due to low semen supplies of stallions who are deceased or too old to reproduce any longer. In comparison to other forms of assisted reproduction, such as artificial insemination, ICSI is more efficient in these cases. For example, artificial insemination of a mare with frozen semen could potentially take several straws of sperm to produce a pregnancy, while for ICSI, one straw of frozen sperm can be thawed and diluted so that it yields enough doses to perform hundreds of ICSI procedures. In addition to external grants, Hinrichs credits The Patsy Link Equine Research Endowment Fund as playing a major role in the success of her and Choi. “The Patsy Link endowment was what funded us to keep researching ICSI so that we could get the process to work,” Hinrichs

CVM Today - Winter 2017  

A semi-annual publication for the faculty, staff, students, alumni, and friends of the Texas A&M College of Veterinary Medicine & Biomedical...

CVM Today - Winter 2017  

A semi-annual publication for the faculty, staff, students, alumni, and friends of the Texas A&M College of Veterinary Medicine & Biomedical...