Production of embryos by assisted reproduction in the horse.

The research focuses on developing methods for producing horse embryos outside the womb. Current in vitro fertilization techniques have been largely unsuccessful due to a low fertilization rate. Methods like oocyte recovery from living mares and transfer of matured oocytes have proven more successful, suggesting that improvements to in vitro fertilization and the harvesting of immature oocytes from mares might lead to better results in in vitro embryo production.

Methods of Oocyte Recovery

• The study has explored the process of oocyte recovery by aspiration of dominant preovulatory follicles in living mares; this approach involves the use of a trans-abdominal puncture.
• Researchers have also looked into retrieving oocytes by puncturing both preovulatory and immature follicles through the use of trans-vaginal ultrasound guidance.
• Embryos have been produced from isolated oocytes using these methods; however, further development of these techniques is necessary for the successful production of embryos in vitro.

Transfer of Matured Oocytes

• Further research was conducted on the transfer of in vivo-matured oocytes to the oviducts of bred recipient mares, which resulted in high rates of successful pregnancy between 75-85%.
• In contrast, there has been very limited research on the transfer of horse oocytes that have been matured in vitro.

Limits of In Vitro Maturation

• It has been found that recovery rates of immature oocytes from horses in vivo are significantly lower than those for cattle, posing a challenge for the application of similar methods in both species.
• Research on oocytes recovered from post-mortem horse ovaries has indicated that horse oocytes from smaller (< 20 mm in diameter) viable follicles might not yet be meiotically competent, meaning they are not yet capable of undergoing the cell division necessary for fertilization.

Future of In Vitro Embryo Production

• Before in vitro embryo production can become a practical clinical and research procedure in horses, methods for in vitro fertilization and for obtaining an adequate number of competent immature oocytes from mares must be developed.
• Overall, improvements in the techniques used to retrieve and mature oocytes, coupled with developments in in vitro fertilization methods, will be key to advancing the production of embryos in vitro in horses.