PRODUCTION OF EMBRYOS BY ASSISTED REPRODUCTION IN THE HORSE

In vitro embryo production is not yet successful in the horse, largely due to low rates of fertilization in vitro. However, methods to produ ce embryos from isolated oocytes have been developed. Oocytes may be r ecovered from living mares by aspiration of the dominant preovulatory follicle by trans-abdominal puncture, and from both preovulatory and i mmature follicles by trans-vaginal ultrasound-guided puncture. Transfe r of in vivo-matured oocytes to the oviducts of bred recipient mares h as resulted in good pregnancy rates (75-85%). Little work has been don e on transfer of horse oocytes matured in vitro. Recovery rates of imm ature oocytes from mares in vivo are lower than those for cattle. In a ddition, work on oocytes recovered from horse ovaries post-mortem has shown that horse oocytes from smaller (<20 mm diameter) viable follicl es may not vet be meiotically competent. Methods for in vitro fertiliz ation and for obtaining adequate numbers of competent immature oocytes from the mare must be developed before in vitro embryo production can become a useful clinical and research procedure in the horse. (C) 199 8 by Elsevier Science Inc.