Vitrification versus cryopreservation of embryos

Cryopreservation of embryos has yet to become common place in equine practice despite its obvious potential for optimising and simplifying recipient mare management and facilitating long-term storage and long-distance transport of embryos. A number of inter-related factors have contributed to the slow up-take of horse embryo cryopreservation, these include; (1) the absence of effective, commercially available products for stimulating multiple ovulation; (2) poor pregnancy rates following cryopreservation of embryos >300 µm in diameter; (3) difficulty in recovering embryos at early developmental stages amenable to cryopreservation; and (4) inter-embryo variation in susceptibility to cryodamage. However, acceptable success rates (>55% pregnancy) have been reported for both slowfrozen and vitrified small embryos (<300 µm), and recently for larger expanded blastocysts following puncture and aspiration of blastocoel fluid ...