Cryopreservation of porcine embryos:: state of the art

Long term storage of porcine embryos would be worthwhile both for the preservation of genetic resources and for exportation of genotypes around the world. Three methods are available: freezing, classical vitrification and Open Pulled Straw vitrification (OPS). The efficiency of these methods were mainly evaluated in vitro by the development of morulae and blastocysts and in vivo by the birth rate after transfer into recipients. Freezing involved addition of glycerol as the cryoprotectant, the temperature is slowly decreased with, at least one step. Despite some development in vitro, the in vivo survival after transfer of embryos up to the peri-hatching stage is lower than 5%. Ice crystal formation was considered to be responsible for the main damages to embryos. Vitrification that allows direct transition between liquid and vitreous phase was the second method developed. When combined with pre and post-cryopreservation treatments of the embryos, the in vivo survival rate rises up to 18.5%. The OPS method is characterised by a very high speed of vitrification and without any treatment of embryos, the in vivo survival of embryos was close to 30%. In conclusion, methods are now available for cryopreservation of porcine embryos and further improvements are expected for a better efficiency and practicability. (C) 2003 Elsevier B.V. All rights reserved.