Cryopreservation of pig embryos.

The changing global needs for food and animal products require the development of breeding strategies for maximizing genetic improvement while maintaining genetic diversity. Genetic diversity can be conserved by using separate breeding herds; however, they may be expensive to maintain and inbreeding becomes a major concern. Alternative methods are needed to preserve valuable genetic resources in a reasonable and economic manner. Embryo cryopreservation allows indefinite storage in vitro at subambient temperatures where metabolism and other cellular functions are greatly reduced or cease, and upon recovery from storage, normal developmental competence can be resumed. Storage and transportation require little maintenance and there is no expense in animal care and little concern about disease transmission. Although there are methods for routine cryopreservation of germplasm and embryos of most livestock species, development of this technology in the pig industry is far behind and has abated improvements in genetic potential. Pig embryos are very sensitive to hypothermic conditions, and this limits their ability to withstand many conventional methods of preservation. Much research has focused on the high lipid content of pig embryos, and its role in hypothermic sensitivity and cryosurvival. Many studies have reported the conventional freezing of pig embryos, and vitrification has shown promise of eluding the difficulties associated with cooling sensitivity and ice crystallization. Recent research suggests that the embryonic cytoskeleton is susceptible to damage during cryopreservation, and this cellular disruption may be averted by using cytoskeletal stabilizers before preservation. Embryos cryopreserved by conventional freezing and vitrification under the influence of cytoskeletal stabilization have resulted in pregnancies or live offspring from recipient females after surgical transfer. Although cryopreservation technology is less advanced in pigs than in other livestock species, promising research shows evidence that researchers are close to achieving a methodology for preserving pig embryos.