Cryopreservation of Mammalian Embryos: Slow Cooling

The benefits of banking mammalian embryos for long-term storage have long been recognized (1 ). Cryopreservation of gametes prevents genetic drift, offering a viable alternative to maintaining active breeding colonies while safeguarding the genetic integrity of scientifically valuable strains. This is of particular importance in the fields of mouse genetics and in the conservation of endangered species. It has been suggested that embryo cryopreservation will be critical for the preservation of endangered species if the genetic diversity of the small populations in captive breeding programs is to be maintained (2 ). The availability of stored genetic information in the form of embryos increases the generation time and allows the contribution of genetic material past the normal reproductive lifespan of the animal. The advances in the cryopreservation of domestic and laboratory animal embryos suggests that as knowledge of the basic reproductive physiology of exotic species increases, the establishment of embryo banks will become a reality (2 , 3 ). In addition, the ease with which frozen embryos can be transported is of great benefit, overcoming the necessity to transport live animals while reducing the likelihood of disease transmission.