The Benefi ts of Freezing Embryos and Oocytes for Long-term Storage In laboratory animals, especially the mouse, advances in molecular genetics has permitted the creation of thousands of mutant mouse strains that are too expensive to maintain as live breeding colonies (1). As a result, an increasing number of genetically valuable mouse strains are preserved and “maintained” by freezing their embryos, oocytes and sperm. Embryo cryopreservation and transfer have become prominent in livestock industry (especially for large and small ruminant breeding) (2) to improve the propagation of genetically valuable individuals. In 2005, more than 370,000 frozen-thawed bovine embryos were transferred worldwide (2). At last, the benefi ts of cryopreserved oocytes and embryos are widely recognized for wild species conservation because frozen germ cells and embryos could serve as assurances against any unforeseen catastrophes and assist in the management of the populations both in zoos and in nature (3). However, the application of this technology in wildlife conservation is still far from being routinely used (4). So far, live offspring have been produced from frozen-thawed embryos only in less than a dozen of species (felids: ocelots, caracal, African wild cat; primates: macaque, baboon; ungulates: eland, red deer, fallow deer) (4).