Vitrification of sheep embryos and the viability of frozen / thawed embryos are tested with different parameters: apoptotic and anti-apoptotic genes, DNA integrity, expression of developmental specific genes. Vitrification of embryos in medium supplemented with anti-oxidants and cytoskeletal stabilizing substances and evaluation of survival with the determination of the above mentioned parameters. Vitrification of embryos in medium supplemented with anti-oxidant materials and evaluation of the viability with the determination of different parameters (see above).