The study looked at freezing sheep embryos at different stages of development using two methods: slow freezing and ultra-fast vitrification. They found that morula/blastocyst stage embryos had better survival rates after thawing compared to early embryos. Fresh embryos had higher survival rates than frozen ones, with the best survival seen in morula and blastocyst stage embryos. Overall, the method of freezing and the stage of embryo development did not affect the preservation of embryo structure or survival rates after transfer to recipients.