Development of vitrified matured cattle oocytes after thawing and culture in vitro

Bovine oocytes were partly denuded either at the beginning (t(0)) or six ho urs (t(6)) after the beginning of maturation and vitrified by the open pull ed straw method at the end of the maturation process. After warming and fer tilisation, their development in vitro and in vivo was assessed. The rates of production of blastocysts achieved in vitro were 3-4 per cent for the t( 0) group and 0.9 per cent for the t(6) group compared with 40.4 per cent fo r the control oocytes. After transfer at the blastocyst stage pregnancies h ave been established in the three groups. Some of these pregnancies origina ted from vitrified oocytes which were further vitrified at the blastocyst s tage before being transferred into synchronised recipients.