Vitrification of bovine oocytes and its application to intergeneric somatic cell nucleus transfer

We determined the efficacy of a microdrop vitrification procedure for cryopreservation of bovine oocytes, using vitrified oocytes as cytoplasts for intraspecies and intergeneric somatic cell nucleus transfer (NT). In vitro matured bovine MII oocytes were vitrified in microdrops with a vitrification solution containing 35% ethylene glycol, 5% polyvinyl pyrrolidone, and 0.4 M trehalose. After warming, approximately 80% of the vitrified oocytes were morphologically normal, and their enucleation rate was similar to that of fresh oocytes. The NT embryos constructed with bovine cumulus cells and the vitrified oocytes developed similar to blastocysts constructed with fresh oocytes, although the cell number of NT blastocysts originating from vitrified oocytes was lower than that of the fresh control. In a second experiment, we examined the development of NT embryos constructed with vitrified bovine oocytes and bovine fibroblasts (intraspecies NT embryos) or swamp buffalo fibroblasts (intergeneric NT embryos). There were no differences between the intraspecies and intergeneric NT embryos in fusion, cleavage and development to blastocysts, except for lower cell numbers in the intergeneric NT blastocysts. In conclusion, the efficacy of this microdrop vitrification procedure and the production of swamp buffalo NT blastocysts using vitrified bovine oocytes was demonstrated.