Developmental Competence of Frozen-thawed Germinal Vesical Porcine Oocytes by Vitrification Method following Maturation,Fertilization and Culture In Vitro

The purpose of this study was to evaluate the viability and subsequent developmental ability of porcine germinal vesicle（GV） oocytes vitrified step-wise exposure to cryoprotectants. Oocytes were transferred to a vitrification solution composed of 10% ethylene glycol（EG）,10% dimethyl sulfoxide（DMSO）, 300 g/L-1 Ficoll and 0.5 mol/L-1 sucrose（EDFS40） in a direct manner （non-preequilibrium） or in step-wise manner（ single- and two-step preequilibrium）. After vitrification and storage in liquid nitrogen, the oocytes were thawed,washed and in vitro maturation, fertilization and culture. In the non-preequilibrium group, the rates of post-thawed oocytes surviving, maturing to metaphase-Ⅱ, cleavage rate and blastocysts rate was significantly lower than that of sigle- and two-step preequilubrium groups（P<0.05）. In the single- and two- step groups, the rates of metaphase-Ⅱ stage were 46.8%, 42.7% and 49.7%, respectively, the rates which developed to blastocysts were 10.5%,11.1% and 14.8%, respectivaly. In the non-vitrified control group,the rates of oocytes maturing to metaphase-Ⅱ, developing to blastocysts was significantly higher than that vitrified groups（P<0.05）. The present study shows that the vitrification of porcine GV oocytes by a step-wise method involving two-steps preequilibrium may have advantage in maintaining the viability and subsequent production of blastocysts.