Enhancement of cytoplasmic maturation of in vitro-matured pig oocytes by mechanical vibration

The effects of mechanical vibration during in vitro maturation and/or in vitro culture after artificial activation of pig oocytes on maturation and development were examined. In addition, the optimal conditions were applied to in vitro production of blastocysts derived from miniature pig somatic cell nuclear transfer (SCNT) embryos. Mechanical vibration during in vitro maturation did not affect the rates (60.5+-1.9-69.5+-2.2%) of oocytes reaching the metaphase-II stage. However, the blastocyst formation rates after activation of oocytes matured with mechanical vibration for 5 sec at intervals of 30-60 min or for 10 sec at intervals of 60 min were significantly (P0.05) higher than those of oocytes matured without mechanical vibration (25.7+-2.0-28.1+-2.7% vs. 12.3+-1.4% and 25.8+-1.8% vs. 15.7+-1.9%, respectively). In contrast, mechanical vibration during in vitro culture after activation did not affect the blastocyst formation (11.6+-5.2-16.5+-3.0%) of oocytes. Mechanical vibration for 5 sec at intervals of 60 min during in vitro maturation of oocytes did not affect fusion (66.8+-3.5-72.1+-3.1%) with miniature pig somatic cells after enucleation. However, the blastocyst formation rate of SCNT embryos was improved (P0.05) by mechanically vibrating recipient oocytes for 5 sec at intervals of 60 min during in vitro maturation, regardless of the presence or absence of the same treatment during in vitro culture (17.6+-2.5% vs. 9.4+-0.9% and 13.0+-0.3% vs. 7.4+-0.9%, respectively). The results indicated that mechanical vibration enhances the cytoplasmic maturation of in vitro-matured pig oocytes, resulting in improvement of their parthenogenetic development. In addition, it was shown that in vitro maturation of oocytes with mechanical vibration can be applied to efficient production of blastocysts derived from miniature pig SCNT embryos.