Stage-specific effects of osmolarity of a culture medium on development of pig oocytes and miniature pig somatic cell nuclear transfer embryos activated by ultrasound treatment

Whether high osmolarity of a culture medium at the early culture stage affects the development of pig oocytes and miniature pig somatic cell nuclear transfer (SCNT) embryos activated by ultrasound was examined. When oocytes were cultured in modified porcine zygote medium-3 (mPZM-3) with increased NaCl to 138 mmol/L (mPZM-3+NaCl; 326 mOsm) or 50 mmol/L sucrose (mPZM-3+sucrose; 318 mOsm) for the first 2 days and then cultured in normal mPZM-3 (273 mOsm) for 5 days, the cleavage and blastocyst formation rates were significantly (P < 0.05) higher than those of oocytes cultured in mPZM-3 for 7 days. The cleavage and blastocyst formation rates of SCNT embryos cultured in mPZM-3+NaCl for the first 2 days and then cultured in mPZM-3 for 5 days were also significantly (P < 0.05) higher than those of embryos cultured in mPZM-3 for 7 days. These results showed that the high osmolarity of a culture medium induced by increasing NaCl concentration during the first 2 days improves the development of pig oocytes and miniature pig SCNT embryos activated by ultrasound.