Usefulness of modified Medium RD as a chemically defined medium for in vitro maturation of bovine oocytes

PURPOSE: In the present study, I evaluated the usefulness of Medium RD, with mixed RPMI1640 and Dulbecco's modified Eagle's medium (1:1, v/v), as a chemically defined medium for in vitro maturation (IVM) of bovine oocytes. METHODS: In vitro maturation was performed in 10 mmol/L HEPES‐buffered TCM199 (mTCM199), 10 mmol/L HEPES‐buffered Medium RD (mRD), and mTCM199 supplemented with fetal bovine serum fraction (mTCM199 + FBS fraction) that served as control. Cumulus‐oocyte complexes were matured for 24 hours in three different media supplemented with follicle‐stimulating hormone, estradiol‐17β, and polyvinylpyrrolidone. Nuclear maturation of oocytes, their developmental competence into blastocysts after in vitro fertilization (IVF) and mitochondrial distribution in oocytes were investigated. RESULTS: There was no difference in the ratio of matured oocytes regardless of IVM media. The percentage of morula stage was higher in mRD than in mTCM199 group (P < .05) at 120‐144 hours after IVF, although the blastocyst rates between groups were not significantly different at 168‐216 hours. IVM in mRD increased the percentage of oocytes with diffused mitochondrial distribution compared with the immature and mTCM199 and had similar percentage of oocytes in mTCM199 + FBS fraction. CONCLUSIONS: Medium RD would be useful as a chemically defined medium for IVM of bovine oocytes.