Effect of type of cryoprotectant on morphology and developmental competence of in vitro-matured buffalo (Bubalus bubalis) oocytes subjected to slow freezing or vitrification.

The present study examined the effects of different cryoprotectants on morphology and developmental competence of in vitro-matured buffalo oocytes after slow freezing or vitrification. After slow freezing in dimethyl sulfoxide (DMSO), ethylene glycol (EG) or 1,2-propanediol (PROH), at 1.0 or 1.5 m each, the proportion of morphologically normal oocytes recovered was significantly higher (P < 0.05) with 1.5 than 1.0 m for all cryoprotectants and was highest (P < 0.05) for 1.5 m DMSO. Following vitrification, the percentage of morphologically normal oocytes recovered was lower (P < 0.01) for 40% EG than for 40% DMSO, 20% EG + 20% DMSO or 20% EG + 20% PROH. The most common damage, irrespective of the cryopreservation method, was loss of cumulus mass. The cleavage rate and the proportion of vitrified-warmed oocytes that developed to morulae/blastocysts were significantly higher (P < 0.01) for 20% EG + 20% DMSO than for the other groups. A higher proportion of oocytes developed to morulae (11.5% v. 4.3%) or blastocysts (5.4% v. 0.6%) after vitrification in 20% EG + 20% DMSO than after slow freezing in 1.5 m DMSO. In conclusion, vitrification was more effective than slow freezing for the cryopreservation of in vitro-matured buffalo oocytes.