Effects of warming procedures on the survivability of in vitro matured buffalo (Bubalus bubalis) oocytes vitrified by Cryotop

The aim of this work was to evaluate the effects of different warming procedures on the survivability of buffalo in vitro matured oocytes vitrified by the Cryotop (CT) method. In vitro matured oocytes were vitrified in a final solution of 20 % ethylene glycol (EG), 20 % of dimethyl sulfoxide (DMSO) and 0.5 M sucrose. In Group A oocytes (n = 111) were warmed in 1.25 M sucrose for 1 min and then exposed to decreasing concentrations of the sugar (0.625, 0.42 and 0.32 M for 30 sec). In Group B, oocytes (n = 122) were warmed into a 0.25 M sucrose solution for 1 min, and then exposed to a 0.15 M sucrose solution for 5 min. Oocytes were rinsed and allocated into the in vitro maturation (IVM) drops for 2 h and then fertilized in vitro. The survival rate was significantly higher in Group A compared to Group B both at 2 h post-warming (92.8 vs 83.6 %; P<0.05) and at 20 h post-warming (85.6 vs 50 %; P<0.01). Cleavage rate was also significantly increased in Group A compared to Group B (55.3 vs 36.3 %; P<0.01) whereas no differences were observed in the blastocyst yield between groups (7.8 % vs 6.9 %).