Post thaw in vitro maturation of vitrified immature oocytes in sheep using different cryoprotectant concentrations

The present study was conducted to evaluate different cryoprotectant concentrations on post-thaw in vitro maturation rate of vitrified sheep oocytes.Vitrification was done in three vitrification solutions using different concentration of cryoprotectants (Ethylene Glycol + DMSO in equal ratio) i.e. (G1) 20%, (G2) 30%, (G3) 40% mixture of ethylene glycol and DMSO in equal ratio in open pulled straw. Post thaw IVM rate was evaluated based on cumulus cell expansion after 1 week of storage in LN2 and D2 cumulus cell expansion was considered as mature oocytes. In the present study, 152, 152 and 125 oocytes were recovered post thaw with 133,141,117 morphologically normal oocytes in G1 (20%), G2 (30%) and G3 (40%) respectively, which were then subjected to IVM. Significantly, higher percentage of in vitro maturation rate of post thaw oocytes based on D2 cumulus cell expansion was observed in G1 i.e. 20% (48.87%) followed by G2 i.e. 30% (32.6%) with lowest percentage in G3 i.e. 40% (26.4%) respectively. However, non-significantly higher percentage of oocytes was found with D1 expansion in 30% (11.34%) followed by 40% (8.5%) and 20% (5.26%) group. In conclusion, lower cryoprotectant concentrations (20%) of ethylene glycol and DMSO increases the maturation rate of vitrified immature oocytes in sheep possibly due to decreased toxic effect of cryoprotectants.