Experiments were conducted on the morphology, fertilization and embryo development rate of vitrified ovine oocytes matured in vitro. Three vitrification solutions were used for vitrification. PBS supplemented with 1% BSA, 30% ethylene glycol was added by one of three different sucrose concentrations, 1.00 M (VS 1 ), 0.50 M (VS 2 ), and 0.25 M (VS 3 ). The results showed that the percentages of normal vitrified oocytes after warming were 78 and 63% in VS 1 and VS 2 , respectively, which was

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... ficantly higher as compared for VS 3 . The fertilization rates were 59 and 66% in VS 1 and VS 2 , respectively, which were also significantly higher as compared with VS 3 (35%). Zygote viability after 18 h was 57; 43; and 40%, for VS 1 ,VS 2 , and VS 3 , respectively, which was not significantly different. The incidence of polyspermic penetration increased with increasing sucrose concentration, i.e 23, 11, and 9% in VS 1 , VS 2 , and VS 3 , respectively, as compared with unvitrified oocytes (4%). The cleavage rate of vitrified oocytes in VS 1 was 13.2% which was significantly lower (p<0.05) compared to those of unvitrified control oocytes (70.0%). Hence, a high sucrose concentration is beneficial for maintaining the oocyte structure during the processes of vitrification and thawing, which ultimately results in increased in vitro fertilization rates.