Vitrification of immature bovine oocytes using glass micropipettes under normal or super-cooled LN Vitrification and thawing: Two vitrification solutions

Aim: To evaluate the developmental competence of post-thaw vitrified bovine cumulus-oocyte complexes (COCs) in vitro. Materials and Methods: A total of 129 COCs were cryopreserved using vitrification solution comprising of 15% ethylene glycol (EG) + 15% dimethyl sulfoxide (DMSO) + 0.6 M sucrose in medium TCM-199 with 10% FBS. Immediately, within a minute they are plunged into liquid nitrogen using 0.25 ml straws. Thawing was made with a step wise dilution method. Postthaw normal vitrified and non-vitrified oocytes were subjected to in vitro maturation and in vitro fertilization. Results: Post-thaw survival percentage of vitrified oocytes was 88.37% and maturation performance of vitrified oocytes on the basis of cumulus expansion was 81.58% as compared to non-vitrified control 93.85%. The in vitro fertilization performance of vitrified oocytes was 49.46% as compared to the non-vitrified ones (63.11%). Similarly, blastocyst formation of vitrified oocytes was 21.74% as compared to 32.47% in non-vitrified oocytes. Conclusion: Vitrification of immature bovine oocytes using 7.5% EG + 7.5% DMSO for equilibration and 15% EG +15% DMSO + 0.6 M sucrose as vitrification solution yielded better in vitro fertilization and blastocyst formation rate.