Abstract
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.
Highlights
Retrieval of a higher number of competent oocytes for in vitro maturation and in vitro fertilization (IVM – IVF) to obtain superior transferable bovine embryos coupled with development of freezing technique through vitrification will entail more productivity from the non descript animals
129 cumulus-oocyte complexes (COCs) were subjected to vitrification and the rest were non-vitrified and served as control
The sensitivity of bovine oocytes to cryo injury and consequent survival has been well described with variable results
Summary
Retrieval of a higher number of competent oocytes for in vitro maturation and in vitro fertilization (IVM – IVF) to obtain superior transferable bovine embryos coupled with development of freezing technique through vitrification will entail more productivity from the non descript animals. Unique characteristics of mammalian oocytes in respect of permeability of cryoprotectants and water through plasma membrane make them vulnerable for conventional freezing protocols as compared to embryo freezing. Recent advances in freezing techniques like vitrification procedure with modifications in equilibration time, concentration of cryoprotectants, volume and dilution protocol resulted in a higher survival of different stages of oocytes to maturation and fertilization in vitro [1]. The vitrification procedure for freezing technique of oocytes may be more advantageous as compared to conventional freezing protocol.
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