Biotechnological approaches to the preservation and use of bovine ovarian cumulus-oocyte complexes in the system of reproductive technologies

Aim. To study the effect of different concentrations of ethylene glycol and glycerin in equilibration and vitrifi cation solutions on 1) the viability and further development of frozen-thawed bovine ovarian cumulus-oocyte complexes (COCs), cryopreserved by vitrifi cation method, 2) on the effectiveness of inseminating mature oocytes, obtained from them, and 3) on the formation of embryos. Methods. Biotechnological, cryobiological, morphological, cytogenetic, and statistical methods, as well as methods of statistical data processing were used in the research. Results. The results of experimental studies on the effect of different concentrations of ethylene glycol and glycerin in the equilibration solution during cryopreservation of bovine ovarian COCs (n = 502) on their viability and further development after freezing-thawing are presented. We also show the results of the comparative analysis of cryoresistant properties of bovine ovarian COCs (n = 560) using different concentrations of ethylene glycol and glycerin, as cryoprotectants, in the vitrifi cation solution in terms of the viability and maturation of the oocytes, which originated from these COCs, up to metaphase II of meiosis. A comparative analysis of the application of ethylene glycol and glycerol in differ- ent concentrations for the equilibration and vitrifi cation solutions in cryopreserving bovine ovarian COCs (n = 220) demonstrated a relationship between the level of concentration of these cryoprotectants and the number of embryos after in vitro insemination of mature gametes, obtained from these frozen-thawed COCs. Conclusions. It was found that the use of 25 % ethylene glycol and 5 % glycerin in the equilibration solution and 10 % ethylene glycol and 40 % glycerin in the vitrifi cation solution during cryopreservation of bovine ovarian COCs ensures lower toxicity of these solutions and promotes more effi cient (up to 14.3 %) formation and development of embryos after in vitro insemina- tion of mature gametes, obtained from these COCs