P-112: Potential Applications of Sheep Oocytes As Affected by Vitrification and In Vitro Aging

Background: The present study was carried out to investigate how the interactions between aging, vitrification, and post-warming interval affect the credibility of sheep MII-oocytes for in vitro fertilization (IVF), intracytoplasmic injection (ICSI), and parthenogenetic activation (PA). Materials and Methods: The vitrified-warmed oocytes, either immediately (immediate group: IG) or two hours post-warming (delayed group: DG) along with their corresponding unvitrified controls were used for assessment of (i) survival rate, (ii) meiotic spindle and chromosomal organization, (iii) ultrastructural changes, (iv) gene expression, (v) cortical granule release, and zona hardening and (vi) embryo development using IVF, ICSI, and PA. Results: According to our results, aged oocytes had significantly higher rates of chromosome and spindle abnormalities compared to young oocytes. However after vitrification-warming, the total rates of these abnormalities were not significantly different between aged and young oocytes. Unvitrified-aged, and vitrified young and aged oocytes had comparable ultrastructural characteristics whereas they were completely dissimilar in compared with unvitrified-young oocytes. Although mRNA abundance was reduced during vitrification-warming in both aged and young oocytes, the post-warming interval could improve the relative mRNA abundance. Aged oocytes had lower capacity for IVF and ICSI in compared with young oocytes, but had similar pattern for PA process. Conclusion: The vitrification process decreased developmental competence of both aged and young oocytes in compared with young ones, particularly when warmed oocytes were rested for 2 hours before IVF, ICSI and PA. The results of the present study showed that in vitro aged oocytes had higher capacity to be used for parthenogenetic studies rather than IVF and ICSI. Furthermore, it was shown that vitrified oocytes had a time dependent decline in quality and developmental potential. Notably, the speed of this decline was higher in vitrifiedyoung oocytes, indicating that the vitrified oocytes do not require to be rested post warming. Conclusively, the results of this study can be useful in preserving in vitro aged oocytes to provide a valuable and easy access source of oocytes for research purposed studies.