The presence of synthetic polymers in the maturation medium affects the cryotolerance and developmental capacity after parthenogenic activation of vitrified goat oocytes

The purpose of this present study is to assess if addition of the synthetic polymers in maturation medium can influence cryotolerance and subsequently embryonic development of mammalian oocytes. We examined the roles of two polymers, including polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP), on in vitro maturation (IVM), embryonic developmental capacity, and cryotolerance of goat oocytes. The present study includes two parts. At first, goat cumulus-oocyte complexes (COCs) were matured in a medium supplemented with 10% fetal bovine serum (FBS), 3 mg/ml PVP, or 1 mg/ml PVA, respectively. Data of oocyte with first polar body, cleavage, and blastocyst following parthenogenetic activation (PA) were recorded. Secondly, after maturation in the above medium, oocytes were vitrified using the Cryotop technique and then the morphology, cleavage and blastocyst formation of vitrified oocytes have been checked. The results demonstrated that the adding of PVP or PVA in maturation medium can't affect IVM of goat oocytes in comparison with FBS, as concern cumulus cell expansion, first polar body formation, and embryonic development. Additionally, without plunging into liquid nitrogen, only exposure to the vitrification and warming solutions cannot also influence the quality of oocytes, in terms of morphology, cleavage, and blastocyst formation. However, after IVM with synthetic polymers and vitrification, the ratio of oocytes with standard morphology in PVP or PVA group was only 59.47% ± 3.56% or 54.86% ± 5.19%, respectively, and was significantly less than that in the FBS group (89.37% ± 4.52%, P < 0.05). Furthermore, the cleavage ratio of oocytes in PVP or PVA group was 37.41% ± 4.17% or 27.71% ± 3.91% and was considerably less than that in the FBS group (64.97% ± 4.69%, P < 0.05). In addition, the cleavage ratio in PVP group was statistically higher than that in PVA group (P < 0.05). In terms of blastocyst development, a significant difference was observed between the synthetic polymer group and the FBS group (24.96% ± 3.62%, P < 0.05). However, the blastocyst ratio in the PVA group (7.51% ± 1.68%) was statistically less than the PVP groups (13.20% ± 4.59%, P < 0.05) and the FBS group (P < 0.05). In conclusion, two potential serum replacements, either PVP or PVA, can support IVM and embryonic development of goat oocytes at the concentration used in this study. But IVM with synthetic polymers supplemented to maturation medium may reduce the cryotolerance of oocytes. Additionally, the supportive function of PVP on embryonic development of vitrified oocytes might be better than that of PVA.