Effect of Addition Vitamin C and Zinc Chloride in Vitrification Medium on Viability, in vitro Maturation and Ultrastructure Changes of Vitrified Immature Bovine Oocytes

This study aimed to evaluate the impact of adding vitamin C and zinc chloride to vitrification medium on viability in vitro maturation and ultrastructure changes of vitrified immature Baladi cow oocytes. Compact cumulus oocytes (COCs) (n=1370) were obtained from slaughtered bovine ovaries. Then the morphology of oocytes was examined using a stereomicroscope.  Staining with trypan, the in vitro maturation and ultrastructural changes were studied. The results revealed significant (P<0.05) increase of total and normal survival rate of bovine oocytes vitrified with zinc chloride (90.28 and 81.11%) than in vitamin C media (82.5 and 65.65%) or control medium (74.44 and 54.72%). Recovery rate of abnormal bovine oocytes showed significantly an opposite trend (9.17 vs. 16.94 and 19.72%). Proportion of oocytes with viable cytoplasm and viable cumulus (VOVC) was increased significantly (93.75%, P<0.05) in fresh (control) than in medium supplemented with vitamin C and untreated medium (74.55 and 68.63%), respectively. There were non-significant differences among zinc chloride, control and vitamin C media in oocytes with vaible cytoplasm and unvaiable cumulus (VOUC). Supplementation of the vitrification medium with zinc chloride and vitamin C significantly (P<0.05) improved maturation rates (MII) of recovered cumulus oocyte complexes (COCs) than medium without supplementation. The percentage of ultrastructural alterations in most organelles bovine oocytes significantly (P<0.05) increased in oocytes vitrified without supplementation followed by vitamin C, then zinc chloride medium. Conclusion, supplementation of vitamin C or zinc chloride to the vitrification medium improved survival rate, morphologically and ultrastructural, as well as maturation rate of bovine oocytes