Developmental competence of ovine oocyte following vitrification: effect of oocyte developmental stage, cumulus cells, cytoskeleton stabiliser, FBS concentration, and equilibration time.

The aim of the present study was to examine the effects of fetal bovine serum (FBS) concentration, equilibration time, and oocyte pre-treatment with cytochalasin B (CCB) on subsequent development of vitrified-warmed ovine immature (GVCOCs) and matured (MII) oocytes with (MIICOCs) or without cumulus cells (MIIDOs). In Experiment 1, the effects of FBS concentrations (10 and 20%) during the vitrification-warming procedure were examined. Survival rates after warming were not different between GVCOCs, MIICOCs and MIIDOs oocytes. After in vitro fertilization, rate of cleaved embryos in MIICOCs group at the presence of 20%FBS was higher than MIIDOs and GVCOCs groups. In Experiment 2, the effects of equilibration times (5, 7, and 10 min) were examined. There was no difference in survival rate of vitrified-warmed oocytes equilibrated at different times. Although, the rate of cleavage in MIICOCs and MIIDOs oocytes equilibrated for 10 and 7 min, respectively, was higher than 5 min equilibrated MIIDOs and 7 and 10 min equilibrated GVCOCs oocytes. In Experiment 3, the effects of oocyte pre-treatment with CCB were examined. Despite the insignificant difference in survival rate of vitrified-warmed ovine immature and matured oocytes, the rates of cleavage in CCB pretreated groups were significantly lower than untreated groups. Moreover, the blastocysts were only derived from those cumulus enclosed vitrified-warmed germinal vesicle (GV) and MII oocytes that had been exposed to 10% FBS in the absence of CCB. In conclusion, the presence of cumulus cells, 10% FBS, and the omission of CCB were beneficial for post-warming development of vitrified ovine oocytes.