P-118: Stepwise Morphometric Changesduring In Vitro Maturation of Goat Oocytein Relation with Nuclear Remodeling and Developmental Competencee

Background: Successful in vitro maturation (IVM) of oocytes is an important step for production of livestock through assisted reproductive techniques including somatic cell nuclear transfer (SCNT). Obtaining an optimal duration for maturation of oocyte is essential, since over exposure to maturation medium results in oocyte aging, while under exposure leads to production of immature incompetent oocytes. Therefore, this study by assessing stepwise changes of morphometric parameters, nuclear and microtubule remodeling, hopes to obtain the optimal duration for IVM of goat oocytes. Materials and Methods: In experiment 1, cumulus oocyte complexes were fixed at 2 hours intervals from 14 to 32 hours of culture to assess oocyte nuclear maturation and morphometric parameters. The curve for the percentage of oocytes at metaphase II (MII) reached a plateau by 20 hours of IVM culture (64.9% MII) and did not show a significant change thereafter. Also ooplasm diameter, zona pellucida thickness, volume of ooplasm and perivitelline space (PVS) at different interval of in vitro maturation were examined and results show declining trend in diameter and volume of ooplasm and an increase in volume of PVS. But there variations were not significant. In experiment 2, the effects of duration of IVM culture (20, 24, and 30 hours) on the fertilizability of goat oocytes were evaluated. After 20 hours IVM and 20hours of IVF culture, cleavage and blastocyst rates did not differ from other groups (24 and 30 hours) but rate of morula formation significantly increased. Also the quality of blastocysts did not differ between groups. Results: These results suggest that morphometric parameters cannot be applied as prognosis factor in oocyte maturation outcome in IVM program, as no relation were observed between morphometric parameters and nuclear statues. The best organization of microtubules and arrangement of chromosomes on spindles were observed at 20 hours post maturation. Conclusion: Based on this observation, we proposed that 20 hours may be considered as the optimal time for IVM in goat.