Abstract：The mature oocyte cytoplasm have a role in the reprogramming of donor cells, maturation of oocytes become the key factors in the process of nuclear transplantation. In order to study the effect of the removal of cumulus cells around germinal vesicle breakdown(GVBD) on porcine(Sus scrofa) oocyte in vitro maturation, porcine cumulus - oocyte complexes (COCs) were cultured in vitro and got samples per 5 h. Chromosomal morphological changes of porcine oocyte in vitro maturation were examined by aceto-orcein staining technique, and established the timetable of the oocytes chromosome developmental process. Then the cumulus cells were carried off from COCs in 21, 27 and 42 h, respectively. The effects of cumulus cells on oocyte maturation were investigated by counting the number of excreted polar body. From 2~17 h, most of the oocytes were in GV stage (88.30%~52.38%); 22 h, most of the oocytes were in germinal vesical breakdown~premetaphaseⅠ(GVBD~pre-MⅠ)stage(63.25%); 27 h, most of the oocytes in metaphaseⅠ(MⅠ)stage(42.25%); Until culturied for 32 h, the majority oocytes stayed in anaphaseⅠ(AⅠ)(29.90%); 37 h, telophaseⅠ(TⅠ) oocytes were the most (40%); And by 42 h, most of the oocytes reached metaphaseⅡ(MⅡ)stage (72.81%). We carried off cumulus cells at 21, 27 and 44 h and set these oocytes as 3 groups. The result showed that the maturation rate of 21 h group was 25.56%, lower than that of 27 h group, which reached 34.33%, the 42 h group was the highest that reached 84.33%. These results illustrate the importance of cumulus cells on oocyte maturation in vitro oocyte maturation. This study is conducive to further exploring and analyzing the methods of porcine oocytes matured in vitro, improving the culture system for enhanced maturation rate of porcine oocytes in vitro, and lay the foundation for the quality of embryos cultured in vitro.
