Abstract: To investigate the effect of FSH on nuclear maturation of sheep oocyte matured in vitro, the COC were cultured in IVM medium for 24 h, and were divided into 4 tgroups according to four different durations. Then, the rates of GVBD and exclusion of polar body Ⅰ(Pb I)were also analyzed respectively. Results: there were no significant differences in rate of GVBD among those three groups treated with FSH in the first 4 h or 8 h,but there were significant differences in rate of exclusion of Pb I of oocytes among the groups added with FSH from 4 h to 24 h,or 8 h to 24 h. Conclusion: FSH does not promote the meiotic division of ovine oocytes matured in vitro during the first 8 h, but it may play an important role during the period between the stage of GVBD and exclusion of PbⅠ.

Key words: sheep; oocyte; FSH; nuclear maturation; in vitro maturation