Abstract：To improve the utilization of goat oocytes and reduce the decline in oocytes quality caused by aging, the senescence of goat(Capra hircus) oocytes cultured in vitro were studied by comet assay. The results showed that, with the prolonged culture time, especially more than 24 h, the first polar body(PBⅠ) degenerated significantly and the DNA damage increased gradually. These results suggested that apoptosis increased seriously during oocytes culture in vitro. Before 24 h of culture, the percentage of oocytes with PBⅠ increased visibly with the extended culture(20 h, (45.74±2.67)%; 22 h, (66.11±1.12)%). All the mean length of comet tail was less than 100 μm, however, among oocytes with PBⅠ, the percentage of oocytes with comet tail length distributed in 0~50 μm region (20 h, (77.27±2.27)%; 22 h, (40.12±1.55)%) was less than oocytes without PBⅠ(20 h, (83.86±1.34)%; 22 h, (51.39±8.45)%). At 24 h of culture, oocytes with PBⅠ increased to the peak rate(80.19±2.07)%. And there was no difference in the mean comet tail length for both of oocytes with PBⅠor not ((96.08±4.52) μm vs (95.25±9.28) μm). Moreover, the distribution of mean comet tail length was major in 50~100 μm((45.71±0.50)%) and 100~150 μm ((35.45±2.92)%) for oocytes with PBⅠ, while 0~50 μm ((30.92±4.02)%) and 50~100 μm ((33.02±3.23)%) were the major distribution for oocytes without PBⅠ. When the culture time extended to 26 h later, the rate of oocytes with PBⅠ decreased dramatically (26 h, (72.01±2.88)%; 28 h, (59.77±3.59)%). And the mean comet tail length increased continuely for both of oocytes with PBⅠor not, and the percentage of oocytes with more than 150 μm comet tail length increased rapidly. At 30 h of culture, only (46.34±2.07)% of PBⅠ could be observed in oocytes, and the mean comet tail length was (180.11±10.33) μm, (58.33±4.81)% of them with a more than 150 μm comet tail; but for oocytes without PBⅠ, the mean comet tail length was (270±17.72) μm, and (80.95±2.38)% of them with a more than 150 μm comet tail. This study showed that goat oocytes matured after in vitro muturation became increasingly aged along with the extended culture time, and the proportion of aging oocytes increased dramatically when cultured more than 24 h. Through this study, we can get a further more understanding on the mechanism of oocyte aging. It contributed to improve the oocyte quality by reducing the oocyte aging.
