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This study was carried out to investigate the factors affecting maturation in vitro of follicular oocytes in Korean Native Cattle. The bovine ovaries were obtained at a slaughter house and the follicular oocytes were recovered by aspirating the follicular fluid from the visible follicles of 3~6mm. The bovine oocytes were matured in vitro in TCM-199 containing FCS and hormones. The effects of TCM-199 salt type, number of oocytes per drop, incubation time and co-culture with granulosa cells on maturation of oocytes, were investigated. The results obtained are summarized as follows. 1. The maturation rates of follicular oocytes cultured for 22, 25 and 28 hours in Hank’s TCM-199 or Earle’s TCM-199 were 59.3, 59.6, 80% and 80.0, 90.0, 93.7%, respectively. The maturation rate of follicular oocytes in Earle’s TCM-199 was faster and higher than in Hank’s TCM-199(P<0.05). 2. The maturation rates of oocytes were 54.5, 62.5 and 62.0% when cultured the oocytes number 10, 20 and 40 per 200{mu}ell drop for 18 hours. 3. The maturation of follicular oocytes in the Korean Native Cattle was induced at 14 hours culture, by giving the maturation rate of 90.0% after 20 hours. 4. The maturation rates were 63.3% and 66.7%, respectigely when the oocytes were co-cultured with granulosa cells from medium-size follicles used immediately after recovery in the presence or absence of hormones added(0.02AU/ml FSH, 10mutextrm{g}/ml LH and 1mutextrm{g}/ml estradiol 17-beta). When the oocytes were co-cultured with granulosa cells from medium-size follicles cultured for 3 days, the maturation rates were 20.8% and 76.2%, respectively(P<0.05). 5. The maturation rate were 88.0% and 70.0%, respectively when the oocytes were co-cultured with granulosa cells from large-size follicles used immediately after recovery in the presence or absence of hormones added(0.02AU/ml FSH, 10mutextrm{g}/ml LH and 1mutextrm{g}/ml estradiol 17-beta)(P<0.05). When the hormones added(0.02AU/ml FSH, 10mutextrm{g}/ml LH and 1mutextrm{g}/ml estradiol 17-beta)(P<0.05). When the oocytes were co-cultred with granulosa cells from large-size follicles cultured for 3 days, the maturation rates were 41.2% and 73.3%, respectively(P<0.05).
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