Maturation in Vitro and Subsequent Penetrability of Bovine Follicular Oocytes

To investigate optimum conditions for the resumption of meiosis in vitro, 450 bovine follicular oocytes were incubated for 0 to 36 hr in Ham's medium F-10 with 10% fetal calf serum. At recovery one oocyte was binucleate, 4% were degenerative and 8% had undergone germinal vesicle breakdown. After 28 hr in culture, 60% of the oocytes reached metaphase II and further incubation did not increase the proportion that matured. No significant difference was observed in the proportion of oocytes that matured in vitro from follicles flushed either 1 hr (78%) or 2 hr (72%) after the death of the donors. Oocytes matured in media with pH's ranging from 6.70 to 7.59. The highest proportion (69%) reached metaphase II in media at pH 7.00 to 7.29. Attempts to obtain sperm penetration of bovine oocytes incubated in vitro were successful in the pig oviduct (17%) but not in the sheep oviduct. In conclusion, under conditions which yielded a large proportion of metaphase II oocytes, these oocytes were able to be penetrated and form pronuclei.