Abstract: Bovine small preantral follicles whose diameter <100 μm (61-70 μm in average) were chosen to culture in vitro. EGF, bFGF and hydrocortione were added to α-MEM medium containing ITS, Sodium Pyruvate, and L-Glutamine, hypoxanthine, serum, FSH, LH, E2. The first experiment result showed that the follicles were cultured for 7 days in vitro when the concentration of FSH, LH, E2 were 0.25 μg·ml-1, 5 iu·ml-1, 0.5 μg·ml-1. The development of the follicles when using both EGF and bFGF was better than with EGF or bFGF individually. When the dose of bFGF（25 ng or 50 ng）was kept invariable, the development of the follicles would be inhibited with the increase of the concentration of EGF . If the dose of bFGF was increased, there would be a good development. The second experiment: the concentrations of FSH, LH and E2 were adjusted into 4 μg·ml-1, 10 iu·ml-1, 0.1 μg·ml-1 and hydrocortione (40 ng·ml-1) was added to α-MEM medium. After being cultured for 13 days in vitro, the developmental rates and the average increasement diameter of follicles in both the test group 3 (EGF 25 ng ) and the test group 4 (EGF 25 ng＋bFGF 50 ng) were significantly better than test group 1 (without EGF, bFGF, hydrocortione ) and test group 2 (only added with hydrocortisone). At the 20 day in vitro culture, in both the test group 3 and the test group 4, the ratio of development follicles were 15.79% and 25.58%, and the maximum increase diameter of follicles were 300 μm and 320 μm, and small antrum of follicles came into being (the rates of antrum formation were 7.69 % and 17.65 %, respectively). While in the test group 1 and test group 2, the developmental rate of the follicles was 0. The results showed that when the follicles were cultured in vitro, the variety of culture system had an important influence on the development of preantral follicles, and the components of medium influenced each other.

Key words: Bovine, Small preantral follicles, in vitro development