Abstract: Experiments were conducted to study the effects of follicle size and bovine follicular fluid (BFF) on developmental competence of bovine oocytes derived from abattoir ovaries following in vitro maturation, fertilization and culture. In experiment 1, bovine COCs (cumulus oocyte complex) derived from follicle of different sizes were allocated to four treatments according to follicles size:＞8 mm; 2-8 mm; preantral follicle (PF); and mix above COCs together (mix). The result showed that follicle size directly affected the development of oocytes and mixing all sizes of follicle oocytes together could stimulate development of immature oocytes from PF. In experiment 2, 10% of bovine follicular fluid (BFF) derived from competent follicles (＞8 mm ), small follicles(2-8 mm ) or all sizes of follicles (mix) were supplemented to the maturation medium. Following in vitro maturation, feitilization and culture, more COCs in three treatments reached cleavage and blastocyst than no BFF control group (P<0.05). However,10% of BFF from competent follicles made the oocytes and embryos sticking together and may easily cause some of them lost. In experiment 3, different concentrations (10%, 20% and 40%) of BFF from all follicles (＞2 mm) were supplemented to the maturation medium. The results showed that different concentrations of BFF could support in vitro maturation of COCs and subsequent development capacity, however, 20% and 40% of BFF could seriously cause oocytes and embryos adhered together. Therefore adding 10% of mixed BFF in maturation medium is the best choice.

Key words: Bovine, Oocyte, Follicle, Follicle fluid, in vitro fertilization