Effects of follicle size and culture duration for in vitro maturation on development of bovine oocytes

摘要

The objectives of this study were to compare different follicle sizes (Large: 6-9 mm and Small: 2-5 mm in diameter) and culture duration for in vitro maturation (IVM) (0, 18, 20, 22, 24 h) on in vitro development of bovine oocytes. We also examined the concentrations of follicular fluid estradiol-17#beta# (E_2) and progesterone (P_4).In Experiment 1, oocytes aspirated from follicles (2-5 mm: small, 6-9 mm: large) were cultured for various periods for IVM (0, 18, 20, 22, 24 h). The oocytes from small follicles were significantly (P<0.05) higher rate of germinal vesicle break-down stage than those from large follicles. The proportion of oocytes at germinal vesicle stage was significantly (P<0.05) lower in the oocytes cultured from small follicles, as compared of those from large follicles. The oocytes from small follicles and cultured for 18 h were significantly (P<0.05) higher rate of prophase stage than those from large follicles. The proportion of oocytes at metaphase II stage was significantly (P<0.05) higher rate of prophase stage than those from large follicles. The proportion of oocytes at metaphase II stage was significantly (P<0.05) higher after 24 h in culture than those after 18 h in culture. There were no significant differences in the nuclear maturation stages between follicle sizes and between maturation periods (20, 22, 24 h).In Experiment 2, E_2 and P_4 concentrations of follicular fluid were measured by enzyme immunoassay. There was no significant difference in P_4 concentration between the follicular fluid collected from large and small follicles (1.7+-0.59 pg/ml and 1.6+-0.83 pg/ml, respectively). E_2 concentration in the follicular fluid from large follicles was significantly (P<0.05) higher than that in the follicular fluid from small follicles (228.3+-67.6 pg/ml and 24.1+-1.8 pg/ml, respectively). The oocytes aspirated from two different sizes of follicles were cultured for 20, 22 or 24 h. The oocytes were then cultured throughout IVF to IVC. The oocytes collected from large follicles and cultured for 20 h were significantly (P<0.05) higher rate of >=2-cell and >=8-cell stages than those from small follicles. There was no significant difference in the developmental rates of oocytes cultured for 22 h and 24 h. The oocytes from large foolicles were significantly (P<0.05) higher rate of >=8-cell stage than those from small follicles, but blastocyst development did not significantly differ in the oocytes from large and small follicles.These results indicate that oocytes from small follicles need to culture more than 20 h for IVM and there were no significant differences in the maturation periods between 20-24 h on development of bovine oocytes after IVF/IVC. The oocytes from large follicles were significantly (P<0.05) higher rate of >=8-cell stage than those from small follicles. However it was not found that the oocytes from large follicles were higher developmental capacity to blastocyst stage than those from small follicles.