Abstract:

The aim of the study was to investigate the effect of follicle size and follicle stimulating hormone (FSH) concentration on nuclear maturation of bovine oocytes in vitro. Follicles on bovine ovary were classified into 3 groups according to the diameter; small (<3 mm), medium (3–8 mm) and large (9–12 mm). Oocytes were aspirated from follicles with different size and matured in tissue culture medium (TCM–199) supplemented with 10% FCS and various concentrations of FSH (0.5, 1.0 or 10 and μg/ml) for 22 hours filled with approximately 95% humidified and 5% CO2 in air at 38.5 °C. At the end of culture period, nuclear maturation (at metaphase II; MII) of oocytes were determined by Bisbenzimide (Hoechst 33258) DNA staining under fluorescent microscope. In the present study, effect of follicle size on nuclear maturation of bovine oocytes were determined and the percentage of oocytes reached to M II stage was significantly lower in oocytes obtained small follicle than those of medium and large follicles. Supplementation of 10.0 μg/ml FSH into maturation media increased percentage of nuclear maturation compare to 0.5 and 1.0 μg/ml. Additionally, improving effect of high FSH concentration on nuclear maturation were more observed in oocytes obtained small follicles. The results of present study showed that oocytes from follicles with 3–8 mm diameters exhibited a more successful maturation, but oocytes obtained small follicles exhibited more maturation as a ratio under high FSH concentration.

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