Abstract
The objective of this study was to clarify the effect of ovarian status and follicular size on morphological normality and maturational ability of cat oocytes. Ovarian status was classified into inactive, follicular, luteal and pre-pubertal, and follicles were classified into three groups according to their diameter (400–800, 800–1,200 and 1,200–2,000 μm). In each ovarian status, number of follicles decreased but percentage of morphologically normal oocytes increased with the growth of follicles (P<0.05). Only single follicle with 1,200–2,000 μm in diameter was observed in two of five pre-pubertal cats. In follicles with 800–1,200 μm in diameter, percentage of normal oocytes and maturation rate were higher in pre-pubertal cats than those in mature cats (P<0.05). The diameter of oocytes tended to increase with the growth of follicles. After oocytes were cultured individually in droplets of maturation medium, maturation rate of oocytes increased with the growth of follicles in each ovarian status (P<0.05). In conclusion, oocytes collected from larger follicles possess higher maturational ability in vitro in sexually mature cats. In pre-pubertal cats, higher maturation rate can be obtained from oocytes derived from small follicles when compared to mature cats.
