The recovery of follicular oocytes from the rabbit ovary during prepubertal age and in vitro maturation of their oocytes.

Abstract

The recovery of oocytes from minced ovarian tissues was examined as well as the ability of their oocytes to mature to Metaphase II in immature rabbits (2-, 3-and 4-month-old), treated with PMSG or not. The number of visible large follicles (over 1 mm in diameter) on the ovary, as well as ovarian weight, increased with advancing age and the increase was remarkable in 3-and 4-month-old PMSG-treated does. Blood follicle formation was marked only in PMSG-treated does 4-month-old. In histology, many antral follicles were grown in 3-and 4-month-old does; especially the number of healthy follicles >700μm in diameter was markedly increased in 3-month-old PMSG-treated does. Ratios of the number of healthy antral follicles >700μm in diameter were still higher in the PMSG-treated does than in non-treated does. In oocytes recovered by mincing ovaries using a pair of razors, only oocytes surrounded by a thick layer of cumulus cells (Type I oocyte) were selected and cultured for in vitro maturation. The number of Type I oocytes was increased by PMSG treatment at each age; the number in 3-month-old does was the highest (3 times that in non-treated does). Ratios of Type I oocytes which emitted the first polar body in in vitro culture increased with advancing age up to 4 months, though the ratios remained at lower levels than in adult does. There were no differences in the maturation ratios between PMSG-treated and non-treated groups. These results show that oocytes to undergo in vitro maturation are obtainable from the ovary in immature rabbits, especially in 3-month-old PMSG-treated does.