Abstract
Immature bovine oocytes aspirated from small follicles (2-5 mm) are not all developmentally competent following maturation and fertilization. It is suspected that the follicles provide the proper signal to the oocyte during late folliculogenesis. To assess the effects of follicular components, steroids, and gonadotropins on subsequent development, it is important to maintain the oocyte in a state of maximum receptivity, at the germinal vesicle (GV) stage. This study evaluates the inhibitory effects of co-culture with hemi-sections follicles on the meiotic resumption and subsequent development of cumulus-enclosed primary oocytes in vitro. One or 2 follicular hemi-sections prepared by careful dissection of follicles (2-5 mm) were co-cultured for 15 h with groups of 10 oocytes in the presence of FSH, estradiol or both. Oocytes were fixed after incubation for 15 h or incubated for an additional 24 h in a conventional maturation medium (FSH-LH and estradiol) or a medium containing progesterone and LH to stimulate meiotic resumption. Co-culture with 1 or 2 hemi-sections resulted in 37 to 76% GV rates. Inhibition of spontaneous oocyte maturation due to the co-culture was influenced by neither estradiol nor FSH, and 57 to 97% of oocytes reached the metaphase II stage in the subsequent 24 h culture, but at a lower rate with estradiol alone. Successful embryonic development of these oocytes after successive treatments of in vitro maturation (24 h), fertilization (10 h) and culturing with oviduct cells (96 h) indicates that viability is maintained after co-incubation with hemi-sections.
