Abstract
The aim of the present experiment was to investigate the effect of follicular size on oocyte cumulus-expansion, in vitro fertilization and subsequent developmental competence. After maturation culture, the rates of porcine oocytes with expanded cumulus derived from antral follicles ≥5 mm, 4-4.9 mm, 3-3.9 mm and 2-2.9 mm in diameter were 90.5%, 89.7%, 85.4% and 67.4%, respectively. After in vitro fertilization, the developmental competence of oocytes dependently increased with follicular size. Higher cleavage rates and higher proportions of 3-4-cell embryos were obtained from ≥4 mm follicles compared to 2-2.9 mm follicles (P<0.05). Although the proportions of 6-8-cell and 12-16-cell embryos obtained from ≥5 mm, 4-4.9 mm, 3-3.9 mm and 2-2.9 mm follicles showed no significant differences, embryos obtained from 2-2.9 mm follicles showed a complete failure to develop beyond the 8-cell stage, embryos obtained from 3-3.9 mm follicles failed to develop beyond the 16-cell stage and none of embryos developed beyond the early stage of morula. The percentages of expanded cumulus-oocyte complexes (COCs) and 2-cell cleavage rates of oocytes derived from 2-2.9 mm follicles were not significantly different when the oocytes were matured for 36 h , 42 h and 48 h in vitro. The exposure to 5% or 15% porcine follicular fluid (PFF) from the large follicles during in vitro maturation (IVM) had no significant effect on the cleavage and subsequent developmental rates of porcine oocytes compared to PFF from small follicles.
