Effects of culture time, ovarian activity, cumulus cells and sera on the nuclear and cytoplasmic maturation of pig oocytes in vitro

Abstract

Pig cumulus-oocyte complexes (COC) were used in this study to assess the effect of length of culture, ovarian activity, cumulus cells and sera on maturation and fertilization in vitro. In Experiment 1, the incidence of nuclear maturation increased ( P<0.01) from 24 to 48 h of culture and the ability for male pronucleus (MPN) formation peak at 42 h (86.6%). The penetrability of immature COC and those at the metaphase 2 (M2) stage appeared to be not influenced by the stage of meiosis (75.3–89.3%). In Experiment 2, no significant difference in the nuclear maturation (84.8–88.0%) and penetration (82.1–92.0%) rates of COC collected from ovaries with or without corpora lutea (CL) or corpora albicans (CA) was observed, though MPN formation differed ( P<0.05) between O 1 (82.6%) and O 3 (61.5%) oocytes. In Experiment 3, significant differences ( P<0.01) on the nuclear maturation and MPN formation of oocytes cultured with cumulus cells versus those without or lacking cumulus cells was observed. It shows that the presence of cumulus cells is important in supporting maturation in vitro. In Experiment 4, serum supplementation of the medium improved the rate at which COC reached the M2 stage ( P<0.05) and formed MPN except at the 5% level when using fetal bovine serum (FBS) and calf serum (CS). The use of porcine serum (PS) consistently supported the maturation of COC. Serum supplementation is thus necessary for maturation in vitro and the concentration and type of serum to be used is important.