The effect of serum on in vitro maturation, in vitro fertilization and steroidogenesis of bovine oocytes co-cultured with granulosa cells

ABSTRACT

The influence of fetal calf serum alone (fcs) or associated with proestrous (FCS + PCS), ESTROUS (FCS + ECS) or metaestrous (FCS + MCS) cow serum added to the culture medium and of the steroids produced by co-cultured granulosa cells were evaluated in terms of the in vitro maturation (IVM) and fertilization (IVF) of bovine oocytes. Supplementation of the medium with 9FCS + ECS and FCS + MCS resulted in higher proportions of oocytes that reached metaphase II (96.0 per cent and 93.3 per cent, respectively) and in higher proportion of embryos that reached the four- and eight-cell/morula stages (51.9 per cent and 65.6 per cent, respectively), whereas the supplementation with FCS and FCS + pcs resulted in only 79.2 per cent and 67.5 per cent, respectively, of matured oocytes nd 26.7 per cent and 34.4 per cent, respectively, of cleaved embryos. These findings show that the best IVM and IVF were obtained at lower concentrations of estradiol produced by co-cultured granulosa cells (supplementation with FCS + ECS 10.3 ng/ml and FCS + MCS 2.1 ng/ml), whereas the worst results in IVM and IVF occurred at higher concentrations of estradiol that were obtained with FCS (33.1 ng/ml) and FCS + PCS (19.9 ng/ml) supplementation. These data suggest an inhibitory effect of estradiol on resumption of oocyte meiosis in vitro