Influence of foetal bovine serum on in vitro maturation of sheep oocytes

Oocyte maturation is a pivotal step in achieving successful in vitro embryo production in livestock. Among the various factors influencing in vitro maturation (IVM), the choice of protein supplement plays a crucial role in determining both the maturation rate of oocytes and their subsequent embryonic development following in vitro fertilization (IVF). This study was conducted to evaluate the effect of varying concentrations of fetal bovine serum (FBS) on the in vitro maturation of sheep oocytes. Ovaries collected from mature, non-pregnant slaughtered sheep were washed and cumulus oocytes complexes (COCs) were aspirated from surface follicles (2–6 mm diam.) of ovaries. Sheep oocytes having more than 5 layers of cumulus cells and granular homogenous ooplasm were cultured in culture media with 5%, 10% and 15% FBS and FSH (10 µg/ml) in CO2 incubator (5% CO2 in air, 90–95% relative humidity). The degree of cumulus expansion was assessed after 24 hr of in vitro maturation. Oocytes with expanded cumulus cell mass to at least 2 diameters away from the zona pellucida were considered as cumulus expanded. The maturation of oocytes was further evaluated by identifying the first polar body in the perivitelline space after denuding them. The addition of protein supplement in the form of FBS (5%, 10% and 15%) improved the oocyte maturation rate. The maturation rate was significantly (P<0.05) higher in oocytes exposed to 10% FBS (87.5±2.5%) as compared to those exposed to 15% FBS (52.5±2.5%). Cumulous expansion of oocyte was maximum in presence of 10% FBS as compared to other doses tested. It can be concluded that 10% FBS increased the percentage of oocytes with complete cumulous cells expansion as compared to 5% and 15% FBS.