Effects of Follicular Fluid and Serum Supplementation on Cumulus Cell Expansion and Nuclear Progression of Guinea Pig Oocytes, Using a Baseline Medium Established with Bovine Oocytes

This study evaluated the effects of serum (egpS) and follicular fluid (egpFF) from estrus guinea pigs as in vitro maturation (IVM) supplements for natural cycle guinea pig oocytes. Two experiments were conducted: the first assessed three IVM media, a commercial medium (CMOM) and two homemade media (HMOM-P and HMOM-S), for oocyte in vitro maturation using 615 bovine oocytes, while the second evaluated the incorporation of 5%, 10%, and 20% egpFF or egpS into IVM media for 1744 guinea pig oocytes. Initially, we optimized the IVM base medium using bovine oocytes to determine the most suitable culture conditions. The results obtained from these experiments served as a critical foundation for subsequent supplementation trials conducted with guinea pig oocytes. The oocytes were cultured in 70 μL drops under controlled atmospheric conditions, and maturation rates were assessed based on cumulus cell expansion and nuclear progression. The HMOM-S medium significantly enhanced cumulus cell expansion (72.5 ± 2.88%) compared with the CMOM medium (57.7 ± 5.33%; p < 0.05). Supplementation with egpFF at 5% (68.8 ± 6.22%), 10% (76.3 ± 5.39%), and 20% (80.9 ± 6.22%) significantly improved both cumulus cell expansion and nuclear progression in high-quality oocytes (types A and B), compared to the control group (43.3 ± 4.82%). Conversely, supplementation with egpS did not have a significant effect on cumulus cell expansion (p > 0.05); however, it notably improved nuclear maturation in low-quality oocytes (type C) at concentrations of 10% and 20% (p < 0.05). This resulted in an overall improvement in maturation outcomes, particularly for oocytes with compromised initial quality. These findings demonstrated that the IVM of guinea pig oocytes using HMOM-S medium was significantly enhanced by the presence of egpFF, whereas egpS supplementation exhibited a less pronounced effect on IVM outcomes.