Effect of the in vitro maturation medium on equine oocytes: Comparison of follicular fluid and oestrous mare serum

The present study evaluated the effect of supplementing the medium used to mature equine oocytes in vitro with oestrous mare serum (EMS) or horse follicular fluid (HFF). To this end, 144 ovaries were obtained from mares aged 16-21 months and transported to the laboratory in Dulbecco's phosphate buffered saline (D-PBS) at 30°C. Oocytes were harvested from the ovaries by slicing, and then selected for in vitro maturation (IVM) according to the number of cumulus cell layers and the characteristics of the cytoplasm. The selected oocytes were washed three times in TCM199 medium plus HEPES (TCM-199H) or in the same medium plus glutamine (TCM-199G), then matured in vitro in six study groups established according to the in vitro maturation (IVM) treatment to see possible interactions between HEPES and glutamine on other supplements: Ten percent EMS was added to two of these media (TCM-199H+EMS and TCM-199G+EMS) and 10% HFF was added to the media in two other groups (TCM-199H+HFF and TCM-199G+HFF). IVM was performed at 38.5°C for 40 h in a controlled atmosphere (5% CO2, 95% relative humidity). The findings indicate that the presence of EMS or HFF in the TCM-199H medium gives rise to the best results in terms of the proportions of oocytes reaching maturity (37.7% and 36.8%, respectively). The values obtained with EMS and HFF were statistically similar to each other but differed from the other treatments. The media containing glutamine led to the highest proportions of degenerated oocytes