Effect of Various Concentrations of Glucose on Bovine Cumulus-Oocyte Complexes Maturation, Fertilization and Early Embryonic Development in Vitro

Different energy substrates and nutrients can greatly influence oocyte nuclear and cytoplasmic maturation. Effect of glucose on in-vitro oocyte maturation and subsequent early embryonic development is controversial. The objective of the present study was to verify the effect of various concentrations of glucose on cumulus-oocyte complexes maturation, fertilization and early embryonic development using a bovine model. Ovaries were collected from the local abattoir and brought into laboratory. Cumulus-oocyte complexes (n=1170) were aspirated from follicles, randomly divided into 4 groups (3 treatment/experimental & 1 control), and cultured in an organ culture dish containing 1 ml maturation medium, in treatment groups, chemically defined medium, supplemented with 1.0, 1.5 or 3.0 mg/ml D-glucose respectively, at 38.5 degrees on the Celsius scales in an atmosphere of 5% CO2 and 95% air with high humidity for 24 hours. Following maturation, 394 oocytes were fixed randomly for 24h, for maturation rates; and 776 oocytes were inseminated with frozen-thawed bull semen for fertilization rates and early embryonic development, 387 oocytes (presumptive zygotes) fixed randomly for fertilization rates, and 389 oocytes (presumptive zygotes) were cultured for development with similar medium to blastocyst stage (day 8). The samples were examined by streomicroscope and the results were analysed by X2 test. The oocytes maturation rates were higher (P<0.001) in the medium contained glucose compared to the control group (82%, 79% and 80% vs. 55% respectively). Although fertilization rates of oocytes were not different among groups, (57%, 54% and 50% vs. 49% respectively), the rates of blastocyst formation in the treatment group were significantly higher (p<0.01) than the control (30%, 33% and 32% vs.14%). These results confirm that the presence of glucose, in the maturation medium, is important for oocyte maturation and the subsequent embryonic development.