Effect of Adding Different Levels of Folic Acid to the Culture Medium on Developmental Competence of Bovine Oocytes

This study aimed to investigate the effects of adding different levels of folic acid (FoA) in culture medium on bovine embryo developmental competence, reactive oxygen species (ROS) content, and expression of DNA methylation genes. In this study, different levels of FoA including 0, 10, 100, and 1000 ng/mL were added to maturation medium, and then the matured oocytes were subjected to in vitro fertilization (IVF) and in vitro culture (IVC). To determine the intracellular ROS activity in oocytes, a 20, 70-dichlorofluorescein light assay was used. RNA was extracted from ovaries, denuded mature oocytes and blastocysts using a commercial kit to determine relative expression of DNA methyltransferase 1 (Dnmt1), Dnmt3a, and Dnmt3b. The addition of FoA decreased (P<0.05) oocyte ROS content in all the treated groups compared to the control group; meanwhile, the lowest level was noted in FoA100 group (P<0.05). The fertilization rate was improved (P<0.05) in FoA10 and FoA100 compared to the control group. Transcript abundance of Dnmt1 in the matured oocyte was increased in FoA10 and FoA100 compared to the control (P<0.05), but the highest level was noted in FoA100. Folic acid enhanced the expression of Dnmt3a and decreased that of Dnmt3b in bovine oocytes (P<0.05). Transcript abundance of Dnmt3a and Dnmt3b in the FoA100 blasto-cysts indicated an increase and decrease, respectively relative to the control group (P<0.05). These findings showed that the addition of 100 ng/mL of FoA to the oocyte maturation culture medium has a beneficial effect on the fertilization rate and developmental competence of produced zygote.