This study aimed to determine whether adding niacin to the oocyte maturation medium could enhance fertilization rate, mitochondrial distribution, and the expression of mitochondrial function–related genes in fresh and vitrified bovine oocytes. In Experiment 1, cumulus–oocyte complexes (COCs) were allocated into two groups for in vitro maturation: a control group and niacin‐supplemented (niacin group) oocytes. In Experiment 2, COCs were matured under the same conditions as in Experiment 1 and then vitrified, forming two additional groups: control vitrified (CV) and niacin‐supplemented vitrified (NV) groups. Fertilization rate, mitochondrial distribution, and gene expression were examined in the matured oocytes in both experiments. In Experiment 1, fertilization rate and gene expression were analyzed using a paired t ‐test. In Experiment 2, fertilization rate and gene expression were analyzed by ANOVA with LSD post hoc test. Mitochondrial distribution patterns were assessed by Pearson’s chi‐square test in both experiments. In Experiment 1, niacin supplementation significantly improved fertilization rate and upregulated TFAM , POLG , and NRF1 expression compared with the control group ( p ≤ 0.05). In Experiment 2, although vitrification reduced fertilization rate overall, NV oocytes showed a tendency toward higher fertilization rate compared with the CV group ( p = 0.08). Mitochondrial distribution in the CV group shifted toward a peripheral pattern, whereas niacin supplementation resulted in a more normal distribution. Vitrification decreased the expression of COX1 , POLG , and NRF1 ( p ≤ 0.05) in the oocytes, but NRF1 and POLG levels in the NV group were significantly higher than those in the CV group ( p ≤ 0.05). In conclusion, niacin supplementation during in vitro maturation of bovine oocytes enhances fertilization competence by supporting mitochondrial distribution and mitochondrial gene expression, particularly under vitrification stress.
Azari et al. (Thu,) studied this question.