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ABSTRACT High‐yielding dairy cows are susceptible to mammary gland oxidative stress due to prolonged intensive lactation, leading to redox imbalance. Our previous research linked this condition to reduced lactation lifespan. This study compared mammary glands from high‐yielding and normal‐yielding cows, revealing significant oxidative stress in high‐yielders, evidenced by decreased FRAP and SOD levels, and increased GSH, MDA, and H 2 O 2 . Mitochondrial function was disrupted, with impaired dynamics. Metabolomic analysis identified a significant downregulation of Myo‐inositol (MI) in high‐yielding cows. Using H 2 O 2 ‐stimulated bovine mammary epithelial cells (MAC‐T) as an in vitro oxidative stress model, we confirmed MI depletion, mitochondrial fission, cellular senescence, and decreased Sirt5 protein. MI supplementation upregulated mitochondrial fusion proteins (OPA1, MFN1, and MFN2) and downregulated fission proteins (FIS1 and Drp1), alleviating oxidative stress. Mechanistic studies revealed that Sirt5 knockdown reduced Nrf2 expression, and inhibiting Nrf2 with retinoic acid (RA) abolished MI's protective effects. This demonstrates that MI alleviates oxidative stress in MAC‐T cells primarily by activating the Sirt5/Nrf2 pathway to promote mitochondrial fusion. These findings elucidate a novel mechanism for MI's antioxidant role in the dairy cow mammary gland.
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