Dose-Dependent Effects of L-Serine Supplementation on Boar Sperm Quality During Chilled and Cryopreserved Storage

Boar sperm are highly sensitive to oxidative and cold-induced stress during storage, which compromises their functional integrity. This study evaluated the dose-dependent effects of L-serine, an amino acid involved in glutathione synthesis and membrane stabilization, on boar sperm quality under chilled (17 °C) and cryopreserved conditions. Ejaculates from fertile boars were extended with Modena-based media supplemented with 0, 1, 3, 5, and 7 mM L-serine. Sperm quality parameters, including motility, viability, mitochondrial activity, acrosome integrity, lipid peroxidation (measured by malondialdehyde (MDA)), and antioxidant enzyme activity, were assessed over five days for chilled semen and post-thaw for cryopreserved samples. L-serine at 3 mM was most effective in maintaining chilled semen quality, as evidenced by superior motility, viability, and acrosome integrity by Day 5, accompanied by lower MDA levels and increased glutathione peroxidase and catalase activities. In contrast, 1 mM was optimal for cryopreserved semen, improving post-thaw motility, mitochondrial activity, and antioxidant defense while reducing lipid peroxidation. Higher concentrations (≥5 mM) consistently impaired sperm function, likely due to osmotic stress or redox imbalance. These findings indicate that L-serine enhances boar sperm preservation in a concentration- and method-specific manner, with 3 mM supplementation most effective for chilled storage, and 1 mM for cryopreservation. This study supports the inclusion of amino acid antioxidants in extender formulations to improve semen preservation in swine artificial insemination systems.