The Influence of L-Serine on Sperm Quality, Malondialdehyde, and Antioxidant Enzyme Activity After Cryopreservation in Bull Semen.

Bull semen cryopreservation is essential for preserving valuable genetics and supporting cattle breeding programs; however, freeze-thaw stress compromises post-thaw sperm quality through oxidative damage and membrane injury. This study evaluated the effects of L-serine supplementation on post-thaw semen quality, susceptibility to induced lipid peroxidation, and antioxidant enzyme activity in bull semen. Semen collected from four Brahman bulls was cryopreserved in a Tris-based extender supplemented with 0, 2, 4, or 6 mM L-serine. Post-thaw total motility, progressive motility, viability, plasma membrane integrity, MDA concentration, and the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) were assessed. Supplementation with 2 and 4 mM L-serine resulted in higher total motility and progressive motility, and greater plasma membrane integrity than the control and 6 mM treatments (p < 0.05), while viability was higher with 4 mM than with the control and 6 mM treatments (p < 0.05). MDA concentration following induced lipid peroxidation was lower in all L-serine-supplemented treatments than in the control (p < 0.05). SOD activity was higher with 2 mM than with the control and 6 mM treatments (p < 0.05), whereas GPx activity was highest with 2 mM, followed by 4 and 6 mM, with the lowest activity in the control (p < 0.05). CAT activity was unaffected by treatment (p = 0.1192). Overall, supplementation with 2-4 mM L-serine improved selected post-thaw sperm quality parameters and was associated with reduced susceptibility to induced lipid peroxidation and changes in apparent extracellular antioxidant enzyme activities. These findings support the potential of L-serine as a functional additive to improve bull semen cryopreservation.