L-Histidine Improves Boar Sperm Quality by Alleviating Oxidative Stress During Preservation at 17 °C

Oxidative damage is closely associated with the gradual decline in boar sperm quality during liquid storage at 17 °C. To determine whether L-histidine (L-His) could limit this deterioration, semen was diluted with an extender containing 0, 1, 10, 100, or 1000 μM L-His. Motility and acrosomal integrity were measured throughout storage. On day 7, mitochondrial membrane potential (MMP) and ATP content were determined together with intracellular probe oxidation, membrane lipid oxidation, and Annexin V-FITC/PI staining patterns. The stored sperm were subsequently exposed to capacitating conditions and tested for their ability to bind to oviductal explants. The most favorable responses were observed with 100 μM L-His. Compared with untreated semen, this group retained higher motility and acrosomal integrity and showed higher MMP and ATP content (p < 0.05). It also exhibited less intracellular probe oxidation and membrane lipid oxidation, together with lower proportions of Annexin V-positive and membrane-compromised sperm. Following capacitation induction, sperm stored with 100 μM L-His showed increased tyrosine phosphorylation and higher proportions of capacitated sperm. Their binding index to oviductal explants was also higher than that of the control group. These findings indicate that supplementation with 100 μM L-His can improve the preservation quality of boar sperm during extended liquid storage at 17 °C and maintain functional characteristics of stored sperm, providing new insights into the potential use of L-His as a semen extender supplement for prolonged storage.