Nicotinamide mononucleotide (NMN), a key precursor of nicotinamide adenine dinucleotide (NAD⁺), plays a central role in cellular energy metabolism. This study investigated the effect of NMN supplementation on boar sperm quality during liquid storage. Semen samples diluted with Modena extender containing 0 to 80 μM NMN were stored at 17 °C for 7 days. Results demonstrate that supplementation with 20 μM NMN significantly improved sperm motility, acrosome integrity, and mitochondrial activity compared with the control group, accompanied by markedly elevated intracellular NAD⁺ and ATP level (p < 0.05). Also, Western blot analysis confirmed the presence of nicotinamide mononucleotide adenylyltransferase 3 (NMNAT3) in boar sperm. Furthermore, sperm treated with 20 μM NMN exhibited a higher level of protein tyrosine phosphorylation and an increased capacitation rate following storage. Tissue explant assays further revealed a significant increase in the number of sperm attached to oviductal epithelial fragments, indicating enhanced sperm–oviduct interactions. The present findings demonstrate that 20 μM NMN supplementation effectively preserves the metabolic activity and functional competence of boar sperm during liquid storage. It provides a promising strategy for improving boar semen preservation.

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.