Liquid storage of boar semen: Current approaches to reducing sperm damage using antioxidants and nanotechnology.

Due to the high sensitivity of boar sperm to cryodamage, AI with liquid-stored semen is a widely adopted practice in the pig industry. Despite its widespread use, liquid storage at low temperatures adversely affects semen quality, leading to a progressive decline in reproductive performance over time. This deterioration is primarily attributed to cold shock and oxidative stress (OS), which results from the excessive generation of ROS that overwhelms the inherent antioxidant defenses of seminal plasma. Consequently, sperm motility, viability, plasma membrane and acrosome integrity, mitochondrial function, and DNA stability are compromised, which ultimately triggers apoptosis. As a result, fertility rates and litter sizes following AI with liquid-stored semen decline significantly, particularly after 3 days of preservation. This review provides an in-depth exploration of the fundamentals of liquid-state semen storage and elucidates the underlying mechanisms responsible for sperm damage during this process. It also further discusses various factors influencing the quality of liquid-stored boar semen and presents effective mitigation strategies with a focus on the incorporation of additives, antioxidants, and macromolecules into semen extenders. Lastly, this review summarizes recent advancements in the application of nanotechnology to enhance the liquid-state storage of boar semen and explores emerging strategies aimed at improving the quality of stored germplasm.