Succinic acid improves boar semen quality by reducing ROS stress during liquid preservation

Boar sperm are highly susceptible to oxidative stress during in vitro storage, and the inclusion of antioxidants in semen extenders has become an essential strategy to mitigate oxidative damage. This study evaluated the effects of succinic acid (SA) supplementation on boar semen quality and reproductive performance. In Experiment 1, boar semen was diluted in Modena extender supplemented with 1.5, 3.0, or 4.5 mM SA and stored at 17 °C. The addition of 3.0 mM SA significantly improved sperm motility and the proportion of viable sperm with an intact acrosome (p < 0.05). Notably, it enhanced mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) content, glutathione (GSH) concentration, and glutathione peroxidase (GPx) activity, while markedly reducing lipid peroxidation (LPO), malondialdehyde (MDA) levels, and mitochondrial reactive oxygen species (ROS) production (p < 0.05). In Experiment 2, oxidative stress was induced using 100 μmol/L hydrogen peroxide (H₂O₂) to further assess the cytoprotective effect of SA. Supplementation with 3.0 mM SA effectively counteracted H₂O₂-induced reductions in sperm motility and acrosome integrity in viable sperm and restored MMP, ATP content, GSH levels, and GPx activity (p < 0.05), and significantly decreased ROS and MDA levels (p < 0.05). In Experiment 3, boar semen stored for five days was used for artificial insemination to determine the impact of SA supplementation on fertility outcomes. Inclusion of SA in the extender resulted in a significant increase in both the total number of piglets born and the number of live piglets born per litter (p < 0.05). Taken together, these results demonstrate that supplementation of boar semen extenders with 3.0 mM SA provides robust protection against oxidative stress, preserves mitochondrial function, and improves overall sperm quality during storage at 17 °C, and importantly, these cellular benefits translate into enhanced reproductive performance following artificial insemination.