Dietary gallnut tannic acid supplementation improves boar semen quality by regulating antioxidant status, hormone secretion, and seminal plasma metabolome.

Boar spermatozoa are highly susceptible to oxidative damage, which compromises semen quality. Gallnut tannic acid (GTA) possesses potent antioxidant and antimicrobial activities. This study aimed to comprehensively investigate the effects of dietary GTA supplementation on boar semen quality, antioxidant status, hormone secretion, and seminal plasma metabolome. Twenty-eight boars were divided equally into four groups fed a basal diet with 0 (CON), 0.05% (G1), 0.1% (G2), or 0.2% GTA (G3) for 12 weeks. Dietary GTA supplementation significantly enhanced semen quality. At week 12, sperm motility, sperm concentration, total sperm count and effective sperm count were all significantly higher, while the percentage of non-progressive sperm motility was significantly lower, in all GTA-treated groups relative to the CON group (P < 0.05). For ambient-temperature semen preservation at 17 °C, the G2 and G3 groups showed a markedly lower proportion of slowly motile sperm after 24 h of storage, and all GTA groups maintained reduced slow motility after 72 h of storage (P < 0.05), with the 0.2% GTA treatment delivering the strongest protective effect during storage. By week 12, GTA dramatically decreased malondialdehyde (MDA) content and enhanced glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities in both serum and seminal plasma (P < 0.05), alongside significantly elevated serum testosterone levels in all GTA groups (P < 0.05). Metabolomic analysis revealed that GTA supplementation mainly influenced pathways related to energy metabolism and amino acid metabolism. In conclusion, dietary GTA supplementation effectively improves boar semen quality and extends the shelf-life of preserved semen by strengthening redox status, boosting testosterone levels, and optimizing seminal plasma metabolic homeostasis. A supplemental dose of 0.2% GTA is recommended as the optimal regimen for boar diets. These findings support GTA as a promising natural nutritional strategy to improve boar fertility in commercial swine production. Further studies are warranted to elucidate the detailed regulatory mechanisms by which GTA modulates the hypothalamic-pituitary-gonadal axis and the gut-reproductive axis.