Tannic acid supplementation exerts biphasic effects on growth performance, immune function, and gut microbiota in Pekin duck

Tannins, which are polyphenols present in several plant species, have been shown to exert several beneficial effects in livestock at specific levels. However, the optimal dosage for growth promotion in waterfowl like Pekin ducks remains unclear. Therefore, this study aimed to investigate the effects of dietary tannic acid (TA) supplementation on the performance of Pekin ducks. A total of 420 male Pekin ducks were assigned to to five groups and fed a basal diet supplemented with 0, 0.1, 0.2, 0.35, or 0.5% TA (control, TAS0.1, TAS0.2, TAS0.35, and TAS0.5, respectively). Growth performance, serum biochemical, oxidative parameters, immune parameters, and cecal microbiota were analyzed. Low-to-moderate TA levels (0.1-0.35%) increased the pancreatic index (P < 0.05) and enhanced systemic antioxidant capacity, as evidenced by elevated activities of glutathione peroxidase, catalase, and total antioxidant capacity. Notably,0.1% TA supplementation increased serum immunoglobulin (IgA, IgG, IgM) and complement (C3, C4) levels compared to the control (P< 0.05). Conversely, dietary supplementation with 0.5% TA significantly compromised feed efficiency, increasing the feed conversion ratio by 14.6% during the initial 14-day period (P < 0.01). ​​​Importantly, TA intervention induced a dose-responsive restructuring of the cecal microbiota, characterized by a significant decrease in the relative abundance of Proteobacteria (P< 0.05), a marked reduction in the potentially pathogenic genus Desulfovibrio (from 6.24% to 0.17-2.14%, P< 0.01), and a selective enrichment of beneficial taxa, including Succinispira andRuminococcus. Functional predictions indicated enhanced xenobiotic metabolism in the low-dose groups but stress-related dysregulation in the TAS0.5 group. Collectively, these results demonstrate that TA exhibits dose-dependent biphasic effects. Optimal inclusion levels (0.1-0.35%) enhance antioxidant capacity, immune function, and gut microbial symbiosis, whereas excessive supplementation (0.5%) induces metabolic dysregulation and microbiota dysbiosis. Overall, this study established a theoretical framework for strategically optimizing TA supplementation in poultry production systems to reconcile productivity and health outcomes.