Effects of Tannic Acid on Immune Function and Gut Microbiota in Brandt’s Voles (Lasiopodomys brandtii)

The present study investigates the effects of tannic acid (TA) on body composition, immune function, and gut microbiota in Brandt's voles (<i>Lasiopodomys brandtii</i>); analyzes the gut microbiota-immune parameter associations during their response to plant secondary metabolites; and provides a theoretical basis for understanding their adaptive mechanisms. Thirty-three female Brandt's voles were randomly divided into four groups and intragastrically administered distilled water (control group) or TA at doses of 300, 600, and 1200 mg·kg^-1·d^-1 for 9 weeks. The results showed that TA had no significant effect on body mass, body composition (including subcutaneous, retroperitoneal, mesenteric, and perigonadal fat, as well as total fat mass), immune organ weights, or cellular immune responses in Brandt's voles. However, high-dose TA (1200 mg·kg^-1·d^-1) significantly reduced the serum anti-KLH IgG titers in a dose-dependent manner, indicating selective impairment of humoral immunity. High-dose TA (1200 mg·kg^-1·d^-1) also decreased the alpha diversity of the gut microbiota, with lower Chao1, Observed features, and Shannon indices compared to the control and low-dose (300 mg·kg^-1·d^-1) groups. Beta diversity analysis indicated that high-dose TA (1200 mg·kg^-1·d^-1) altered the overall gut microbiota structure, while taxonomic analyses revealed a decrease in Desulfobacterota and an increase in several gut-associated taxa, including Firmicutes, Clostridia, Lachnospirales, and Lachnospiraceae. In conclusion, high-dose TA (1200 mg·kg^-1·d^-1) induced significant changes in the gut microbiota and selectively suppressed humoral immunity. However, other immune parameters and growth-related measures remained unaffected. These findings suggest a potential role of gut microbial adjustments in modulating host responses to dietary TA and contribute to knowledge of the tolerance mechanisms in this species.