Tannic acid-mediated gut microbes for enhanced intestinal immunity in Escherichia coli-challenged weaned piglets

Tannic acid (TA) has astringent functions and prevents diarrhea in piglets. This study investigated the mechanism of different TA levels (0, 0.01%, 0.05%, 0.25%) in low-protein diets on growth performance and intestinal barrier function by regulating gut microbiota in weaned piglets challenged with Escherichia coli (E. coli). We found that low-protein dietary supplemented with different levels of TA enhanced the growth performance of weaned piglets to some degree (P < 0.10) and significantly reduced the incidence of diarrhea under both normal and E. coli-challenged conditions (P < 0.05), but its effects on nutrient digestibility in piglets were not significant (P > 0.05). The addition of 0.05% TA effectively preserved intestinal morphological integrity and decreased serum LPS, IL-1β, and TNF-α levels, as well as increasing serum IgM and IgA concentrations in E. coli K88-challenged piglets (P < 0.05). Moreover, TA supplementation increased gene expression related to tight junctions and water channels in the ileum or colon, as well as inhibiting the TLR4/MyD88/NF-κB inflammatory pathway in the ileum (P < 0.05). Additionally, dietary TA supplementation altered the diversity and structural composition of microbes in the colonic chyme of E. coli K88-induced piglets. At the genus level, TA treatment increased the abundance of Ruminococcaceae_UCG_005, Ruminococcaceae_UCG_002, and Ruminococcaceae_NK4A214_group, while E. coli challenge decreased Lachnospiraceae_XPB1014_group and Prevotellaceae_NK3B31_group abundance, and the abundance of these differentially microorganisms was significantly correlated with immune parameters (P < 0.05). These results indicated that adding 0.05% TA to low-protein diets without antibiotics could alleviate E. coli infection and improve immunity in piglets by regulating gut microbiota and the TLR4/MyD88/NF-κB pathway. This study provides a novel nutritional strategy utilizing TA as a promising antibiotic alternative in low-protein diets to combat post-weaning diarrhea and promote intestinal health in piglets.