Modified guchang decoction improves gut injury in Escherichia coli K88-challenged broilers by activating FXR and TGR5...

Gut injury imposes a heavy burden on the poultry industry. Modified guchang decoction (MGD), derived from classical guchang decoction for gut disease, has unclear gut effects and mechanisms in broilers. This study aimed to evaluate the impact of drinking water supplemented with MGD on growth performance, gut health, and Farnesoid X receptor (FXR) and Takeda G protein-coupled bile acid receptor 5 (TGR5) signalling pathways in broilers challenged with Escherichia coli K88 (E. coli K88). The experiment used 300 broilers, which were divided into five groups, including negative control (NC) group, E. coli-challenged (EC) group, antibiotic (AB, 1 g/L) group, MGD low-dose group (MGDL, 8 mL/L), and MGD high-dose group (MGDH, 16 mL/L). Each group included 6 replicates, each housing 10 broilers. From 11 to 13 d, broilers in the EC, AB, MGDL and MGDH groups were orally administered 1 mL of E. coli suspension (1 × 10⁹ CFU/mL) per broiler to establish the E. coli infection model. From 14 to 20 d, treatments were administered via drinking water. The experimental period lasted 28 days. Drinking water supplemented with MGD enhanced growth performance, immune organ indices, intestinal mucosal barrier, villus height and crypt depth in broilers. The MGDL group attenuated inflammatory responses, resulting in decreased concentrations of interleukin-8, interleukin-6, interleukin-1β, interferon-γ, tumour necrosis factor-α and lipopolysaccharides (P < 0.05) and increased concentrations of interleukin -10 (P < 0.05). In addition, drinking water supplemented with MGD decreased the expression of myeloid differentiation primary response 88, Toll-like receptor 4 and nuclear factor kappa B (P < 0.05), whereas it increased the expression of FXR and TGR5 (P < 0.05). Caecal microbiota sequencing showed that the MGDL group improved microbiota composition by downregulating harmful bacteria (g_Bacteroides and g_Enterococcus). Microbiota were associated with FXR and TGR5 signalling pathways, immune indicators and intestinal proteins (P < 0.05). Overall, drinking water supplemented with MGD mitigated gut damage in broilers challenged with E. coli K88 through the FXR and TGR5 signalling pathways.