Modulation of broiler gut microbiota and gene expression of Toll-like receptors and tight junction proteins by diet type and inclusion of phytogenics

This study evaluated the effect of reduced dietary energy (ME) and crude protein (CP) levels along with inclusion of a phytogenic feed additive (PFA) on gut microbiota composition and gene expression of Toll-like receptor(s) (TLR), tight junction proteins, and inflammatory cytokines expressed in secondary lymphoid organs. Depending on dietary ME and CP level down regulation and the inclusion or not of PFA at 125 mg/kg diet, 450 one-day-old male broilers were allocated in the following 6 treatments for 42 D according to a 3 x 2 factorial design: A: diet formulated optimally to meet broiler nutrient requirements; APh: A+PFA; B: suboptimal in ME and CP levels by 3%; BPh: B+PFA; C: suboptimal in ME and CP levels by 6%; CPh: C+PFA. Diet type and PFA supplementation were shown to affect mostly the mucosa-associated microbiota compared to the luminal ones. Ileal mucosa-associated total bacteria (P-D= 0.005), Lactobacillus spp. (P-D= 0.003), and Clostridium cluster XIVa (P-D= 0.009) were affected by diet type with broilers fed diet B having lower levels compared to broilers fed diets A or C. Moreover, diet type affected cecal mucosa-associated Lactobacillus spp. (P-D= 0.002) with broilers fed diet C having lower levels compared to broilers fed diets A or B. Supplementation with PFA resulted in higher levels of cecal mucosa-associated Bacteroides (P-P= 0.031), Clostridium cluster IV (P-P= 0.007), and Clostridium cluster XIVa (P-P= 0.039). Diet type affected TLR2 (P-D= 0.046) and claudin 5 (P-D= 0.027) in cecal epithelium. Lower TLR2 (P-P= 0.021) and higher zonula occludens 2 (P-P= 0.031) relative gene expressions were seen in ileal epithelium following PFA supplementation. Moreover, in cecal epithelium, PFA supplementation resulted in lower TLR2 (P-P < 0.001) and higher zonula occludens 2 (P-P= 0.009), claudin 5 (P-P= 0.005) and occludin (P-P= 0.039) relative gene expressions. There were no significant diet type and PFA effects on cytokines in secondary lymphoid organs, except for a dietary effect on transforming growth factor beta 4 (P-D= 0.023) in cecal tonsils. In conclusion, PFA inclusion beneficially modulated elements of gut microbiota, Toll-like signaling molecules and gut tight junction genes.