Xylanase and Bacillus subtilis PB6 modulate microbiota and short-chain fatty acid profiles in broilers under necrotic...

Necrotic enteritis (NE) is a major poultry disease affecting profitability. Managing NE has become harder due to restrictions on in-feed antibiotics, which traditionally support gut health and production in broilers. To address this, a study was conducted to evaluate the effect of xylanase (Xy) and Bacillus subtilis (Pb) supplementation in a corn-soybean-based diet on the intestinal health of broiler chickens under NE challenge. A total of 630-d-old mixed-sex Cobb 500 broiler chicks were assigned to a 2 × 2 + 1 factorial design, giving five treatments: NE challenge without additives (CC); NE challenge with Xy (0.03%) (Xy); NE challenge with Pb (0.05%) (Pb); NE challenge with Xy (0.03%) and Pb (0.05%) (Xy+Pb); and non-challenge birds without additives (NC). NE challenge significantly increased serum fluorescein isothiocyanate dextran (FITC-d; P < 0.05), as well as ileal lactate, succinate, and total short-chain fatty acids (SCFA) concentrations (P < 0.05), while downregulating immunoglobulin A (IgA) and mucin 2 (MUC2) (P < 0.05). Pairwise permutational multivariate analysis of variance (PERMANOVA) showed distinct microbial profiles between the NC and CC groups (P < 0.05; unweighted and weighted UniFrac). Supplementation of Pb altered beta diversity compared with the CC, showing greater distances (weighted UniFrac; P < 0.05). It also shifted the relative abundances of Ruminococcaceae and Faecalibacterium towards NC levels, with no significant differences from either CC or NC groups (P > 0.05). Dietary Pb increased (P < 0.05) ileal lactate and total SCFA concentrations, irrespective of NE challenge. Dietary Xy significantly reduced Lachnospiraceae UCG 010 relative to CC birds (P < 0.05). It also showed tendencies towards lowering caecal propionate, iso-butyrate, and iso-valeric concentrations, and decreasing interferon gamma (IFN-γ) gene expression (P < 0.1). Overall, these results indicate that both Xy and Pb may help mitigate the adverse effects of NE by modulating gut microbiota and, thus, gut health. However, Pb showed greater and more consistent effects on SCFA production, microbiota diversity, and beneficial bacteria populations, highlighting its greater efficacy under NE challenge.