Efficacy of a stimbiotic and wheat bran as an additional fibre source on inflammatory cytokine gene expression and caecal microbiota composition in <i>Eimeria-challenged</i> broilers

1. Stimbiotic (STBX) supplementation may enhance nutrient utilisation by promoting non- starch polysaccharide fermentation. When combined with wheat bran (WB), it has been demonstrated to modulate the intestinal microbiota, enhance fibre degradation and improve gut health. The current study investigated the impact of STBX supplementation on immune responses and caecal microbiota composition of broilers fed diets with or without 50 g/kg wheat bran (WB) under an <i>Eimeria</i> challenge.2. A total of 1200 male 1 d old broiler chicks were randomly allocated to one of six treatments in a randomised complete block design: (1) 0% WB, no STBX, no challenge (NCH); (2) 0% WB, with STBX, no challenge (NCH-STBX); (3) 0% WB, no STBX, with challenge (CH); (4) 5% WB, no STBX, with challenge (CH-WB); (5) 0% WB, with STBX, with challenge (CH-STBX); and (6) 5% WB, with STBX, with challenge (CH-WB-STBX). On d 20, the spleen and on d 43, caecal contents were analysed for cytokine gene expression and microbiota composition, respectively.3. No significant effects of treatments on proinflammatory cytokines were observed. In contrast, there was only a tendency (<i>p</i> = 0.090) for changes in anti-inflammatory cytokine IL-10, where the expression was higher in NCH and NCH-STBX than in challenged treatment groups (<i>p</i> = 0.090). Treatments did not significantly influence microbial diversity. At the phylum level, relative abundance of <i>Firmicutes_A</i> (FDR - False Discovery Rate adjusted <i>p</i> = 0.003) and, at the family level, <i>Ruminococcaceae</i> was significantly higher (FDR adjusted <i>p</i> = 0.01) in NCH and NCH-STBX groups compared to CH-STBX, respectively. The relative abundance of <i>Lachnospiraceae</i> was significantly higher (FDR adjusted <i>p</i> = 0.010) in the NCH treatment group compared to the CH-STBX group. <i>Streptococcaceae</i> was significantly higher (FDR adjusted <i>p</i> = 0.013) in NCH and NCH-STBX groups than CH-WB-STBX.4. Supplementation with STBX had no significant effect on cytokine gene expression and microbial diversity, but specific microbes were affected by <i>Eimeria</i> infection. Under challenge, WB and STBX supported bacteria that ferment carbohydrates and increased predicted butyrate and fat metabolism, helping the gut microbiota adapt to stress.