Carbohydrate-degrading multi-enzyme preparations (MEP) are used to improve broiler performances. Their mode of action is complex and not fully understood. In this study, we compared the effect of water-soluble fractions isolated at the pilot scale from wheat grain incubated with (WE) and without (WC) MEP. The fractions were incorporated in a wheat-based diet (0.1% w/w) to feed Ross PM3 broilers and compared with a non-supplemented control group (NC). The body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR) until d 14 were determined. At d 14, ileal and cecal contents and tissue samples were collected from euthanized animals. The intestinal contents were used to measure the short-chain fatty acids (SCFA) concentration using gas chromatography and to determine the abundance and composition of microbiota using 16S sequencing. Villi length of ileal samples was measured, while L-cell and T-cell densities were determined using immuno-histochemistry. The MEP treatment increased the amount of water-soluble arabinoxylans (AX) and reduced their molecular weight while retaining their polymer behavior. The WE fraction significantly (P < 0.05) increased FI by 13.8% and BWG by 14.7% during the first wk post hatch when compared to NC. No significant effect on FCR was recorded during the trial. The WE increased the abundance of Enterococcus durans and Candidatus arthromitus in the ileum and of bacteria within the Lachnospiraceae and Ruminococcaceae families, containing abundant butyrate-producing bacteria, in the ceca. It also increased the concentration of SCFA in the ceca, decreased the T-lymphocyte infiltration in the intestinal mucosa, and increased the glucagon-like-peptide-2 (GLP-2)-producing L-cell density in the ileal epithelium compared with WC and NC. No significant effects were observed on villi length. These results showed that AX present in the WE fraction altered the microbiota composition towards butyrate producers in the ceca. Butyrate may be responsible for the reduction of inflammation, as suggested by the decrease in T-lymphocyte infiltration, which may explain the higher feed intake leading to improved animal growth.