摘要Three hundred thirty-six Ross 308 male broiler chicks were used in a 21-d study to explore performance and gut function when treated with a proton pump inhibitor(PPI;0 or 89 mg/kg)in a 2×2 factorial arrangement with a xylanase(Xyl;0 or 0.1 g/kg)to determine if the beneficial activity of arabinoxylan(AX)depolymerisation,through arabinoxylo-oligosaccharides(AXOS)production,starts in the upper gastrointestinal tract.Treatment with the PPI started from d 14,and by d 21 animal performance had deteriorated(P＜0.001).An interaction was observed between PPI and Xyl for feed conversion ratio(FCR)(P＜0.05),whereby the combination reduced the negative effect of PPI on FCR.Application of PPI raised digesta pH in the gizzard and caecum(P＜0.05),increased protein concentrations in the lower gut(P＜0.05)and reduced intake of digestible nutrients(P＜0.05).Caecal concentrations of indole,p-cresol,ammonia and the ratio of total volatile fatty acid(VFA)to butyric acid were increased with PPI(P＜0.05),indicating enhanced protein fermentation.Xylanase activity in the digesta were greatest in the caeca,especially when Xyl was supplemented(P＜0.001).The concentration of total soluble AX was greater in the gizzard and ileal digesta with Xyl supplementation(P＜0.05),supporting the depolymerisation action of xylanase even under acidic conditions.These data suggest xylanase may function in the gizzard even though pH is not optimal for activity and emphasises the importance of chlorohydric acid secretions in ensuring overall optimum gut function.AX depolymerisation benefits animal performance although it is still unknown how the AXOS produced with xylanase supplementation in the upper gastrointestinal tract influence the microbial populations and overall gut functionality.