| Summary: | Two 21-day experiments were conducted to investigate the effects of exogenous enzymes on growth performance, tight junctions, and nutrient transporters, jejunal oligosaccharides and cecal short-chain fatty acids (SCFA) of broiler chickens challenged with mixed <i>Eimeria</i>. Two different basal diets: high fiber-adequate protein (HFAP; Expt. 1) or low fiber-low protein (LFLP; Expt. 2) were used in the two experiments. In each experiment, birds were allocated to four treatments in a 2 × 2 factorial arrangement (with or without protease and xylanase combination; with or without <i>Eimeria</i> challenge). In Expt. 1, with HFAP diets, <i>Eimeria</i> upregulated (<i>p</i> < 0.05) the expression of claudin-1, but downregulated (<i>p</i> < 0.05) glucose transporters GLUT2/GLUT5. On the contrary, enzymes downregulated (<i>p</i> < 0.05) claudin-1 and alleviated the <i>Eimeria</i>-depressed GLUT2/GLUT5 expression. In both experiments, <i>Eimeria</i> decreased (<i>p</i> < 0.05) cecal saccharolytic SCFA and increased (<i>p</i> < 0.05) cecal branched-chain fatty acids. The challenge × enzyme interaction (<i>p</i> < 0.05) showed that enzymes reversed the <i>Eimeria</i> effects on fermentation pattern shift. In conclusion, <i>Eimeria</i> altered tight junctions and nutrient transporters expression promoted cecal proteolytic fermentation and inhibited saccharolytic fermentation. Exogenous enzymes showed the potential of alleviating the <i>Eimeria</i>-induced intestinal gene expression changes and reversing the unfavorable cecal fermentation pattern.
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