GCG and infection: Based on the main-effect NE challenge, NE infection notably downregulated occludin, zonula occludens-1 (ZO-1), epithelial cell growth factor receptor (EGFR) and mucin-2 mRNA levels and remarkably upregulated GLP-2 and IGF-2 mRNA levels in the jejunum (P < 0.05) compared with those in the unchallenged groups (P < 0.05).