CASP3 and infection: Compared with the CON group, chick infection with E. coli increased the expression of Bax (P < 0.05) in the spleen and ileum, caspase 3 (P < 0.05) in the liver and jejunum, and caspase 8 (P < 0.05) in the liver, spleen, and ileum; decreased the expression of Bcl2 (P < 0.05) in the liver, spleen, jejunum, and ileum; and decreased the ratio of Bcl2/Bax (P < 0.05) in the spleen, jejunum, and ileum.