Developmental Regulation of chicken cathelicidins in the cecal tonsil. Cecal tonsils were harvested from broiler chickens of indicated age and subjected to RNA isolation and real-time PCR analysis of the expression of four cathelicidins. Fold differences in the cathelicidin expression level among different days after hatching were calculated relative to the expression level on day 7 using GAPDH as a reference gene. Each bar represents mean ± standard error of 3 to 5 chickens. The statistical significance was analyzed using one-way ANOVA followed by Tukey’s Test. *P < 0.05.