Effect of dietary propolis (PR) supplementation on (a) total white blood cells (TWBC) count, (b) heterophil to lymphocyte (H/L) ratio, and (c) leukocyte cell viability (LCV) of broiler chickens challenged with Escherichia coli (EC) infection. Bars express the mean (n = 20) with standard error (SE). Means with dissimilar letters significantly differ at p < 0.05. Treatment groups: C, control group without PR supplementation or EC challenge; EC, group without PR supplementation but challenged with EC; PR, group supplemented with PR but not challenged with EC; PR+EC, group supplemented with PR and challenged with EC.