The relative abundance of microbiota at phylum level in the ileal chymus (IC), ileal mucosa (IM), and caecal chymus (CC) as affected by the age of chickens and dietary treatments (C—Control, Br—Broilact®, Sy—Synbiotic feed additive). Microbial composition at different taxonomical levels and in different intestinal samples (IC, IM and CC) were compared using two-way ANOVA test with Tukey’s HSD multiple group comparison’s post hoc test, using the dietary treatments (C, Br and Sy) and the age of birds (7, 14, 21, and 40 day) as main factors. The differences were considered significant at a level of p ≤ 0.05.