Significant differences (ANOVA, B–H FDR corrected p value: p < 0.05) in cumulative proportions of genus (a) Christensenellaceae_R-7_group, (b) Elsenbergiella, (c) Lachnoclostridium, and (d) Shuttleworthia in ceca microbiota of broiler chickens subjected to different treatments groups. Treatments include (A) negative control treatment—chicks fed a basal corn-soybean meal-wheat-based diet; (B) in-feed antibiotics—chicks fed NC + 0.05% bacitracin methylene disalicylate; (C) in-water essential oil—chicks supplied the essential oil via the water route at the recommended dosage of 250 mL/1000 L of drinking water; (D) in ovo saline treatment—eggs injected with 0.2 mL of physiological saline (0.9% NaCl); (E) in ovo essential oil treatment—eggs injected with 0.2 mL of a saline + essential oil blend mixture at a dilution ratio of 2:1; and (F) in ovo + in-water essential oil treatment—chicks offered the essential oil blend via the in ovo and in water route, successively.