Effects of Powder on the Growth Performance, Immune Organ Weights, Cecal Microbiology, Serum Immunoglobulins, and Tibia Minerals of Broiler Chickens.

A total of 640 one-day-old Cobb 500 MV × Cobb 500 FF mixed broilers were randomly assigned to one of four experimental treatments with four replicates per treatment and 40 birds per replicate for 32 days. The treatments consisted of a basal diet (control group), basal diet + 0.02% zinc bacitracin (AGP group), basal diet + 0.2% powder (GLP; 0.2% GLP group), and basal diet + 0.3% GLP (0.3% GLP group). The results showed that dietary 0.2% GLP supplementation increased body weight compared to the control and 0.3% GLP groups, and decreased feed conversion ratio (FCR) compared to the control group, during 19-32 days ( < 0.05). The feed intake was lower ( < 0.05) in both dietary GLP supplementation groups and the AGP group during 1-8 and 1-32 days compared to the control group. Additionally, the FCR was lower in the dietary GLP supplementation group (0.2%) and the AGP group ( < 0.05) compared to the control group. Moreover, the caeca of broiler chickens in the AGP and 0.2% GLP groups had a higher abundance of lactic acid bacteria (LAB). Supplementation of feed additives (AGP and GLP) increased the relative weight of the thymus, with no effect on the bursa of Fabricius and spleen. However, AGP supplementation decreased the serum IgM concentration, while supplementing a higher dose of GLP (0.3%) increased the ash content in the tibia. The findings indicate that 0.2% GLP is the recommended supplementation dose as a natural growth promoter to replace AGP in apparently normal chickens.