Synergistic Effects of Garlic Extract and Mannan‐Oligosaccharide Prebiotic Supplementation on Growth Performance, Carcass Quality, Immunity, Gut Morphology and Microbiome in Broiler Chickens

This study evaluated the effects of dietary supplementation with garlic extract, mannan oligosaccharide (MOS) and their combinations on growth performance, immunity, gut morphology and microbiota in broilers. A total of 250 Hubbard chicks were allocated into five groups: control (basal diet), garlic extract, MOS, Combo-I (half doses of both) and Combo-II (full doses of both). The trial lasted 42 days under standard management conditions. Results demonstrated that Combo-I consistently improved body weight gain and feed conversion ratio (FCR) during the starter, grower and finisher phases (p < 0.05), highlighting a synergistic effect of the combined supplements. Carcass weight was significantly enhanced in Combo-II (p = 0.03), although dressing percentage and organ weights were not affected (p > 0.05). Immunological parameters were strongly influenced by supplementation. Combo-I induced the highest antibody titres against Newcastle disease and infectious bursal disease (p < 0.05), with Combo-II ranking second, whereas single additives showed moderate improvements compared to the control. Similarly, serum immunoglobulin concentrations (IgM, IgA and IgG) were greatest in Combo-I, confirming enhanced humoral immunity. Gut morphology was significantly improved in the combination groups, particularly Combo-I, which showed increased villus height, wider villi, reduced crypt depth, and the highest villus:crypt ratio (p < 0.05), reflecting superior absorptive potential. Although differences in ileal microbiota were not statistically significant, both combination treatments reduced Escherichia coli and Salmonella counts while promoting Lactobacillus spp. populations. In conclusion, the combined use of garlic extract and MOS, especially at half doses (Combo-I), optimally improved growth, immune response, gut architecture and microbial balance, offering a synergistic strategy for enhancing broiler performance.