Abstract
BACKGROUND AND AIM: Antimicrobial resistance in poultry farms is a significant global public health concern that has led farmers to explore alternative antibiotics, such as prebiotics in poultry production. This study aimed to examine the antimicrobial activity of ethanolic shallot extract (ESE) and the effects of adding shallot powder (SP) to broiler feed on broiler growth, immune response to Newcastle disease virus (NDV) vaccination, and gastrointestinal tract bacteria. MATERIALS AND METHODS: We determined the antimicrobial effects of ESE against Escherichia coli O157:H7 (EOH) and Lactobacillus acidophilus TISTR 2365 (L2365) using the agar well diffusion method. We used a complete randomized design to assign 120 1-day-old Arbor Acre chicks to six groups with four replicates of five broiler chickens over 42 days. The treatment groups were as follows: T1-basal diet (B) + NDV vaccination (positive control), T2-B (negative control), T3-B + 2 g SP per kg of feed, T4-B + 2 g SP per kg of feed + NDV, T5-B + 4 g SP per kg of feed, and T6-B + 4 g SP per kg of feed + NDV. RESULTS: The minimum inhibitory concentrations of ESE on EOH and L2365 were 62.50 and 125.00 mg/mL, respectively. The body weight gain, average daily gain, and feed conversion ratio in the 4 g SP of T5 and T6 groups were significantly improved compared with the other groups (p < 0.05). The immune organ (IO) and thymus gland weights in the T4 group were significantly greater than those observed in the positive and negative control groups (p < 0.05). The IO weights of the bursae of Fabricius and spleen tended to be greater in the T4 group than in the other groups. T5 group broilers had the highest ratio of villus height to crypt depth. The humoral immunity titers against NDV vaccination were improved in the SP-supplemented groups compared with the non-supplemented groups (p > 0.05). SP supplementation reduced the levels of coliform (p < 0.05) and E. coli in the broiler intestine by adding 4 g of SP per kg of feed. However, L2365 was more tolerant to ESE in vitro and tended to increase in line with increased SP levels. CONCLUSION: ESE showed strong antimicrobial activity to reduce harmful bacteria, and SP supplementation may exhibit prebiotic effects to increase broiler chicken growth, immunity, and microbial balance.