Abstract
Background:
The global poultry industry is under pressure to reduce its reliance on antibiotics, necessitating the search for effective alternatives. Pathogenic Escherichia coli infections remain a major challenge, leading to significant economic losses due to impaired growth performance and increased mortality.

Aim:
This study aimed to evaluate the efficacy of shallot extract (Allium cepa L.) fermented by Lactiplantibacillus plantarum 1582 (FS) as a potential antibiotic alternative in experimentally challenged E. coli broiler chickens.

Methods:
A total of 300 1-day-old J-Dabaco broilers were randomized to six treatments (n = 50; five replicates of 10): nonchallenged control (NC), challenged control (PC), antibiotic control (AB), and three challenged groups receiving FS at 1%, 2%, or 3% (FS1 - FS3). Challenged birds were orally inoculated with E. coli ExPEC_A338 (3 × 108 CFU/mL) on days 7 and 8. Outcomes included growth performance, cecal microbiota, jejunal histomorphology, immune-organ indices, serum IgM, IgA, and IgG levels, and mRNA expression of tight-junction proteins (ZO-1, occludin, and claudin-2) and cytokines (IL-4, IL-1β, TNF-α, IFN-γ).

Results:
Supplementation with FS, especially the 3% dose (FS3), significantly improved BWG by 9.4% and restored survival to 100%, matching the NC and AB groups. FS3 enhanced gut health by reducing the densities of pathogenic E. coli and Salmonella spp. while simultaneously increasing the densities of beneficial Lactobacillus spp. (P < 0.05). Morphological analysis showed that the FS3 group had the highest villus height (1049.86 µm) and VH/Crypt Depth (CD) ratio (13.05) (P < 0.05). Although immune-organ indices remained unchanged, dietary FS at 2 - 3% significantly upregulated ZO-1, while IFN-γ increased at 1% FS (FS1) but remained comparable to the challenged control at 2 – 3% (P<0.05). Serum IgM increased at 1%–2% and serum IgA decreased at 3% (P < 0.05).

Conclusion:
Collectively, these findings demonstrate that L. plantarum-fermented shallot extract, particularly at a 3% inclusion level, represents a promising non-antibiotic strategy for broilers challenged with E. coli, primarily through enhanced growth performance intestinal integrity and a favorable gut microbial balance.

Key words: Antibiotic alternative; Broiler; Escherichia coli; Fermentation; Lactiplantibacillus plantarum.