ABSTRACT

Background and Aim: The widespread restriction of antibiotic growth promoters (AGPs) in poultry production has accelerated the search for sustainable nutritional strategies that enhance bird health while maintaining productivity. Among these alternatives, probiotics have emerged as promising functional feed additives because of their ability to modulate the gut–immune axis, improve intestinal homeostasis, and strengthen host defense mechanisms. This review provides a comprehensive synthesis of current evidence regarding the immunomodulatory mechanisms of probiotics and their potential as sustainable alternatives to AGPs in poultry production. Relevant peer-reviewed studies published between 2000 and 2025 were critically evaluated to summarize the effects of probiotic supplementation on gut microbiota composition, intestinal barrier integrity, innate and adaptive immune responses, disease resistance, and production performance. The review highlights the strain-specific actions of commonly used probiotic genera, including Lactobacillus, Bacillus, Bifidobacterium, Enterococcus, and Saccharomyces, emphasizing their roles in competitive exclusion of pathogens, production of antimicrobial metabolites, regulation of cytokine expression, enhancement of mucosal and systemic antibody responses, and maintenance of immune homeostasis. Emerging evidence on postbiotics, paraprobiotics, synbiotics, and precision nutritional approaches is also discussed as part of next-generation strategies for improving poultry health. Although numerous studies demonstrate beneficial effects of probiotics on intestinal morphology, immune function, vaccine responsiveness, oxidative stress, and resistance to enteric pathogens, considerable variability remains due to differences in probiotic strains, dosage, supplementation period, bird genotype, management practices, and experimental conditions. These inconsistencies highlight the need for standardized strain characterization, optimized administration protocols, and long-term commercial validation to improve reproducibility and field application. Overall, probiotics represent an effective and environmentally sustainable approach for supporting poultry health while reducing dependence on antibiotics. Continued advances in molecular biology, microbiome research, precision livestock farming, and artificial intelligence are expected to facilitate the development of targeted probiotic interventions that enhance disease resistance, improve production efficiency, promote animal welfare, and contribute to sustainable poultry production systems. 

Keywords: antibiotic alternatives, disease resistance, gut health, immune modulation, microbiota, poultry, probiotics, sustainable production.