Recent trends in the use of Bacillus species as probiotics in animal production: an overview

The increasing prevalence of antimicrobial resistance (AMR), growing concerns regarding antimicrobial residues, and restrictions on the use of antibiotic growth promoters have intensified the search for safe and sustainable alternatives in animal production. Among the diverse probiotic microorganisms investigated for this purpose, Bacillus species have attracted particular attention because of their endospore-forming capacity, resistance to processing and gastrointestinal stresses, and broad range of functional activities. This review summarizes recent trends in the application of Bacillus-based probiotics across animal production systems, with emphasis on their mechanisms of action, functional benefits, technological advances, challenges, and future prospects. Species including Bacillus subtilis, B. licheniformis, B. amyloliquefaciens, B. coagulans, and B. clausii have been investigated in poultry, swine, ruminants, aquaculture, insects, and companion animals, with reported effects on intestinal microbial homeostasis, nutrient digestion and utilization, immune modulation, pathogen suppression, intestinal barrier integrity, and production performance. Recent advances in genomics, metagenomics, microbiome research, synbiotic formulations, encapsulation technologies, and precision livestock farming are expanding opportunities for strain-specific selection and targeted probiotic application. Evidence from experimental and production studies indicates that appropriately selected Bacillus strains can improve growth performance, feed efficiency, nutrient utilization, disease resistance, and selected environmental outcomes while potentially reducing dependence on conventional antimicrobial interventions. Nevertheless, substantial challenges remain, particularly regarding strain-specific efficacy, safety and genomic characterization, consistency under commercial conditions, formulation, dose optimization, and regulatory harmonization. Overall, Bacillus-based probiotics represent a promising multifunctional approach for supporting animal health and productivity and contributing to more sustainable and antimicrobial-responsible animal production systems.