Probiotics as sustainable alternatives to antibiotic growth promoters: Mechanisms, applications, and future perspectives in livestock production

This narrative review systematically summarizes the current knowledge about probiotics as scientifically defined alternatives to conventional antibiotic growth promoters (AGPs) in modern livestock farming. Globally, there is an increase in demand for AGP-free livestock due to growing threat of antimicrobial resistance. Although ample literature is available on efficacy of probiotics as AGP alternatives, there is a paucity of comprehensive data on strain-specific modes of action, effective dose regimens, and standardized application protocols across wide variety of livestock species. Probiotics exert complex antimicrobial mechanisms, including direct pathogen antagonism, gut microbiome modulation, intestinal barrier enhancement, immune system stimulation, and metabolic optimisation. In ruminants, poultry, pig, and rabbits, the application of probiotics has repeatedly shown improved growth performance, increased resistance to disease, better breeding performance and so on. Most of the literature available shows positive results on rumen fermentation, caecal microbiota composition, nutrient digestibility, and immunological responses. Nonetheless, knowledge gaps remain in the areas of interaction with the environment, production standardisation, and long-term effects of sustainability. Sustainability elements include less development of antimicrobial resistance, reduced environmental impact due to more efficient resource use, and improved economic viability. However, variations in strain-specific probiotic efficacy, environment-dependent outcomes of probiotic applications, and lack of production standardisation remain the challenges. Emerging innovations, such as postbiotics, precision livestock farming integration using AI, Internet of Things, and multi-strain synbiotic formulations offer promising solutions. This review summarises opportunities and challenges associated with probiotic use in livestock production systems and underscores their potential to revolutionise sustainable animal agriculture, as well as deal with serious public health concern of antimicrobial resistance.