Multifaceted Applications of Lactobacillus acidophilus in the Global Livestock Industry: Mechanisms, Species-Specific Effects, and Sustainable Production

The global restriction or elimination of antibiotic growth promoters (AGPs) has intensified the search for effective and sustainable alternatives in livestock production. Among the proposed strategies, probiotic supplementation has received increasing attention due to its potential to enhance animal health and productivity while reducing reliance on antibiotics. Lactobacillus acidophilus (L. acidophilus), a well-characterized lactic acid bacterium commonly found in the gastrointestinal tract of animals, has been widely investigated as a probiotic candidate in livestock systems. This review summarizes current knowledge regarding the biological characteristics and mechanisms of action of L. acidophilus, including pathogen inhibition, modulation of intestinal barrier function, and regulation of host immune responses. Practical considerations, including the effects of feed processing on bacterial viability, strain stabilization technologies, and dose–response relationships, are also discussed. Reported supplementation doses in livestock trials typically range from 106 to 109 CFU/kg feed or per animal per day, although dose–response relationships remain poorly defined. Furthermore, recent advances in the application of L. acidophilus in major livestock species—including swine, poultry, and ruminants—are critically evaluated, with emphasis on growth performance, gut microbiota modulation, and disease resistance. Emerging approaches such as postbiotic utilization and probiotic-based vaccine adjuvants are also discussed. In addition, the potential contribution of L. acidophilus to environmental sustainability and mitigation of antimicrobial resistance dissemination in livestock systems is examined. Overall, L. acidophilus represents a promising component of integrated strategies aimed at improving animal health and promoting sustainable livestock production, although further research is required to clarify strain-specific effects and optimize practical applications.