Postbiotics and Phytogenics as Functional Feed Additives: Impact on Gut Health and Growth Performance

Growing limitations on the use of in-feed antibiotics have accelerated the search for functional feed additives capable of supporting animal health and productivity under antibiotic-free production systems. Postbiotics, defined as non-viable microbial products or metabolic byproducts, and phytogenics, which are plant-derived bioactive compounds, have emerged as promising alternatives due to their stability and biological activity. Recent advances in the application of postbiotics and phytogenics in monogastric and ruminant nutrition are summarized, with emphasis on their mechanisms of action, synergistic effects, and impacts on gut health, immune function, and growth performance. Postbiotics modulate the gut microbiota, enhance epithelial barrier integrity, and regulate immune signaling, whereas phytogenic compounds provide antimicrobial, antioxidant, and digestive-stimulant effects. Available evidence suggests that combined strategies can enhance efficacy, particularly under production-related stress. Key challenges related to formulation, dose–response relationships, stability, and regulatory classification are discussed together with emerging omics-based approaches that support precision formulation. Overall, integration of multi-omics evidence with formulation and regulatory considerations supports the practical use of postbiotics and phytogenics in commercial livestock systems.