Antibiotic growth promoters (AGPs) have traditionally been incorporated into livestock diets to improve growth and feed utilization, through their effects on the microbial population of the gastrointestinal tract. However, their prolonged and routine use has contributed to the emergence and spread of antimicrobial resistance. Consequently, current efforts are focused not only towards finding suitable substitutes for AGPs but also towards minimizing the dependence on antibiotics in animal production. Plant-based products have received considerable attention as potential alternatives. Phytogenic feed additives (PFAs) include herbs, spices, essential oils and various plant extracts containing biologically active compounds. Research conducted in different animal species indicates that these substances may exhibit antimicrobial, antiviral, antioxidant and anti-inflammatory properties and may also influence feed palatability, intestinal health and gut development. But the precise biological mechanisms responsible for many of these effects are not yet completely understood.