It is important that alternatives to antimicrobials for animal growth promotion are found, raising the need for a deeper understanding of the microflora physiology and interaction with the host. In this perspective, non-conventional feed additives do not have to dramatically alter the activity of the intestinal microflora, but rather have to modulate the ecosystem in which potentially toxic compounds are produced, and improve the balance of beneficial bacteria showing interesting and welldefined phenotypes. Dietary characteristics, environmental hygiene, and the risk of inducing a resistant response should all be carefully considered when designing a long-term strategy. The roles of organic acids, non-digestible oligosaccharides and natural antimicrobials are discussed.