ISSUE FOCUS FEED & ADDITIVE MAGAZINE February 2023 39 in the absence of any overt disease in the gastrointestinal tract. WHY DOES GUT HEALTH MATTER SO MUCH? Gut health is extremely important because the gastrointestinal tract is the organ that has the largest contact surface with the environment, providing an effective barrier function that reduces exposure to harmful environmental elements and potential pathogenic agents, while allowing the absorption of nutrients and the excretion of waste substances. In other words, the correct functioning of the gut is the basis for appropriate nutrition and, consequently, a proper metabolism of the animal organism, as well as an extremely important defense barrier for that same organism. Both main gastrointestinal functions (feeding and defending) are two fundamental pillars for the growth and development of animals. IMPACT OF GUT HEALTH ON THE OVERALL HEALTH OF ANIMALS More than 2,000 years ago, Hippocrates — the father of modern medicine — suggested that all disease begins in the gut. Perhaps the famous Greek physician exaggerated a little bit, although evidence does show that many systemic and metabolic diseases begin in the gut. If the gastrointestinal tract does not function properly, the general health of the animal organism will be harmed in one way or another. But how does that happen? The gastrointestinal tract is not a compartment isolated from the rest of the animal organism, but there are numerous links between the key components of the gut and the rest of the body. In this sense, the gut environment provides a platform for the growth of a diverse microbiota that is not only a barrier against colonization by pathogens, but also supplies relevant metabolites (including neurotransmitters) and nutrients (e.g., short chain fatty acids, vitamins) for the host animal. In addition, the gut microbiota regulates the immune response locally through its direct interaction with the mucosal immune system and GALT components, as well as systemically. There are direct and indirect mechanisms by which the intestinal microbiota contributes to immune responses systemically, at distant
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