ISSUE FOCUS FEED & ADDITIVE MAGAZINE November 2022 37 MICROBIOME - IS IT THAT IMPORTANT? As it is common to think that probiotics, prebiotics, or synbiotics with one or a few strains are enough to maintain gut health, the concept of microbiota needs explanation. The intestinal microbiota can be defined as the collection of all microbes like bacteria, fungi, protozoa, and viruses that live in the gastrointestinal (GI) tract. Thanks to molecular tools, especially next-generation sequencing technologies, we can identify bacteria within the avian GI tract with greater precision that cannot be compared to bacterial culture limited by the commonly used laboratory media. It is estimated that less than 10% of intestinal bacteria can be cultured on routine media. A few well-known strains, like Salmonella and Campylobacter, are described as pathogens. What if they are not the most significant strains as we thought before? Mammalian microbiota can include more than 100 trillion bacterial cells. It means that the total sum of bacteria is approximately 10 times more than the number of host cells! The relationship between the microbiome and the host is very close. It forms a special kind of ecosystem that significantly impacts host health, including not only digestion but also the immune and nervous systems. Well-known processes of starch or pectin complex fibers fermentation into short-chain fatty acids (SCFA) performed by intestinal bacteria may serve as an energy source (propionate, acetate) for the intestinal epithelial cells of the host. SCFA maintain intestinal barrier function that minimizes bacterial translocation and activates minimizing bacterial translocation T cells in the GIT. Bacterial metabolites show plenty of properties that reach far beyond the gastrointestinal tract. Scientific research proved that there is a way of communication between the GIT and the brain. GUT-BRAIN AXIS Have you ever “gone with your gut” to make a decision? Perhaps you’ve felt “butterflies in your stomach” when nervous? What exactly was it? Your second brain, hidden in the walls of the digestive system, was the one that sent you signal. The “brain in your gut” concept explains the links between health, digestion, mood, and even the way you think or make decisions. The enteric nervous system (ENS) is formed by two thin layers of more than 100 million nerve cells in your gastrointestinal tract from its very beginning—the oesophagus—to its very end—the rectum. We think of ourselves as being in charge, but it’s not the whole truth. ENS controls the digestion, enzymes release, and breakdown of the feed as well as the blood flow necessary for the absorption of nutrients. But it does much more. As Jay Pasricha, M.D., director of the Johns Hopkins Center for Neurogastroenterology, explains, it can communicate back and forth with our big brain. The gut-brain axis is regulated by: cortisol, microbiota metabolites like SCFA, neurotransmitters like gamma-aminobutyric acid (GABA), acetylcholine or serotonin, and neuromodulators, for example, neuropeptide Y (NPY). Amongst other actions, NPY inhibits the activity of the hypothalamic paraventricular nucleus, thus contributing to increased feed intake. The communication is bidirectional. For example, neuroendocrine substances produced by the host during periods of stress may modulate the virulence of enteropathogens. What about animals?
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