| | The following article was presented during the Pre-Conference Nutrition Session before the 2016 Midwest Poultry Federation Convention in Saint-Paul on March15th. The information provided is helpful to an understanding of intestinal function and the benefits of supplementing with products that release butyric acid in the cecum and terminal ileum. | | |
Vanessa Iseri, PhD. Kemin Industries, Inc.
Introduction
Due to customer demands, producers have been asked to change the way they grow production animals, specifically through the removal of antibiotics. With this need comes necessary changes to animal production as a whole, starting with management, feed, and vaccination programs. To make those changes, an endless number of alternatives are being considered in order to meet the same feed efficiency, growth rate, and egg production standards that are accomplished with antibiotics. With that, comes a need to better understand how gut health is affected by these alternatives.
Factors that Contribute to Gut Health
Gut health in both human medicine and animal health has been defined in various ways. It was initially described that good gut health was the absence of illness. However, through our development of molecular tools and a better understanding of intestinal biology, it is clear that there are many factors that contribute to gut health. The intestinal barrier, microbiota and intestinal immunity can be considered the three main factors that attribute to gut health, but more importantly the interactions of these systems.
Soon after hatch, the chick’s gastrointestinal (GI) tract comes into contact with exogenous microorganisms and quickly develops into a complex microbial ecosystem. Each section along the intestinal tract contains distinct microbial communities, in which multiple species of Lactobacillus, Enterococcus and Clostridium mostly populate the ileum as opposed to species of Bacteroides, Bifidobacterium, and Clostridium in the cecum. The relationship between the host and microbiota can be described has a symbiotic one, in which both benefit. The host provides a protected, nutrient-rich environment which allows the microbiota to establish a diverse, yet remarkably resilient ecosystem. In return, the microbiota provides resistance to the colonization of pathogenic microbes, aid in the development and maintenance of intestinal and systemic immunity, support intestinal structure development, and produce nutritional factors.
Any dramatic shifts in the microbial population due to dietary changes, or pathogens can be detrimental to the host. The epithelial barrier has the large task of absorbing nutrients, yet at the same time protecting the host from invading pathogens, toxins, and antigens, as well as the abundant microbial populations in the intestine. Besides nutrient absorption and host protection, enterocytes are capable of acting as frontline sensors to microbial encounters in order to guide immune response. Specialized epithelial subsets enteroendocrine cells, goblet cells, Paneth cells, and M cells also contribute to maintaining a physical (i.e. mucus) and chemical barrier (i.e. β-defensins) between the outside environment and the host.
An important component to maintaining the intestinal barrier are tight junctions, which are made up of multifunctional protein complexes. Tight junctions seal the paracellular space between epithelial cells, thus preventing the translocation of microorganisms and other antigens across the epithelium. Tight junctions are highly dynamic structures, and their permeability is regulated by various factors such as diet, microbes, inflammation. With the continual exposure of microbiota and both dietary and environmental antigens, the intestinal immune system must balance between tolerance and responding to challenges. Thus, the intestinal immune system plays a huge role in overseeing the interactions between the host and the microbiota, through a network of immune cells, cytokines, chemokines and other immunological mediators.
Hooper and Macpherson describe the intestinal immune system as having three levels of protection each with distinct mechanisms. The first layer of protection is the secretion of chemical barriers, such as secretory IgA, that minimize the ability of bacteria to adhere to the epithelial lining. The second layer is the detection and elimination of bacteria that has translocated by phagocytic cells in addition to their role in intestinal wound healing. The third layer is the network of cells and immune proteins that allow the intestinal immune system to quickly respond to infection using minimal inflammation, and containing the infection at the intestinal level.
As mentioned above, the microbiota, epithelial barrier, and intestinal immune system are key factors that affect gut health, and the interactions of all three of these systems are necessary for both the development and maintenance of gut health. Key examples that illustrate this point are the development and maturation of the intestinal immune system through its interactions with the microbiota; epithelial homeostasis is based on its interactions with the microbiota; and the interactions of the intestinal immune system and epithelial barrier allow for the containment and stability of the microbial populations.