All animals face constant changes and challenges to their health. The maintenance of a healthy homeostatic state within the gut is important, not only to the gastrointestinal (GI) tract, but it also can affect such diverse systems such as the respiratory and reproductive system. We also know that it can affect the brain and the skin health as well. The GI tract and remote organs in the body share bidirectional communication via immune, neural, endocrine or metabolic links called the “gut-organ axis.”

The GI tract faces more potential challenges than do other systems due to its interactions with many more and more diverse species of microorganisms than faced by other systems. Seventy percent of the immune system is found in the digestive tract. Within the GI tract, threats can be found: Pathogenic bacteria that can both damage the digestive tract directly or if absorbed, because of poor gut integrity, can cause disease and defective actions by other organs. For example, the absorption of Fusobacterium necrophorum, a gram-negative, obligate anaerobic bacterium, can cause liver abscesses and reduce liver efficiency. We also know that Clostridium perfringens is an opportunistic bacterium that can produce exotoxins that can damage the cell walls of the digestive tract. To help keep these pathogenic bacteria “in check,” the body not only relies on its’ own immune system but also relies on a healthy biome, a mixture of beneficial and benign bacteria. There is a homeostatic state that allows proper absorption of nutrients and general operation of the GI tract. Unfortunately, when there is a challenge to the GI tract, the activities the GI tract uses to protect itself can take nutrients and activated cells that may leave other systems at greater risk. Additionally, the production of cytokines and interleukins send signals, causing reaction in other tissues.

Gut health is known to affect the nervous system via the “gut-brain axis.” Inflammation originating in gut can result in inflammation of nervous tissue including the brain itself. In humans, it has been linked to multiple sclerosis, Alzheimer’s and Parkinson’s diseases, as well as anxiety and depressive-like disorders. Messages also travel from the brain back to the GI tract via the vagus nerve, which can affect gut motility. Although correlation is not necessarily causation, it is interesting that there is a link between the human microbiota in the gut and mental health. In patients suffering from depressive disorder, levels of Enterobacteriaceae and Alistipes ("bad" bacteria) were enhanced, while the level of Faecalibacterium ("good" bacteria) was reduced. The researchers also found that there was less diversity in gut bacteria in patients with mental disorders, as well as a decrease in bacteria producing short chain fatty acids.1 A 2017 study2 found a link between gut microbiome composition and cognition in older adults. Individuals with lower proportions of Bacteroidetes and Proteobacteria and higher proportions of Firmicutes and Verrucomicrobia performed significantly better on tests associated with attention, learning and memory.

There is also a gut-lung axis. Both the respiratory system and the gut system have a microbiome that they are associated with, albeit the lung biome has less numbers and diversity than the gut biome.3 Both microbiomes can result in anti-inflammatory actions and both can result in inflammatory actions, such as those induced by lipopolysaccharides (LSP) otherwise known as endotoxins. Cytokines released because of the local situation can also affect the other tissue and biome. A study in dairy calves demonstrated that compounds designed to reduce gut inflammation resulted in a significant decrease in respiratory disease.4

A gut-reproduction axis also exists. A nationwide study of American women revealed that dysbiotic conditions in the vagina were significantly associated with periodontitis indicating a link between these two tissues.5 The production of short-chain fatty acids (SCFA) are generally a positive thing in the gut, both inhibiting pathogenic bacteria and enhancing absorption of nutrients. However, SCFA have a negative effect on vaginal biome, and transfer from the gut to vagina can have negative effects. Infection of G. vaginalis in murine vaginas increased the concentration of TNF-α and myeloperoxidase activity and decreased the concentration of IL-10 in colon tissue. “The microbiota plays a major role in the reproductive endocrine system throughout a woman’s lifetime by interacting with estrogen, androgens, insulin and other hormones. Imbalance of the gut microbiota composition can lead to several diseases and conditions, such as pregnancy complications, adverse pregnancy outcomes, polycystic ovary syndrome (PCOS), endometriosis and cancer; however, research on the mechanisms is limited.” 6


The mechanisms by which intestinal microbiota exert their influence on skin homeostasis appear to be related to the modulatory effect of gut commensals on systemic immunity. In cases of disturbed intestinal barriers, intestinal bacteria as well as intestinal microbiota metabolites have been reported to gain access to the bloodstream, accumulate in the skin and disrupt skin homeostasis.7

Although much of the research involving gut health effects on other organs and systems has been done in human medical research, the implications to animal production are clear. Maintaining good gut health is important not only for the absorption of nutrients, as efficiently as possible, but also for the general health of the animal.

Fortunately there are commercial products available that can help return conditions that favor a healthy microbiome, including prebotic, probiotics and postbiotics. All three of these categories of product either directly provide beneficial bacteria (probiotics) or helps support a gut environment that can support healthy bacteria (prebiotic and postbiotics).

1.    Katarzyna, S., et al. 2021. The role of microbiota-gut-brain axis in neuropsychiatric and neurological disorders. Pharmacological Research. Volume 172.

2.    Manderino,L., et al. 2017. Preliminary Evidence for an Association Between the Composition of the Gut Microbiome and Cognitive Function in Neurologically Healthy Older Adults. Journal of the International Neuropsychological Society, Volume 23, Issue 8, pp. 700 – 705  DOI:

3.    Kulbatsk, I., 2021. The Gut-Lung Axis: How Your Microbiome Might Be Linked to Respiratory Health. Health newsletter.

4.    Miller, B. and N. Bentancourt. 2014. J Dairy Science

5.    Escalda C, Botelho J, Mendes JJ, Machado V. 2021. Association of bacterial vaginosis with periodontitis in a cross-sectional American nationwide survey. Sci Rep 11(1):630. doi: 10.1038/s41598-020-79496-4.

6.    Qi X, Yun C, Pang Y, Qiao J. 2021. The impact of the gut microbiota on the reproductive and metabolic endocrine system. Gut Microbes. 13(1):1-21. doi: 10.1080/19490976.2021.1894070. PMID: 33722164.

7.    O'Neill CA, Monteleone G, McLaughlin JT, Paus R. 2016. The gut-skin axis in health and disease: A paradigm with therapeutic implications. Bioessays. 38(11):1167-1176.