The horse’s gut microbiome has been shown to influence many aspects of equine health and well-being, including behavior, digestive health, and immune function. But why does the microbiome have such a powerful and wide-ranging impact? According to researchers, it is due to the microbiome’s many important connections to the nervous and immune systems.
Basics of the equine microbiome
The equine gut microbiome refers to the genetic material of the gastrointestinal microbiota—the diverse population of microorganisms living in the digestive tract—explains Liz Schatz, DVM, Senior Veterinary Affairs Specialist. These microorganisms include bacteria that break down fiber and protein and produce B vitamins and vitamin K; fungi that degrade fiber; protozoa and archaea that produce methane gas; as well as viruses and parasites.
Each horse’s microbiome is unique and influenced by many factors, including diet, age, climate, management, health conditions such as metabolic syndrome, stress, and medications. “Unfortunately, there are still significant gaps in our understanding of the equine microbiome. However, in human medicine, it has already been established that many diseases are linked to changes in the microbiome.”
The microbiome and equine health are closely connected
One of the most significant aspects of the gastrointestinal microbiome is its connection to the gut–brain axis.
“This means that the nervous, immune, and endocrine systems are all connected to the gut microbiome, and that changes in the digestive tract can have far-reaching effects,” Schatz said.
Changes in the microbiome may lead to behavioral changes such as anxiety, spookiness, and even stereotypies like cribbing or weaving. Mental stress can also affect the microbiota, creating a vicious cycle.
Effects on the horse’s immune system
“Seventy percent of the body’s immune system is located in the gastrointestinal tract, particularly in the lymphatic system, which is the immune system’s powerhouse,” Schatz said. “Anything that alters the digestive tract can affect the immune system and, consequently, the horse’s health.”
For example, horses with equine metabolic syndrome (EMS) have gut microbiomes that differ in microbial diversity compared to healthy horses.
“A depleted microbiome may contribute to the impaired immune response we see in horses with EMS, but much more research is needed to draw firm conclusions,” Schatz said.
Researchers are continually working to identify new microbial species in the digestive tract and to develop better methods for collecting samples from horses.
“We need a better understanding of the microbiome–gut–brain axis and the immune system’s role in specific diseases,” Schatz said. This could eventually make it possible to treat certain diseases by supporting the microbiome.
Substances that support the microbiome include:
Prebiotics: Ingredients or supplements that feed beneficial gut bacteria. Prebiotics are generally non-digestible fibers that promote the growth or activity of one or more bacterial strains in the large intestine. Their purpose is to support gut flora and overall health. Examples include inulin and dandelion root.
Probiotics: Live microorganisms naturally found in the gut, such as lactic acid bacteria (mainly Lactobacilli and Bifidobacteria), yeasts (Saccharomyces boulardii and Saccharomyces cerevisiae), or fungi. They occupy space in the gut that would otherwise be available to pathogenic bacteria, compete for nutrients, produce substances that inhibit harmful microbes, promote local immune responses, and alter the gut environment in ways that are unfavorable to pathogens.
Postbiotics: Metabolic by-products of bacteria—what remains after probiotic bacteria ferment prebiotics. This group includes vitamins such as vitamin K and B vitamins, short-chain fatty acids, peptides, enzymes, amino acids, and various polysaccharides. Gut bacteria and the brain communicate via postbiotics.
Examples of postbiotics and their functions:
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Short-chain fatty acids (e.g. butyrate, acetate, propionate):
Butyrate in particular serves as an energy source for epithelial cells in the intestinal lining and has been shown to promote intestinal integrity and mucus secretion while reducing inflammation. SCFAs have also been shown to support brain health. -
Neurotransmitters:
Gut bacteria influence brain and nervous system function via the gut–brain connection by producing neurotransmitters such as GABA, serotonin, dopamine, catecholamines, and acetylcholine. Bacteria in the Lactobacillus group are especially known for producing these compounds. -
Peptides:
Bacterial peptides have a wide range of functions. Of particular interest are antimicrobial and antiviral peptides that act against pathogens. Research is ongoing into whether bacteriocins could offer solutions to increasing antibiotic resistance. The postbiotic muramyl dipeptide has also been shown to improve insulin sensitivity. -
Exopolysaccharides (EPS):
Exopolysaccharides produced especially by lactic acid bacteria have been found to have anticarcinogenic, immunomodulatory, and antioxidant effects.
“More research is needed, so the best way to support your horse’s microbiota right now is to minimize stress, maximize time at pasture, provide high-quality and varied forage, and make all dietary changes slowly—including changes in hay,” Schatz said.
Source: The Horse.com
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