The intestinal tract has a significant impact on a horse’s overall health. As such, equine researchers have focused much attention on the diversity of the gastrointestinal microbiome. These intestinal microbial residents affect local mucosal immunity, produce short-chain fatty acids (butyrate, propionate, and acetate) for energy, and develop tolerance to antigens. As a whole, these features help define a horse’s well-being. For instance, immune modulation within the intestines comprises 60% of a body’s immune function. A balanced microbiome and its bacterial byproducts contribute to metabolic health. And the gut-brain axis has significant impacts on a horse’s behavior.
Researchers have extended beyond the microbiome to look deeper at the gut microbiota’s metabolic impacts. While the diversity of bacterial species within a horse’s intestinal tract is important, each horse is an individual with differing bacterial constitutions. Further, these bacteria are in a constant state of change depending on the food ingested, the horse’s environment, medication given, season, and daily stressors.
No longer are researchers just looking at the collection of which individual bacteria—the microbiome—inhabit the gastrointestinal tract. Rather, they are looking at the products of microbial activity and subsequent function: This is referred to as the metabolome. These are smaller molecules that result from digestion of what a horse has consumed, including medications. Such molecules are important in cell signaling processes from chemicals they produce. The genes intestinal bacteria express are referred to as metatranscriptome, which describes the RNA and identifies which genes are “turned on.”
Another area of exploration currently underway is the “exfoliome,” which are the cells exfoliated from the intestinal lining as a normal process of epithelial renewal. By looking at mRNA within feces, researchers can determine which genes the epithelial cells lining the gastrointestinal tract express.
What the Microbiome Tells Us About NSAIDs’ Effects on the Equine GI Tract
Back in 2019, researchers examined the effect of non-steroidal anti-inflammatories (NSAIDs) on gastrointestinal injury in the horse and how they might mitigate these adverse effects through nutritional intervention with omega-3 fatty acids, antioxidants, L-glutamine, and prebiotics, probiotics, and postbiotics. In a 2024 study, researchers at the University of Georgia’s College of Veterinary Medicine analyzed the metabolome, microbiome, and exfoliome in horses with intestinal injury.1
This study involved 20 geldings split into two groups of 10 each—one group received oral phenylbutazone (4.4 mg/kg) once daily for nine days; the other group received a placebo paste. The research team collected feces and performed gastroscopy (with squamous scoring) on Days 0 and 10. Evaluation of microbiota DNA and rRNA, metabolomic (metabolites), and exfoliome RNA indicated that phenylbutazone incorporates into intestinal epithelial cells to cause mitochondrial injury and oxidative stress.
Under normal homeostatic conditions, the gastrointestinal mucosa is hypoxic to maintain an anaerobic environment that supports the many facultative or obligate anaerobes residing in the gut microbiota. Changes in the oxygen content from oxidative stress within the gut lumen alter the microbiota, metabolome, and exfoliome within the equine intestinal tract. Consequently, aerobic bacteria thrive where they wouldn’t normally, while certain obligate anaerobes—especially those responsible for butyrate production—diminish. These changes can potentially lead to inflammation and causative injury to the intestinal mucosa from oxidative stress and the occurrence of unfolded proteins along the endoplasmic reticulum. Such injury is reversible once the NSAID is eliminated. Appropriate supplementation (see recommendations in the next section) can further mitigate the adverse effects of NSAIDs.
‘Feeding the Equine Microbiome’ Can Help Prevent Gut Dysbiosis
The objective of “feeding” the microbiome is to nourish the favorable gut bacteria. Feeding in this context relies not just on nutrition but also exercise, medications, and a horse’s environment, daily routine, tasks, travel, competition, and stress.
Diet is a key element in feeding gut microbiota. In another recent study, researchers examined management strategies to prevent gut dysbiosis in horses.2
The authors posed the following dietary recommendations for optimal gastrointestinal health of the microbiome:
- At least 60% of a horse’s diet, and preferably more, should be high-quality forage. This promotes good function of the bacteria that ferment fibers to produce short-chain fatty acids such as butyrate and help maintain stable bacterial communities.
- Processed grains and concentrates should be limited as much as possible due to poor small intestinal digestion that causes them to spill over into the large colon where they ferment to cause acidosis and bacterial cell death.
Supplementation with pre-, pro-, and postbiotics can affect intestinal bacterial health. Here’s how:
- Prebiotics—psyllium, beet pulp, fructo-oligosaccharides from plants, and good-quality forage—are useful in that they are fiber-based and can provide nutrition to existing and beneficial gut microorganisms.
- Examples of probiotics include live organisms such as Saccharomyces (a yeast), Lactobacillus, Bifidobacterium, and Enterococcus, which are lactic-acid-producing bacteria. Yeast has probiotic functions for fiber digestion. Saccharomyces might provide the best benefits to microbiota modulation, based on study results.
- Concerningly, many probiotics lack reliable evidence for efficacy—the contents of a commercial bucket often do not contain the labeled organisms or amounts of those organisms within those products. Further, live organisms might not be able to sufficiently bypass the equine stomach’s acidity to colonize the large colon where they are needed; cecal fermentation might further diminish their viability.
- Postbiotics are metabolites and soluble byproducts like butyrate produced by gut microorganisms after feeding on fiber. Butyrate provides energy and nutrition to intestinal epithelial cells to further strengthen tight junctions between the cells. This optimizes the gut barrier’s integrity to prevent leaky gut syndrome.
Take-Home Message for Veterinarians: Researchers are currently examining metabolomic data from within the equine microbiome to identify biomarkers that could indicate leaky gut problems. This information might help veterinarians and nutritionists tailor a diet specific to a horse’s needs to favorably alter gut microbiome bacteria and affect the metabolome products’ activity and function. Specific diets—based on the above components—promote proliferation of favorable bacteria and production of their metabolites (metabolome). This can stabilize intestinal pH and other intestinal environmental factors important to ensuring a healthy microbial balance in the equine gut, which in turn contributes to the horse’s overall health.
References
- Whitfield-Cargile, C.M., Chung, H.C., Coleman, M.C. et al. Integrated analysis of gut metabolome, microbiome, and exfoliome data in an equine model of intestinal injury. Microbiome 12, 74 (2024). https://doi.org/10.1186/s40168-024-01785-1
- Boucher L, Leduc L, Leclère M, Costa MC. Current Understanding of Equine Gut Dysbiosis and Microbiota Manipulation Techniques: Comparison with Current Knowledge in Other Species. Animals 2024, 14, 758; https://doi.org/10.3390/ani14050758
Sentinel feed is formulated with gutWise Nutrient Release Technology to help promote a healthy gut microbiome. Click here to learn about its features and how it supports equine digestive health.
This article originally appeared in “Feeding for the Future: Nutrition Knowledge for the Modern Equine Practitioner,” brought to you by Sentinel Horse Feeds. You can download the complete issue here.
Related Reading
- Feeding Today’s Senior Horse
- Feeding Horses to Guard Against Gastric Ulcer Syndrome
- The Latest on Extruded Feeds for Horses
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