Leaky gut is a digestive issue that most commonly affects performance horses. It can increase the risk of colic and causes systemic inflammation.

It is said that 70% of the horse’s immune system resides in the gut. The horse’s gastrointestinal tract breaks down food and absorbs nutrients while blocking toxins and microbes from entering the body.

In horses affected by leaky gut, the contents of the gastrointestinal tract are not appropriately contained due to impaired intestinal barrier function.

Toxins and pathogens can penetrate the gut wall, circulating through the blood to the rest of the body. This can lead to an aggressive immune response and systemic inflammation. [1]

Chronic inflammation can increase the risk of other issues such as laminitis and insulin resistance.

Performance horses have a higher risk of this condition due to the effects of high-intensity exercise and feeding a high-starch diet.

Consult with your veterinarian if you suspect your horse has gut health issues. Submit your horse’s diet online for a complimentary evaluation by our nutritionists to optimize nutritional support of gut health.

What is Leaky Gut?

Equine leaky gut is typically not an isolated condition. It is an underlying symptom or component of a broader gut health issue such as dysbiosis (microbial imbalance) or hindgut acidosis.

Leaky gut is a general term used to describe impaired intestinal barrier function. Normally, the intestinal mucosal barrier blocks toxins and microbes from entering the body while enabling nutrients to be absorbed.

In horses affected by leaky gut, the gut wall is semi-permeable and allows foreign substances to enter the blood. This include the following pro-inflammatory molecules: pathogenic microorganisms such as E.coli, Salmonella and Clostridrium, toxins, and antigens.

These substances can trigger a strong immune response in the body. In particular, lipopolysaccharides (LPS) which are structural components of bacterial cell walls are one of the most pro-inflammatory molecules found in the gut.

Penetration of the gut wall by these substances can lead to local issues within the gut including inflammation of the intestinal tissue, chronic low-grade colic and diarrhea. [1][3]

The systemic inflammation that is triggered by microbes and other toxins entering the body can have a wide range of effects. Inflammation can lead to poor joint health, allergic responses, laminitis and insulin resistance. [1][2]

Common Signs & Symptoms

Horses affected by gut issues display a wide range of signs, including behavioural issues and digestive dysfunction.

It can be difficult to pinpoint the root cause as several gut issues show similar signs and symptoms. Horses with leaky gut may exhibit similar symptoms as horses affected by gastric ulcers and hindgut ulcers.

Common signs that your horse may have leaky gut syndrome include:

It is recommended to consult with your veterinarian to identify gut health issues and develop an appropriate treatment strategy.


There is no definitive way to diagnose leaky gut. In research studies, several techniques have been used to identify increased gut permeability.

Methods includes measuring how well specific sugars such as sucrose or D-xylose are absorbed after they are delivered directly into the stomach by nasogastric tube. [1]

However, these tests also identify gastric ulcers and inflammatory bowel disease and are not specific to leaky gut syndrome.

Researchers have identified biomarkers of increased intestinal permeability. Biomarkers are factors in the blood that are suggestive of a condition but do specifically identify the precise condition.

For leaky gut, suggested biomarkers that can be measured in blood include: [4][5][6]

  • Components of gut microbes – Lipopolysarrcharide (LPS)
  • Components of damaged intestinal cells – intestinal fatty acid binding protein (iFABP)
  • Indicators of an activated immune response – inflammatory cytokines (TNFa, interleukin-6), serum amyloid A (SAA)

Your veterinarian may choose to perform an oral glucose or xylose absorption test to measure how much of these are absorbed from the gut. This can indicate the severity of gut health conditions.

Common Causes

Leaky gut is multifactorial, meaning it can arise from a wide range of stressors including aspects of your horse’s diet and exercise program.

Below are the top five causes of leaky gut in horses.

1) High-intensity exercise

Horses, like other high-performance athletes, are susceptible to increased intestinal permeability due to prolonged and strenuous exercise. [7]

During exercise, blood flow is redirected to skeletal muscles and the extremities. [8] This results in decreased blood flow to the gut.

Extended periods of restricted blood flow to the digestive tract can increase the risk of intestinal cell damage, potentially increasing mucosal barrier permeability.

Furthermore, the high metabolic rate needed to support exercise produces heat. Extended periods where the core temperature exceeds 42°C (107°F)can result in exercise-induced hyperthermia.

This can damage cells that line the intestine which increases intestinal permeability and activates an immune response. [9]

Caution should be taken when exercising horses in hot and humid weather. Keep your horse hydrated, provide electrolytes, and cool your horse effectively after exercise to reduce the risk of intestinal barrier damage from exercise and heat stress.

2) High-Starch Diet

A diet high in starch can lead to hindgut acidosis which affects gut barrier function. Horses on grain-based diets or horses foraging on rich pasture grasses are at risk of starch overload.

When starch is high in the diet, it is not fully digested in the stomach and small intestine. This results in excess starch reaching the hindgut.

In the hindgut, starch fermentation produces lactic acid and volatile fatty acids. This lowers the gut pH, making the environment more acidic. [10][11]

Chronic fermentation of starch in the hindgut can kill off beneficial, fibre-digesting microbes and release toxins. Over time, this can impair nutrient absorption, damage the intestinal barrier, increase intestinal permeability, and result in an inflammatory response.

A high-starch diet should be avoided whenever possible to support gut health and minimize inflammatory conditions, including leaky gut.

3) Obesity

Obese horses may be at greater risk of gastrointestinal issues associated with increased gut permeability.

A recent study compared the intestinal permeability and inflammatory response of lean and obese horses. The obese horses had a higher level of bacterial components (LPS) in the blood compared to lean horses. [12]

In this study, lean horses had a body condition score of 4 or 5, whereas obese horses had a score of 7 to 9 on a 9-point scale.

It is recommended to assess your horse’s body condition on a regular basis. A change in body weight could indicate an underlying digestive issue.

Accurately identifying your horse as underweight or overweight is critical to making appropriate modifications to their feeding and management practices.

4) Use of Non-steroidal Anti-inflammatory drugs (NSAIDS)

Non-steroidal Anti-inflammatory drugs (NSAIDs) are routinely used in horses to manage pain and inflammation for several conditions including colic, laminitis, and lameness. [13]

NSAIDs are effective for reducing inflammation and the pain associated with swelling or fever. However, long-term or excessive use can impair intestinal barrier function. [13]

NSAIDs work by blocking the enzymes cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) which are involved in making prostaglandins. Prostaglandins are hormones that are important components of an immune response.

COX-1 is also involved in making prostaglandins that protect the stomach and intestinal lining. Use of NSAIDs that inhibit this enzyme can damage the intestinal lining.

This is of particular concern with traditional NSAIDs such as bute (phenylbutazone) and banamine (flunixin meglumine), which are non-selective COX inhibitors. [13]

Selective COX-2 inhibiting drugs have been developed for both human and animal medicine. Deracoxib and firocoxib (Equioxx, Previcox) and have less of an impact on the digestive tract. [13]

A study in horses found that phenylbutazone (non-selective COX inhibitor) significantly increased intestinal permeability when compared to meloxicam (COX-2 selective). [14]

Chronic use of NSAIDs increases the risk of gut health issues, including leaky gut. It is best to check with your veterinarian before administering any medications and always follow the recommended dosage protocol.

5) Antibiotic Use

Antibiotics are sometimes required to fight bacterial infections, but they also kill off beneficial microbes and can alter gut microbial populations. This may lead to dysbiosis and digestive dysfunction.

The horse’s intestinal microbiome plays a role in fibre digestion, which is the main source of energy production in the horse’s diet. [15]

It can take time for a healthy microbiome to re-establish itself following the use of antibiotics. This disruption in the hindgut microbial environment is associated with increased intestinal permeability. [16]

Antibiotics should only be used under the guidance of a veterinarian for a specific purpose and defined time period. Consider using probiotics or yeast supplements to support gut health in horses being treated with antibiotics.

7 Ways to Prevent Leaky Gut in your Horse

Digestive issues such as leaky gut, ulcers or free fecal water syndrome are often difficult to resolve once they are present. Prevention is always the best strategy to maintain digestive health.

Below are 7 key principles to support your horse’s gut health and minimize the risk of leaky gut:

1) Feed A Forage-First diet

Supporting gut health begins with feeding a well-balanced forage-first diet that meets the horse’s energy and protein needs.

Hay and/or pasture should make up the majority of your horse’s feeing plan. For horses in maintenance or light to moderate exercise, moderate-quality hay and pasture are usually sufficient to meet energy and protein requirements.

Horses should be allowed to forage for at least 16 hours per day with no more than 3-4 hours without access to forage.

It is important to choose hay that matches your horse’s needs. Proper hay selection is the first step to supporting digestive health.

High-quality hay with higher protein and energy should be used for performance horses, whereas low-quality hay is appropriate for horses at maintenance or with a high body condition score.

2) Provide Additional Calories as Fat

Horses in moderate to very heavy exercise that require extra calories should have their additional energy needs met primarily with added fat or oils.

Oils such as flax, soybean, camelina or canola oil provide a dense calorie source without relying on added grains that have a high starch content.

Alternatively, beet pulp, rice bran, and ground flax are highly digestible and provide energy in the form of fibre (beet pulp) or high-fat content (rice bran and ground flax).

When adding oils to the diet, select fat sources that provide an appropriate balance of omega-3 to omega-6 essential fatty acids to support anti-inflammatory benefits.

3) Support the Intestinal Lining

Vitamins and minerals are required by all cells of the body to perform necessary functions including making proteins, maintaining healthy cell membranes and enabling cell turnover.

The gut in particular has a high rate of cell turnover. Individual cells that make up the intestinal lining only survive for 3 days before they are sloughed off and replaced by new cells.

The gastrointestinal lining is a very metabolically active tissue that requires key nutrients such as zinc, copper, selenium and vitamin E to support antioxidant status.

It also has a high requirement for amino acids to make proteins and act as an energy source.

The amino acid glutamine is a major energy source for intestinal cells. [17] Equine gut health supplements often include glutamine to support intestinal barrier function and help maintain gut integrity.

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4) Reduce the risk of heat stress

Heat stress can originate from excessive, prolonged exercise, hot, humid conditions and inadequate hydration.

Exercise naturally decreases blood flow to the gut which negatively affects intestinal cell viability. This is exacerbated by the increase in core temperature caused by exercise, especially in hot, humid conditions when sweating is less effective.

Whenever possible, exercise your horse in cooler temperatures and in low humidity. This will make sweating more effective and help the horse stay cooler during exercise.

It is crucial to support hydration before and after exercise. Feeding loose salt on a daily basis helps stimulate thirst and promote water intake.

On days when your horse is sweating due to exercise or exposure to heat, electrolytes such as sodium, potassium and magnesium should be replaced with an electrolyte supplement.

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Following exercise, help your horse cool down to minimize heat stress. Recent research has shown that constant contact with cold water is more effective at cooling horses after exercise than cold water with scraping.

Constant cold water for 6 minutes decreases core body temperature and may help prevent heat illness after exercise. [30]

5) Responsible NSAID and antibiotic use

Only use prescription NSAIDs and antibiotics under veterinary direction. Follow dosing guidelines closely and avoid long-term use where possible.

This will ensure that the most appropriate pharmaceutical is used to treat or manage illness and pain while minimizing side effects.

Using pharmaceuticals not as directed by veterinarians increases the risk of long-term side effects including antibiotic resistance and Right Dorsal Colitis.

6) Supplement with Prebiotics and Probiotics

Prebiotics and probiotics are common supplements used to support the hindgut microbiome in horses.

Prebiotics are types of fibre that act as a fuel source for beneficial hindgut microbes. Probiotics are the beneficial living microbes (bacteria, yeast, fungi) that digest fibre and support immune function.

While research is limited on the effects of prebiotics and probiotics on intestinal permeability in horses, research from humans and other species demonstrates a benefit for intestinal barrier function.

There is equine research to support the therapeutic use of prebiotics and probiotics for reducing “bad” bacteria and supporting beneficial microbes. [18][19][20]

Common probiotic species include bacteria (Bifidobacterium and Lactobacillus), and yeast (Saccharomyces cerevisiae). [18][19][20]

Common prebiotics include oligosaccharides (long chains of sugar molecules) such as fructo-oligosaccharides (FOS) which are digested by beneficial microbes and support the growth of these microbes in the gut. [18][21][22]

Mannan-oligosaccharides (MOS) are derived from yeast and are typically considered prebiotics. However, they work mainly by binding toxins to prevent them from being absorbed into the body.

More research is needed to determine the specific effects of prebiotic and probiotic supplementation on intestinal barrier permeability in horses.

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7) Provide anti-inflammatory support

Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs) that are essential for supporting anti-inflammatory mechanisms in the body.

Horses typically receive omega-3s in the form of ALA (alpha linolenic acid) from fresh forages. This plant-based omega-3 must first be converted to the active forms of DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) to exert an anti-inflammatory benefit in the body.

However, the conversion process of ALA to DHA and EPA is inefficient and feeding DHA and EPA directly promotes a greater anti-inflammatory response. [23][24]

Research in other animals demonstrates the benefits of DHA for supporting gut barrier function. In mice with experimentally induced colitis, providing a diet rich in omega-3 fatty acids had a protective effect on the intestinal barrier. [25]

EPA and DHA were shown to alleviate heatstroke damage, reduce intestinal permeability, and plasma endotoxin levels in rats. [26].

In pigs, fish oil (rich in DHA) was also found to improve intestinal barrier integrity by blocking inflammatory signaling pathways. [27]

EPA and DHA also improved intestinal cell integrity when challenged with a common mycotoxin. [28]

Mad Barn’s w-3 Oil is an essential fatty acid supplement that is high in DHA. It is an effective cool energy source for horses and can help support digestive health as well as exercise performance.

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Spirulina is another supplement that may support anti-inflammatory and anti-oxidant processes in the body. In one study, intestinal cells from horses with equine metabolic syndrome were treated with spirulina and experienced reduced inflammation and oxidative stress. [29]


Leaky gut is a digestive issue that results in inflammation in the gut as well as absorption of toxins and other factors that trigger an immune response in the body. This contributes to chronic inflammation which underlies common equine issues such as laminitis, insulin resistance and joint problems.

Preventing gut health issues should be a major priority for any horse owner. Reducing heat stress, supporting hydration and appropriately using NSAIDs and antibiotics will help to minimize the risk of leaky gut.

Your horse’s nutrition program can also support gut health by feeding a forage-based diet with low starch content and using fats for additional energy. Meeting micronutrient requirements is also critical for supporting healthy cell turnover in the intestinal lining.

Supplementation with prebiotics, probiotics and anti-inflammatory fatty acids is also beneficial for horses identified as having leaky gut.

For help with formulating a gut-healthy feeding plan, submit your horse’s diet for review by our equine nutritionists.

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  2. Chelakkot, C. et al. Mechanisms regulating intestinal barrier integrity and its pathological implications. Exp Mol Med. 2018.
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  4. Gilani, S. et al. New biomarkers for intestinal permeability induced by lipopolysaccharide in chickens. Anim Prod Sci. 2016.
  5. Niewold, T.A. et al. Plasma intestinal fatty acid binding protein (I-FABP) concentrations increase following intestinal ischemia in pigs. Res Vet Sci. 2004.
  6. Hulten, C. et al. The acute phase protein serum amyloid A (SAA) as an inflammatory marker in equine influenza virus infection. Acta Vet Scand. 1999.
  7. Costa, R.J.S. et al. Systematic review: exercise-induced gastrointestinal syndrome—implications for health and intestinal disease . Aliment Pharmacol Ther. 2017.
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  11. Destrez, A. et al. Changes of the hindgut microbiota due to high-starch diet can be associated with behavioral stress response in horses. Physiol Behav. 2015.
  12. Kopper, J.J. et al. Effect of body condition on intestinal permeability in horses. Am J Vet Res. 2019.
  13. Marshall, J.F. and Blikslager, A.T. The effect of nonsteroidal anti-inflammatory drugs on the equine intestine. Equine Vet J Suppl. 2011.
  14. D’Arcy-Moskwa, E. et al. Effects of meloxicam and phenylbutazone on equine gastric mucosal permeability. J Vet Intern Med. 2012.
  15. Costa, M.C. et al. Changes in the equine fecal microbiota associated with the use of systemic antimicrobial drugs. BMC Vet Res. 2015.
  16. Tulstrup, M.V.L. et al. Antibiotic Treatment Affects Intestinal Permeability and Gut Microbial Composition in Wistar Rats Dependent on Antibiotic Class. PLoS One. 2015.
  17. Duckworth, D.H. et al. Arteriovenous differences for glutamine in the equine gastrointestinal tract. Am J Vet Res. 1992.
  18. Wasilewski, A. et al. Beneficial Effects of Probiotics, Prebiotics, Synbiotics, and Psychobiotics in Inflammatory Bowel Disease. Inflamm Bowel Dis. 2015.
  19. Desrochers, A.M. et al. Efficacy of Saccharomyces boulardii for treatment of horses with acute enterocolitis. J Am Vet Med Assoc. 2005.
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  21. Gurbuz, E. et al. Effects of supplemental fructo-oligosaccharide and mannan-oligosaccharide on nutrient digestibilities, volatile fatty acid concentrations, and immune function in horses. Turk J Vet Anim Sci. 2010.
  22. Respondek, F. et al. Effects of dietary short-chain fructooligosaccharides on the intestinal microflora of horses subjected to a sudden change in diet. J Anim Sci. 2008.
  23. Barbalho, S.M. et al. Polyunsaturated fatty acids, inflammatory processes and inflammatory bowel diseases. Ann Gastroenterol. 2016.
  24. Calder, P.C. Fatty acids and inflammation: The cutting edge between food and pharma. European J Pharmacol. 2011.
  25. Whiting, C.V. et al. Dietary n-3 Polyunsaturated Fatty Acids Reduce Disease and Colonic Proinflammatory Cytokines in a Mouse Model of Colitis. Inflamm Bowel Dis. 2005.
  26. Xiao, G. et al. Eicosapentaenoic acid enhances heatstroke-impaired intestinal epithelial barrier function in rats. Shock. 2015.
  27. Liu, Y. et al. Fish Oil Enhances Intestinal Integrity and Inhibits TLR4 and NOD2 Signaling Pathways in Weaned Pigs after LPS Challenge. J Nutr. 2012.
  28. Xiao, K. et al. EPA and DHA attenuate deoxynivalenol-induced intestinal porcine epithelial cell injury and protect barrier function integrity by inhibiting necroptosis signaling pathway. FASEB J. 2020.
  29. Nawrocka, D. et al. Spirulina platensis Improves Mitochondrial Function Impaired by Elevated Oxidative Stress in Adipose-Derived Mesenchymal Stromal Cells (ASCs) and Intestinal Epithelial Cells (IECs), and Enhances Insulin Sensitivity in Equine Metabolic Syndrome (EMS) Horses. Mar Drugs. 2017.
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