Leaky Gut in Horses – Symptoms, Causes, Treatment & Prevention

Leaky gut is a digestive issue is horses that occurs as a component of a broader gut health issue such as dysbiosis, inflammatory bowel disease, or gastric ulcers.

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. allergens, and pathogens can penetrate the gut wall. If they are not stopped by the local immune system, they will circulate through the blood to the rest of the body. This can lead to an aggressive immune response and may cause systemic inflammation; at which point the horse is obviously ill. ^[1]

Circulating bacterial toxins and the systemic immune response can directly trigger laminitis.

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 a symptom or component of a broader gut health issue. Leaky gut can be a component of:

• Dysbiosis (microbial imbalance involving overgrowth of a pathogen)
• Twisted gut
• Heat stroke
• Severe hindgut acidosis caused by extreme simple carbohydrate overload or experimental fructan overload

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 move past the level of the cells lining the intestine. There these substances encounter the local immune system – known as the gut-associated lymphoid tissue (GALT).

Foreign substances involved in leaky gut include the following pro-inflammatory molecules: pathogenic microorganisms such as E.coli (some strains), Salmonella and Clostridrium, bacterial endo- and exo-toxins, and antigens.

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]

If the GALT is overwhelmed, 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. The systemic inflammation that is triggered by microbes and other toxins entering the body can lead to endotoxemia (circulating bacterial toxins) or septicemia (circulating bacteria in the blood).

Mad About Horses

Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.

Apple Podcasts Spotify Youtube

Common Signs & Symptoms

Horses may experience loss of intestinal wall integrity in three general categories:

• Focal
• Diffuse and contained by the GALT
• Diffuse and not contained by the GALT

Focal loss of integrity

Focal loss of integrity is caused by parasites. This is likely a universal experience for horses as all horses are likely to be affected by internal parasites during their lifetime.

Common signs of parasite burden and associated leaky gut include:

• Weight loss
• Poor thrift
• Poor growth
• Colic
• Bloating

In addition, the GALT becomes exposed to a wide diversity of food antigens which can result in a true food allergy or intolerance. This might also generate antibodies which can cause false positives on allergy testing.

Other examples of conditions that involve the GALT and local tissues only include:

• Severe gastric ulcers (grade 3 or higher)
• Inflammatory bowel disease
• Right dorsal colitis
• Infections from pathogens such as Salmonella or Clostridia

In these cases, the inflammation is limited to the bowel. The horse will show varying degrees of colic. If the hindgut is involved they may also show diarrhea. There may be fever when there is infection.

Diffuse loss of integrity

The most severe grade is when the GALT is overwhelmed and a systemic (body-wide) inflammatory response occurs. This occurs with bowel deprived of normal blood supply, severe infectious diarrhea, heat exhaustion and in the acute phases of grain or experimental fructan overload.

As above, this is accompanied by endotoxemia and/or septicemia. Septicemia is most likely in individuals with poor immune responses, such as foals. Foals can develop joint infections (“joint ill”) with septicemia.

With both endotoxemia and septicemia, the horse is obviously ill and can show the following clinical signs:

• Fever
• Pale or infected mucus membranes
• Colic
• Dehydration
• Rapid heart rate
• Rapid respiratory rate
• Laminitis

If you notice these signs in your horse, contact your veterinarian immediately. In severe cases, shock and even death can result.

Diagnosis

In research studies, several techniques have been used to identify increased gut permeability.

Methods include measuring how well specific sugars that are not normally absorbed intact, such as sucrose or D-xylose, are absorbed after they are delivered directly into the stomach by nasogastric tube. ^[1]

Researchers have identified biomarkers of increased intestinal permeability. Biomarkers are factors in the blood that are suggestive of a condition but do not specifically identify the precise condition.

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

• Components of gut microbes – Lipopolysaccharide (LPS)
• Components of damaged intestinal cells – intestinal fatty acid binding protein (iFABP)
• D-lactate – the lactate produced by bacteria
• 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 malabsorption in inflammatory bowel disease involving the small intestine.

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 transportation and prolonged or strenuous exercise. ^[7][31]

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) Starch Overload

Starch from the diet is not fully digested in the stomach and small intestine. Diets high in starch can result in excess starch reaching the hindgut.

Hindgut pH

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

However, it requires a very high starch intake to reduce hindgut pH. The most likely scenario is a horse breaking into the feed room and rapidly consuming a large grain meal.

In research settings, grain intakes as high as 30% of the diet do not lower fecal pH. ^[10] In an experiment which measured pH inside the cecum directly, feeding as much as 8 g per kg of bodyweight daily, divided into two meals, did not change the pH. In that study, it took a diet of 57% cereal grains to produce evidence of a leaky gut barrier. ^[11]

Hindgut microbes

When starch from grains reaches the hindgut there is a shift to more organisms capable of fermenting starch and an increase in lactate production. Very large experimental starch overloads (16 g of pure cornstarch per kg of body weight) as a bolus produce severe acidosis and altered gut permeability. However, it is not clear at what feed intake level this would occur with commonly used feedstuffs.

Small intestine grain fermentation

Interestingly, it has been found that grain feeding results in spikes in bacterial lipopolysaccharide and inflammatory cytokines in the blood at times after feeding that correspond to when the meal is in the small intestine. ^[32]

Presumably this is because grain was being fermented by the microbes inhabiting the small intestine which are primarily geared towards fermentation of simple carbohydrates. ^[33] However, these effects are very short-lived and it is unclear what, if any, negative health effects they cause.

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]

Several scenarios of NSAID use can increase the risk of gut health issues, such as inducing right dorsal colitis which can lead to leaky gut. ^[34][35]. Avoid the following scenarios to reduce this risk:

• Chronic use of selective and non-selective NSAIDs
• Exceeding dosage recommendations
• Combining one or more NSAIDs
• Using NSAIDs in combination with omeprazole for gastric ulcer prevention

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

Prevention is always the best strategy to maintain digestive health and decrease the risk of leaky gut.

Below are seven 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 Energy-Dense Fibre or Fat

Horses in moderate to very heavy exercise that require extra calories should have their additional energy needs met primarily with added high-calorie fibre sources 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, soy hulls, and ground flax are highly digestible and provide energy in the form of fibre (beet pulp and soy hulls) or high-fat content (ground flax). You can also make tasty reduced-starch mashes by combining alfalfa or beet pulp with wheat bran or plain oats.

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 mechanisms.

For the sake of digestive tract stability and to maintain optimal fermentation of forages and high-fibre feeds, avoid feeding grains to provide extra calories. To balance a forage-based diet, vitamins and minerals should be provided by a low sugar/starch premix or pellet such as Mad Barn’s Omneity.

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.

Mad Barn’s Visceral+ is a pelleted gut health supplement that supports gastric and hindgut health. It also supports the immune system.

Visceral+

5 stars		83%
4 stars		5%
3 stars		4%
2 stars		3%
1 star		4%

424 Reviews

Learn More

• Our best-selling supplement
• Maintain stomach & hindgut health
• Supports the immune system
• 100% safe & natural

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.

Performance XL: Electrolytes

5 stars		93%
4 stars		2%
3 stars		2%
2 stars		2%
1 star		2%

59 Reviews

Learn More

• Scientifically formulated
• Optimal electrolyte balance
• Supports exercise performance
• Promote workout recovery

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.

Optimum Digestive Health

5 stars		80%
4 stars		6%
3 stars		6%
2 stars		4%
1 star		4%

185 Reviews

Learn More

• Prebiotics, probiotics & enzymes
• Support hindgut development
• Combats harmful toxins in feed
• Complete GI tract coverage

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.

w-3 Oil

5 stars		77%
4 stars		11%
3 stars		8%
2 stars		2%
1 star		2%

461 Reviews

Learn More

• Promotes joint comfort
• Helps to fight inflammation
• Skin & coat condition
• Palatable source of Omega-3's

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]

Summary

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. Certain bacterial toxins can also trigger laminitis.

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 an intestinal issue associated with altered gut permeability / leaky gut.

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