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Maintaining your horse’s digestive health is integral to maintaining their overall health.
Digestive issues such as colic, ulcers, and hindgut acidosis are some of the most commonly diagnosed health conditions in horses.
Furthermore, without a healthy gut, horses could experience secondary nutrient deficiencies, impaired energy metabolism, lower feed efficiency, and could be at higher risk of pathogenic diseases.
Unsurprisingly, nutrition is a major component of optimizing your horse’s stomach and hindgut health. How and what you feed your horse can help to maintain a healthy gut environment and support the microbiome.
Looking for the best digestive health supplements for your horse? Several nutritional supplements have been investigated in horses and have demonstrated efficacy for maintaining a healthy gut.
In this article, we will review the scientific data behind fifteen popular ingredients used to support digestion and gut function in horses.
We will discuss the potential benefits of these supplements and their efficacy according to the available research and clinical trials.
Overview of Equine Digestive Health
The digestive system of the horse is unique compared to other mammals. Horses are non-ruminant herbivores, meaning they naturally only eat plants and have a single-compartment stomach.
The stomach and small intestine of the horse function similarly to that of humans. The hindgut consists of the cecum and colon, in which the cecum and large colon are similar to the rumen in cattle and other ruminants.
Horses are also hindgut fermenters. This means that they rely heavily on fermentation processes in the hindgut to derive energy from the forage they consume.
Microbes in the hindgut are responsible for fermentation of cellulose and other plant fibres to produce volatile fatty acids (VFAs). These fatty acids then get absorbed in the cecum and large intestine and used for energy, supplying approximately 40% of the horse’s caloric energy.
Steps of Digestion in Horses
Digestion of food involves the following steps in horses: [1]
1) Mechanical Digestion (Chewing)
The breakdown of food starts with chewing or mastication in the mouth. While often overlooked, chewing is important because it breaks food down into smaller pieces.
This increases the surface area of the feed for digestive enzymes to further break down these particles.
Saliva is also produced when chewing, which promotes gastric health by acting as an acid buffer in the stomach.
Horses that have dental issues or missing teeth will often need to be on a modified diet because they cannot chew their food well.
2) Chemical Digestion (The Stomach)
Food enters the stomach and is further broken down by digestive enzymes, microbes, and gastric acid.
The naturally acidic environment of the stomach plays a key role in the immune system. It can prevent infectious or harmful microorganisms from entering the rest of the digestive system.
The predominant stomach acid is hydrochloric acid and horses can produce 16 gallons per day of this acid.
It is continuously produced by stomach cells even when there is no food present in the stomach, which, incidentally, is why horses with intermittent feeding schedules are at higher risk of ulcers.
3) Nutrient Absorption (The Small Intestine)
When food leaves the stomach, it enters the small intestine. Enzymes continue to break down the food even more.
Importantly, the small intestine is the major location for the absorption of nutrients from starches, proteins and fat in the diet.
4) Hindgut Fermentation (Cecum and Colon)
The vast microbial population in the hindgut is primarily responsible for breaking down fibre from hay, pasture and other forages.
This produces large amounts of volatile fatty acids (VFA), which are the major energy source for the horse.
Leftover, or undigested, food moves through the rest of the colon where water is absorbed and feces is formed and excreted.
How to Support your Horse’s Digestive System
Horses are known for having particularly sensitive digestive systems. They are very susceptible to digestive upsets, particularly when anything in their diet or routine changes.
If you are reading this article, your horse is likely experiencing one of the following complaints which can be linked to gut health:
- Diarrhea
- Free Fecal Water Syndrome
- Gastric Ulcers
- Hindgut Ulcers
- Lack of Appetite
- Flatulence (Gas) or Bloating
- Constipation
- Lethargy or Weakness
- Girthiness or Abdominal Sensitivity
- Colic
- Colitis or IBD
- Weight Loss or Poor Body Condition
- Dysbiosis
- Immune Dysfunction
- Poor Skin or Coat Quality
- Poor Hoof Growth
- Irritable Mood
Horses with any of these digestive complaints can benefit from dietary supplements. Improving your horse’s gut health can not only impact digestion and nutrient absorption but also immune function, performance, comfort and overall well-being. [19]
Additional benefits of a well-functioning digestive system include:
- Improved synthesis of vitamins and key nutrients
- Improved pathogen resistance
- Protection against toxins
- Better gut-barrier function
- Influencing the gut-brain connection to promote positive behaviour and mood
- Improved body condition
- Increased resistance to stress
Before adding supplements to your horse’s feeding program, we recommend consulting with an equine nutritionists. You can submit your horse’s diet for analysis online and our nutritionists can provide a complimentary review.
Top 15 Supplements for Your Horse’s Digestive Health
1) Visceral+
Visceral+ is Mad Barn’s gold-standard digestive health supplement. It is designed to support gastric and hindgut health and immune function.
Ingredients
- Bio-Mos™
- Yea-Sacc1026™ – Saccharomyces cerevisiae yeast
- 20 billion CFUs of probiotics
- Lecithin
- Docosahexaenoic Acid (DHA) – an omega-3 fatty acid
- Methionine
- Kelp meal
- Magnesium
- Choline
- Marshmallow Root Extract
- Meadowsweet
- Slippery Elm Bark
- Glutamine
Targets for Digestive Health
Visceral+ supports the stomach, hindgut and immune system.
2) Optimum Digestive Health
For horses with hindgut issues or horses that need help keeping weight on, Optimum Digestive Health is the recommended choice.
Ingredients
- Digestive Enzymes to help break down feed components in the small intestine
- Saccharomyces cerevisiae species of yeast which has been clinically shown to promote digestive health in a variety of animals
- Kelp meal for its rich amino acid, vitamin, and mineral profiles
- Dietary Escape Microbial Proteins as a high-quality protein source that will be digested in the small intestine
- Prebiotics such as beta-glucans which feed the beneficial microbes along the digestive tract
- Mannan oligosaccharides which bind to and neutralize toxins that may be present in feed
- Magnesium, sodium, and potassium which are important electrolytes that support gut motility
- Peppermint for its soothing effects on the digestive system
- Mad Barn’s 5-Strain Probiotic to balance the gut microflora and support fibre digestion in the hindgut
Targets for Digestive Health
Optiumum Digestive Health supports hindgut health and immune function.
3) Yeast
Yeast is a type of fungus that is commonly used as a probiotic to support hindgut function in horses.
While there are many different species of yeast, [5] Saccharomyces cerevisiae is most commonly used in horses.
Yeast cultures can promote nutrient absorption from the diet and improve feed efficiency. They are commonly fed to horses that are hard keepers, senior horses and performance horses with greater nutrient demands.
Yeast may also support immune function. The cell walls of yeast are used as toxin binders in equine supplements.
Targets for Digestive Health
- Fibre fermentation by the hindgut microbiome
- Immune response
Efficacy of Yeast for Digestive Health
Research has demonstrated that live yeast cultures in equine diets survive passage through the acidic stomach and reach the hindgut intact. [5]
Fibre Digestion
Yeast supplements can support fibre digestion in the hindgut, which supplies critical nutrients and caloric energy to your horse.
High-starch diets are one of the main culprits for impaired fibre digestion and hindgut dysfunction in horses.
When horses are fed excess grain, high levels of starch reach the hindgut where microbes convert it to lactic acid.
This lowers the pH (increases the acidity) of the hindgut which negatively affects fibre digesting microbes, potentially leading to dysbiosis.
In one study, the negative effects of a high-starch diet were mitigated by adding yeast to the diet. [6]
Horses in training on high-starch diets had improved fibre digestibility when yeast was included in the diet. [2] This improved overall digestible energy in the diet and could support athletic performance. [12]
Yeast may also benefit horses given low-quality hay by helping them extract more energy and nutrients from the feed. Horses fed low-quality hay and supplemented with yeast showed greater fibre digestibility compared to horses fed low-quality hay without a yeast supplement. [3]
Protein Digestion
Yeast has been shown to increase the nutritional value of low-quality hay by improving protein digestibility. [3]
Yearlings fed live yeast cultures also had increased microbial production of amino acids. [4]
It’s unclear whether these amino acids can be absorbed from the hindgut. However, they can be consumed by other microbes to support hindgut digestive function.
This can also reduce nitrogen excretion in urine to decrease the environmental footprint of horses.
Digestive Dysfunction
Horses with digestive issues such as colitis may benefit from yeast supplements.
Researchers fed horses diagnosed with acute colitis a yeast supplement at either 25 g or 50 g for ten days. At the end of the study, horses in both groups showed decreased severity of colitis and a shorter duration of gastrointestinal disease. [7]
Yeast has been shown to benefit immune function in other species. In pigs, yeast appears to support the immune system and overall health by improving gut barrier function. This prevents bacteria and other pathogens from entering the body. [8]
In a recent review study, yeast was found to improve immune function in livestock through a variety of mechanisms. [9] More research is needed to understand how yeast influence the immune system in horses.
You can read more about the known benefits of yeast in horses in our article: 7 Research-Backed Benefits of Yeast for Horses.
THE VERDICT: Significant evidence of efficacy for improved nutrient digestibility in the hindgut of horses. More research is required for immune-modulating effects.
4) Digestive Enzymes
Digestive enzymes are involved in enzymatic digestion of nutrients in the gut. Different enzymes break down different dietary components into fractions that can be absorbed.
These chemicals are naturally present in saliva, the stomach, the small intestine and produced by microbes in the hindgut.
Popular digestive enzyme supplements for horses can include one or more of the following enzymes:
- Amylase: Digestion of starch into glucose and maltose
- Protease: Breaks down proteins into amino acids, or smaller peptides
- Lipase: Involved in the breakdown of fats
- Phytase: Breaks down phytate to make phosphorus available for absorption
- Cellulase: Breaks down cellulose – a fibre component of plant cell walls
- Xylanase: Digestion of hemicellulose – a fibre component of plant cell walls
Mad Barn’s Optimum Digestive Health contains Allzyme SSF, a proprietary formulation of digestive enzymes. This blend is commonly used in livestock to support nutrient digestion and absorption in the intestines.
Targets for Digestive Health
- Increase digestion and breakdown of food to enhance nutrient absorption
- Support hindgut fibre digestion
- Enhance phosphorus absorption
Efficacy
The efficacy of digestive enzymes varies depending on the type and combination of enzymes used as well as the content of the diet.
In 2003, a study evaluated the effects of xylanase and cellulase on fibre digestion. These are enzymes that microbes in the hindgut produce to break down fibre.
Yearling geldings were fed Bermudagrass hay along with one of four additional feeds: textured sweet feed, pelleted concentrate, whole oats, or alfalfa cubes. Horses received either the supplemental xylanase and cellulase or no digestive enzymes for 7 days. [13]
The researchers observed improvements in fibre digestion when enzymes were added to the sweet feed and whole oat diets but not in other diets.
It should be noted that another study found no improvements in fibre digestibility when cellulase was given to horses fed grass hay with whole oats. [14] More research is required to understand the variability in results.
Effects on the Microbiome
Digestive enzyme supplementation may impact microbial function in the hindgut.
Researchers at North Carolina State University assessed the effects of multiple digestive enzymes on cell culture of microbes taken from the cecum of horses. [15]
The purpose of this study was to mimic high-carbohydrate diets in which large amounts of starch reach the hindgut.
The researchers hypothesized that adding high levels of lipase, protease, cellulase, and amylase would support fermentation by microbes taken from the hindgut.
The results demonstrated higher production of volatile fatty acids when digestive enzymes were added. This could theoretically lower pH and negatively affect fibre digesting microbes in the hindgut, but the researchers noted that the pH was not low enough to induce acidic stress.
More research on the impact that digestive enzymes could have on the microbiome is warranted.
Mineral Absorption
Digestive enzymes may enhance the absorption of minerals like phosphorus from the gut. Phosphorus is naturally found in plant material bound within phytate making it unavailable for absorption.
Adding phytase to the diet increases phosphorus digestibility and decreases its excretion in feces. This is important for horses with impaired phosphorus digestion such as senior horses, horses that have had previous colic resection surgery, and horses with chronic intestinal damage from a high worm load. [16]
THE VERDICT: Some evidence of improved digestive function in horses. More research is required.
5) Kelp Meal
Kelp is a type of seaweed and is often considered a nutritional “superfood”. It is used to improve digestive health in livestock.
It contains a number of valuable nutrients such as essential amino acids, fatty acids, fibre, and many vitamins and minerals. [20]
Kelp is also a source of prebiotic fibre, which can help promote the growth of probiotic bacteria.
Targets for Digestive Health
- Immune response
- Anti-inflammatory and antioxidant effects
- Microbial environment
- Digestive tract integrity
Efficacy
Kelp meal is a nutritionally dense feed additive for horses. With regards to digestive function, the high-quality protein content and prebiotic components are most relevant.
Amino acids are the building blocks of protein. Kelp meal supplies nine essential amino acids and 11 non-essential amino acids. [20]
Proteins build and repair tissues throughout the body, including in the digestive tract where cells have a high turnover rate. [1]
Cells lining the digestive tract have some of the shortest lifespans of any cells in the body, surviving for 3 days on average.
New cells are constantly developing to replace old cells that die off. This process requires a lot of nutrients – including amino acids – to remodel stem cells into functional cells of the digestive tract.
Supporting cell turnover is especially important when there are digestive issues that damage the intestinal lining.
Horses experiencing irritable bowel syndrome, inflammatory bowel disease, leaky gut, or hindgut ulcers need the right balance of amino acids to support tissue repair.
Prebiotic Effects
Kelp meal is high in polysaccharides which acts as a prebiotic to feed beneficial microbes in the gut and decrease levels of harmful microbes.
Seaweed supplementation was found to decrease E. coli populations in the stomach and intestine of pigs and increase beneficial microbes including Lactobacilli. [21]
More research is needed to study the prebiotic effect of kelp meal in horses.
THE VERDICT: Significant evidence for digestive health in other species. More research is needed in horses.
6) Probiotics
No list of digestive health supplements would be complete without discussing probiotics.
Probiotic supplements contain live microorganisms that are fed orally to the horse for a health-promoting effect. [22] These “good” bacteria support digestion and immune function.
Horse owners often think of the hindgut when discussing the microbiome, but bacteria actually exist throughout the digestive system.
A healthy microbiome requires a delicate balance between so-called good and bad bacteria. Pathogenic bacteria, such as E.coli, are considered “bad” because they produce toxins that kill good bacteria.
Diet, environment, stress, illness, medications, and many other factors can tip the scale towards dysbiosis, or a destabilized microbial environment. Probiotic supplements can help to maintain a healthy microbial balance throughout the digestive tract.
Targets for Digestive Health
- Nutrient digestibility and absorption
- Microbial environment
- Immune response
- Synthesis of proteins or enzymes
Not all probiotic supplements work equally well. There are many species and strains of probiotics to consider, as well as different supplement formulations to preserve the viability of the microbes.
Some of the most researched species of probitoics include:
- Lactobacillus acidophilus: This bacteria species is known for producing lactic acid
- Lactobacillus fermentum: Another lactic acid producing bacteria that is found naturally in the horse’s gut
- Lactobacillus casei: Thought to aid in immune response, L. casei is often supplemented to reduce infections in the intestine and to promote regular bowel movements
- Lactobacillus plantarum: Also a lactic acid producing bacteria. It may prevent the growth of harmful bacteria by competing with them for the same food sources
- Enteroccocus faecium: The most prevalent species of probiotic bacteria in horses
Mad Barn’s Optimum Probiotic contains the five strains mentioned above. Each serving provides 20 billion viable CFUs to ensure adequate numbers reach the hindgut.
The Optimum Probiotic 5-strain blend has been scientifically formulated to support your horse’s digestive health. It works to balance the horse’s gut microflora, improve nutrient assimilation and support the immune system.
Efficacy of Probiotics for Digestive Health
Probiotics may exert an anti-inflammatory effect on the digestive tract. In cell culture studies, probiotics have been shown to inhibit certain inflammatory mediators. [22]
Probiotic have also been shown to improve mucous integrity and immunity in multiple cell culture studies. [22]
Different species of probiotic bacteria produce lactic acid, fatty acids, acetic acid, and butyric acid. These compounds maintain a healthy pH throughout the gut and may prevent the growth of harmful bacteria, such as Clostridium.
In one study using cell cultures, the addition of L. fermentum did not inhibit Clostridium growth. But it did prevent the Clostridium bacteria from producing harmful toxins. [23]
In another study, researchers used an in vitro design to mimic the fermentation process of the gut. Using fecal samples from Azteca horses, they investigated the effects of a probiotic supplement containing Lactobacillus strains on fibre digestion. [24]
The researchers found that the probiotic resulted in a slightly lower pH and higher metabolizable energy, demonstrating increased fibre digestion. Higher dosages of probiotics were correlated with greater fibre digestion. [24]
In vitro studies are important for informing our understanding of how supplements such as probiotics work. However, clinical trials in horses are required to validate efficacy.
Clinical Trials
Clinical trials investigating the supplementation of probiotics in horses are difficult to compare. Doses and probiotic strains differ between studies. The duration of supplementation also varies significantly.
One study in foals investigated supplementation with a blend of Lactobacillus strains. The researchers found that foals supplemented with the probiotic had less diarrhea. [25]
Another study in horses hospitalized for colic did not find any differences in diarrhea incidence or shedding of Salmonella for horses supplemented with Lactobacillus. [26]
Read more about the benefits of probiotics for horses in our article: 6 Science-Backed Benefits of Probiotics for Horses.
THE VERDICT: Some evidence of efficacy in horses. However, evidence varies across different probiotic strains and blends. More research is required.
7) Spirulina
Spirulina is a type of blue-green algae that grows in fresh water lakes.
Athrospira platensis and Athrospira maxima are the two species commonly used in dietary supplements. They are rich in proteins, essential fatty acids, vitamins, and minerals.
Spirulina is associated with improved immune function, anti-inflammatory effect, and antioxidant protection.
Targets for Digestive Health
- Immune response
- Anti-inflammatory and antioxidant
- Nutrient digestibility
- Microbial environment
Efficacy
Spirulina modulates many immune response pathways in the body. It may support immune functions specific to the digestive tract.
Inflammation in the gut weakens the intestinal barrier, resulting in the development of a leaky gut. This can allow bacterial products to enter the bloodstream from the gut.
The ensuing immune response is a contributing factor for laminitis, particularly in horses with equine metabolic syndrome (EMS).
In an in vitro study, intestinal cells were taken from horses diagnosed with EMS and treated with Spirulina. The researchers found that Spirulina reduced inflammation and oxidative stress in intestinal cells. [10]
EMS horses fed spirulina also had improved insulin sensitivity and weight loss.
In another study, healthy horses were fed 500 g of feed containing Spirulina daily for three months. These horses had lower fasting insulin levels and improved glucose tolerance. [10]
Gastric Mucosa and Microbiome
Spirulina may also support the gastric mucosa and help maintain the structural integrity of the gastrointestinal tract.
A healthy mucous lining can prevent intestinal damage from bacteria and pathogens, and reduce the risk of ulcers.
This could have benefits for nutrient absorption, as demonstrated in pigs. Spirulina supplementation in swine was found to improve digestive tract structure and function. [11]
In other animals, it has been shown to confer benefits on the gut microbiome, but this has not been directly studied in horses. [17][18]
Spirulina is safe for equine consumption and exhibits anti-inflammatory effects in conditions ranging from EMS to recurrent respiratory issues such as allergies, heaves and inflammatory airway disease.
Read more about the top 9 Research-Backed Benefits of Spirulina for Horses here.
THE VERDICT: Evidence for digestive health in other species. Some in vitro evidence in horses, but further studies are required.
8) Salt and Electrolytes
Feeding plain loose salt to your horse is the cheapest way you can support gut function. Most forage-based diets are deficient in sodium which can contribute to poor appetite, lethargy and poor skin quality.
Feeding your horse adequate salt stimulates thirst and encourages water intake. Proper hydration keeps feed moving through the gut and helps decrease the risk of colic in horses.
We recommend feeding two tablespoons of salt per day and ensuring free-choice loose salt and fresh water are consistently available to your horse. This will support gut motility and a healthy digestive tract.
Electrolytes
In addition to sodium, your horse requires the following electrolytes in their diet:
- Potassium
- Calcium
- Chloride
- Magnesium
Sodium, potassium, calcium, and magnesium are cations (positively charged ions), whereas chloride is an anion (negatively charged ion).
Electrolyte requirements are higher in horses that participate in intensive exercise such as endurance races and horses that live in hot climates. The need is also higher in pregnant and lactating mares.
These horses experience a greater loss of electrolytes through sweat, urine, and milk supply. Electrolyte deficiency may result in reduced appetite, lower water intake, muscle weakness, lethargy, and other complications.
Targets for Digestive Health
- Support proper bodily functions
- Encourage hydration
- Promote gut motility
Efficacy
Fluid balance is greatly affected by digestive health. Electrolyte imbalances are observed in over 70% of horses with diarrhea due to depletion of water and electrolyte minerals.
This can have further negative consequences on the body, including disrupted muscle function and lethargy. [27]
Replenishing electrolytes lost due to an inflamed digestive tract or diarrhea can help horses regain their appetite and stimulate thirst.
The majority of research on electrolyte supplementation in horses focuses on performance or recovery from endurance training. However, electrolyte balance and proper hydration are important in all horses.
Supplementing with electrolytes can help horses replace the electrolytes lost through sweat and improve muscle glycogen synthesis after endurance training. [28][29]
These benefits may be attributed to increased water intake after electrolyte supplementation. [29]
A complete feeding program should incorporate electrolytes for both digestive and overall health.
THE VERDICT: Potential benefit linked to increased water intake and greater gut motility. More research is required to validate hypothesis.
9) Pectin-Lecithin Complex
Pectin is a type of fibre found in many fruits and vegetables. It is composed of polysaccharides, which are a long chain of sugar molecules.
Lecithin is a phospholipid derived from plants. Phospholipids contain fatty acids used for cell membranes, cell signalling, and many other physiological roles.
The combination of pectin and lecithin can be beneficial for digestive health in horses and can protect against gastric ulcers.
Together, they can protect the stomach lining from damage caused by acids without compromising the overall acidic environment of the stomach.
Targets for Digestive Health
- Protection against damage from stomach acids and bile
- Nutrient digestibility
- Microbial environment
Efficacy
Pectin acts as a prebiotic in the hindgut, supporting the growth of the beneficial microbial population.
Pectin is degraded by microbes to produce volatile fatty acids (energy) which can help maintain a healthy microbiome.
In the stomach, pectin creates a gel that binds to bile acids and protects the stomach lining from acidic degradation.
Lecithin forms a phospholipid layer in the squamous region of the stomach. This layer acts similarly to the protective mucous that is naturally present in the glandular region of the stomach. [30]
Two studies have shown that supplementing horses with a pectin-lecithin complex can aid ulcer healing. [31][32]
THE VERDICT: Suitable evidence of efficacy for digestive health.
10) Peppermint
Peppermint is a perennial flower that has been used throughout human history for its digestive benefits.
In traditional medicine, it is used to soothe digestive upsets, such as cramping, nausea, and diarrhea. Recently, it has been studied for irritable bowel syndrome (IBS) in humans.
Peppermint contains polyphenols and flavonoids known for their antioxidant effects. These active components may also promote the growth of beneficial bacteria for digestive health.
Flavonoids are also known for their anti-inflammatory, antibacterial and anti-viral effects.
Targets for Digestive Health
- Antioxidant & anti-inflammatory effects
- Reduces digestive irritations
- Beneficially alters the microbiome
- Nutrient digestibility
Efficacy
Peppermint is well-tolerated and has a palatable flavour. [33] It is often added to gut health supplements for horses to support gut comfort.
In broiler chickens, peppermint supplementation (1% in feed) resulted in increased muscle thickness in the digestive tract and improved intestinal morphology. [34]
These results suggest that peppermint may support intestinal structure and function. This could positively affect nutrient absorption and limit the infiltration of harmful bacterial products into the blood.
In a different study, broilers supplemented with peppermint oil (200 or 400 mg/kg diet) exhibited greater protein digestibility. [35]
In humans, peppermint is well-researched for IBS and appears to have antimicrobial and antioxidant effects. [36]
There is limited research available on peppermint’s use in horses. One study in horses supplemented with plant extracts that included peppermint demonstrated antimicrobial properties. [37]
Although there is substantial evidence supporting the digestive benefits of peppermint in other species, there is limited research on horses. While it is likely that peppermint exerts similar effects in horses, more studies will need to confirm this.
THE VERDICT: Evidence for digestive health in other species. Further studies are required in horses.
11) Glutamine
Glutamine is an amino acid that serves as a major energy source for cells lining the gastrointestinal tract.
Low levels of glutamine in the diet can impair tissue repair processes and cause atrophy of intestinal tissue leading to poor absorption of nutrients.
Glutamine is commonly added to equine gut health supplements. However, it is often included at low levels that will not have a meaningful impact on digestive health.
Glutamine needs to be supplemented at a high dosage in order to support a beneficial effect.
Targets for Digestive Health
- Energy source for cells of the GI tract
- Maintain gut integrity to prevent leaky gut
Efficacy
Glutamine is a non-essential amino acid, meaning it can be synthesized from other compounds in the horse’s body and does not necessarily need to be provided in the diet. However, there are times in which additional supplementation can be beneficial.
In most mammal species, glutamine is the preferred energy source for intestinal cells. These cells are not able to make glutamine and rely on adequate absorption from the diet and circulating levels in blood to meet their needs. [38][39][40]
The horse’s gut can extract up to 33% of circulating glutamine to use as an energy source. This supports many important processes including building the mucosal barrier to protect cells of the digestive tract from the acidic environment of the gut. [38]
Stress and Immune Response
Cells of the immune system also rely heavily on glutamine as an energy source. Conditions that activate immune cells such as viral infections and stress, can decrease glutamine levels in the blood.
Exercise, stress, and infections have been shown to decrease circulating glutamine in horses. [41] In these situations, cells of the immune system will use up a lot of glutamine which can limit its availability for intestinal tissue.
This is part of the reason why horses in travel and competition are susceptible to digestive upsets including gastric ulcers and diarrhea.
In one study, tissue was taken from the colon of horses and experimentally injured by oxidative stress. Adding glutamine helped minimize the effects of oxidative stress and lower the permeability of the tissue.
By lowering permeability, glutamine decreases the ability for infectious particles to enter the body and trigger an immune response. [42]
Feeding Glutamine
Glutamine is the most abundant amino acid in the bloodstream and much of it is used by the gastrointestinal tract.
Equine dietary supplements that contain glutamine need to provide a significant amount of it in order to have any appreciable effect on gut health. Unfortunately, many products on the market only provide low levels of glutamine.
THE VERDICT: Some evidence of efficacy in horses.
12) Aloe Vera
Aloe vera juice and gel are commonly used in horses suspected to have gastric ulcers.
Aloe vera gel derived from the inner leaf of the plant is known for its ability to soothe skin irritations and help heal lesions.
It has traditionally been used to support gastric health and exert a soothing effect on the digestive tract.
Targets for Digestive Health
- Anti-oxidant and anti-inflammatory effects
- Barrier protection between the acid and stomach lining
- Stimulate mucous production
Efficacy
The available research showing benefits of aloe vera for digestive health has been conducted in humans or animal models.
In rats that had gastric ulcers experimentally induced through high-acid intake, adding aloe vera gel to the diet helped decrease inflammation and supported ulcer healing. [51]
This beneficial effect was also observed in rats that had gastric ulcers induced by non-steroidal anti-inflammatory drugs. However, in this case the standard treatment with Omeprazole was more effective than aloe vera for preventing lesions from forming. [52]
To our knowledge, only one study has been done in horses. Researchers in Australia examined the effects of aloe vera gel compared to Omeprazole treatment in horses with gastric lesions.
The horses were given either 17 mg / kg aloe vera gel (equivalent to 8.5 grams for a 500 kg horse) twice per day or the standard treatment of 4 mg / kg Omeprazole.
After 28 days, 56% of the horses given aloe vera gel showed improvement in their ulcer scores but only 17% had totally healed gastric ulcers. In comparisons, 85% of the omeprazole group had improved scores and 75% had healed ulcers. [53]
Therefore, aloe vera gel can support tissue repair in horses with ulcers. But it is not as effective as omeprazole and should not be considered a replacement for therapeutic intervention.
THE VERDICT: Some evidence of efficacy in horses.
13) Bentonite Clay and Diatomaceous Earth
Bentonite clay is a popular natural supplement given to horses as a toxin binder. It works by binding to heavy metals and toxins to decrease their absorption and eliminate them from the digestive tract.
Diatomaceous earth is commonly used as a natural dewormer to lower parasite load in the digestive tract.
Although these are popular, they should be used with caution. Bentonite clay can have unintended effects on the uptake of important dietary minerals by binding them and limiting their absorption.
Diatomaceous earth has not been shown to have a significant effect on parasite load.
Targets for Digestive Health
- Bind and remove toxins from the digestive tract
- Decrease parasite load
Efficacy
Bentonite clay has an overall positive charge which allows it to bind negatively charged particles.
In several species, bentonite clay has been shown to bind toxins produced by moldy feed.
Aflatoxin is a common mycotoxin found in moldy grains. It can impair liver function and affect the overall health of your horse.
In pigs, adding bentonite clay to an aflatoxin-contaminated diet helped partially restore liver function. However, adding bentonite clay at a level of just 1% of the total diet also decreased magnesium and sodium absorption. [43]
More research is needed on horses. The undesirable effect on mineral availability suggests oral bentonite clay should be reserved for situations of known mycotoxin contamination of feeds and should not be used on an ongoing basis.
Long-term use of bentonite clay might cause secondary mineral deficiencies in the horse.
Diatomaceous Earth
Diatomaceous earth is derived from the fossils of microscopic marine organisms including diatoms, phytoplanktons and algae. It is high in silica which is abrasive and thought to injure parasites in the digestive tract.
Although it is marketed as a natural, chemical-free alternative to common dewormers, its effectiveness is not supported by research. To our knowledge, diatomaceous earth has not been studied in horses.
Since antithelmintic drugs are prohibited in organic farming, several studies have looked at diatomaceous earth as a potential natural alternative for livestock.
Unfortunately, studies have shown no benefit to including this in diets for cattle or sheep. There were no differences in fecal egg count when diatomaceous earth was added and no benefits to growth or other health measures. [44][45][46]
It should be noted that the composition of bentonite clay and diatomaceous earth can vary greatly depending on their source location. Batches of these products can differ from each other and might not be tested sufficiently to know their precise composition.
Although there is some evidence that bentonite clay can bind toxins, it can also impair the absorption of minerals and should be used with caution. The claims that diatomaceous earth can be used as a natural dewormer are not supported by research, although research has not been done on horses.
The Verdict Bentonite clay has potential toxin-binding properties but interferes with mineral absorption. No evidence of efficacy for diatomaceous earth.
14) Activated Charcoal
Activated charcoal refers to a carbonaceous residue that is heated to created pores and typically ground into a fine, black powder.
When ingested as a dietary supplement, these pores help absorb chemicals such as poisonous toxins and prevent their absorption in the gut.
Activated charcoal is commonly used to bind ingested toxins, particularly when a horse might have consumed poisonous plants. It is also thought to be useful for cases of colic and flatulence, although this has not been demonstrated in research studies.
Targets for Digestive Health
- Bind and remove toxins from the digestive tract
- Reduce microbial gas production
- May help horses with colic
Efficacy
Activated charcoal is a porous compound that can bind other compounds and is thought to have detoxifying benefits.
However, this effect is non-specific. Activated charcoal will not only bind toxins but also to other compounds that are beneficial to the horse.
There is limited research on activated charcoal in horses. One study investigated whether activated charcoal affects gut microbes and the compounds they produce.
Fecal samples were taken and the microbes were given typical feedstuffs along with five different levels of charcoal.
At levels reflective of typical feeding guidelines (30 grams activated charcoal for a 500 kg horse), activated charcoal had no effect on microbial gas production, VFA production or pH level.
This suggests that activated charcoal has no significant effect on microbes in the horse’s hindgut. [47]
Absorption of Toxins
This research did not look at potential effects in the small intestine of horses where ingested toxins would be absorbed. Therefore, more research is required to understand whether activated charcoal has beneficial detoxifying effects in horses.
Research in humans suggests the toxin binding benefit of activated charcoal is limited to a small subset of cases where patients show up in hospital within 2 hours of a drug overdose. Beyond this time, the toxin would be too far along the digestive tract for activated charcoal to have any benefit. [48]
The toxin-binding effect of activated charcoal could be beneficial in horses if it is given immediately after ingestion of a poisonous plant. However, this is likely not the reality in most cases.
Its other purported benefits on colic and flatulence have not been adequately demonstrated by research in horses.
Activated charcoal might have some utility in limited circumstances of suspected ingestion of poisonous plants. More research is needed to support any other perceived benefits.
THE VERDICT: Insufficient evidence to rate efficacy.
15) Antacids
Antacids are used in many species, including humans, to reduce acidity in the gastrointestinal tract.
Antacids commonly used in horses include:
- Aluminum hydroxide
- Magnesium hydroxide
- Calcium hydroxide
- Dicalcium phosphate
Antacids raise pH levels in the stomach by neutralizing gastric acids.
In horses, gastric ulcers are among the most common ailments associated with impaired digestive health. Ulcers form when acids erode the lining of the stomach.
Raising the pH of the stomach could temporarily reduce the risk of gastric ulceration, but may have a negative overall impact on your horse’s digestive health.
The stomach is acidic for a reason: to activate digestive enzymes, break down food and prevent the spread of pathogenic bacteria.
Targets for Digestive Health
- Neutralize gastric pH
- Reduce acidity to allow ulcers to heal
Efficacy
Early studies using an antacid of aluminum hydroxide (8.1 g) and magnesium hydroxide (4.8 g) showed that antacids could raise gastric pH levels in horses.
In 1992, horses were fed this antacid supplement and monitored for six hours post-administration. The gastric pH of these horses increased to greater than 4, but dropped back down before the four-hour mark. [49]
In 1996, a similar antacid supplement containing 30 grams of aluminum hydroxide and 15 grams of magnesium hydroxide was tested in adult horses.
Five horses were fed this antacid and monitored. [50] Gastric pH levels increased to 5 for two hours post-administration.
Multiple studies since then have confirmed that antacids can raise gastric pH levels for a short period of time. This led to widespread use of antacids in horses at risk of ulcers.
Risks of Antacids
However, researchers and equine nutritionists are concerned with the negative effects of antacid use.
The stomach is acidic for a reason. Raising pH levels above 4 may prevent proper functions of the stomach and interfere with the breakdown of food. This could impede normal nutrient absorption.
Additionally, there are concerns with using aluminum-based antacids. High levels of aluminum could negatively impact the digestibility of essential nutrients such as calcium, zinc, and phosphorus.
There is no long-term benefit to providing your horse with antacids. Antacids may provide short-term relief of gastric ulcer irritation but could cause more harm than good.
THE VERDICT: Poor to no long-term benefit for using antacids for digestive health.
Additional Equine Digestive Health Supplements
We have covered many popular equine digestive health supplements in detail above. However, this is not a complete list.
Below are some additional supplements that could benefit your horse’s digestive health based on demonstrated effects in humans or other species.
- Beta-glucan (a prebiotic)
- Omega 3 Fatty Acids
- Slippery Elm Bark
- Marshmallow Root Extract
- Corn Oil
- Sea Buckthorn Berry Extract
- Licorice
Factors to Consider when Choosing a Digestive Health Supplement
Digestive health supplements can be a great addition to your horse’s diet. How do you select which one is right for your horse?
Here are some important factors to consider when choosing the best supplement to add to your horses’s feeding program:
- Life stage of your horse: The digestive system will change throughout your horses lifespan. Young, growing animals and senior horses are more susceptible to digestive upset.
- Workload and training: Horses in heavy work are more likely to experience digestive issues such as gastric ulcers and hindgut acidosis. Competition horses should take preventative measures to reduce the risk of ulcers and dysbiosis.
- Digestive health status: If your horse has digestive health issues, such as gastric ulcers or colic, they are at high risk of experiencing recurring issues unless changes are made to their diet and management.
- Stress: Environmental conditions that induce stress can have a significant impact on the digestive tract and microbiome. Horses should be adequately acclimated to stressful situations such as trailoring to minimize the effects of stress on digestive function.
- Current feeding program: Your horse’s diet is a major contributor to digestive health. A forage-first diet that enables normal foraging behavours is your best defense against most digestive ailments.
- Foregut versus Hindgut: Some digestive ailments can be attributed to problems in the foregut (stomach) while other affect the hindgut. Determining which area of your horse’s gut needs more support will help you decide on the right supplement.
Our equine nutritionists are available to answer any questions you may have about different gut health support supplements and your horses’ diet.
Submit your horse’s diet online for a complementary analysis and our nutritionists can give you personalized recommendations.
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