Prebiotics are types of fibre that are given to horses as a food source for the beneficial microbes in the hindgut. Prebiotics support fibre digestibility, gut health, and nutrient assimilation in the hindgut.
Horses with disrupted digestive function, observed as bloating, discomfort, diarrhea, constipation, free fecal water, or intolerance to grain might benefit from prebiotics in the diet.
For horses that struggle with undesirable weight loss or hard keepers that need to gain weight, consider prebiotics to support the gut microbiome and increase nutrient absorption.
Prebiotics are soluble plant fibres that can not be digested by enzymes in the stomach or small intestine. This differs from probiotics which are living microorganisms.
Prebiotics reach the hindgut where they are broken down by specific microbes and function as substrates to stimulate the growth of probiotics. This helps the beneficial microbes proliferate and synthesize volatile fatty acids and vitamins that support a healthy gut and are beneficial to the horse.
The most common prebiotics are oligosaccharides which are long chains of sugar molecules that serve as an energy source for beneficial microbes. Fructo-oligosaccharides (FOS) are derived from chicory root. FOS primarily supports microbes such as Bifidobacteria.
Mannan-oligosaccharides (MOS) derived from yeast are added to equine diets as toxin binders. They work by binding to pathogenic microbes and toxins to limit their harmful effects. This helps support a healthy gut microbial environment and minimize inflammation of the intestinal wall.
Mad Barn’s Optimum Digestive Health (ODH) is a complete gut health supplement that contains Bio-Mos, a propriety prebiotic derived from yeast that has been shown to improve gut function in horses. ODH also supplies probiotics, digestive enzymes, and yeast to support hindgut health and feed efficiency.
Benefits of Prebiotics for Horses
A healthy gut is critical for supporting overall health and well-being of horses. The hindgut is home to trillions of micro-organisms that are necessary for digesting dietary fibre to meet the energy needs of the horse.
The hindgut is also the main site of synthesis for the water-soluble B-vitamins which have diverse roles in equine physiology.
Prebiotics nourish the beneficial microbes or probiotics, to help maintain a healthy gut environment and support efficient digestion and nutrient absorption.
Below are the top 6 science-backed benefits of prebiotics for horses:
1) Improved Tolerance to High-Grain Diets
High-grain diets are typically fed to performance horses to maximize energy supplied by the diet. However, rapid changes in the diet from high-forage to high-grain can negatively impact the hindgut environment.
Starch overload in the hindgut increases lactate production which lowers the pH, making the environment less favourable for beneficial microbes. This can contribute to hindgut acidosis, colic and laminitis in the horse.
Adding short-chain FOS to a high-barley diet in mature geldings minimized shifts in microbial populations in the hindgut, suggesting prebiotic supplementation can be beneficial in reducing hindgut disruptions related to starch overload. 
2) Improve Digestion in the Hindgut
Fibre digestion in the hindgut creates volatile fatty acids (VFAs) that are absorbed by the horse and used as an energy source. Shifts in the microbial populations can change the production of these and potentially leave horses in an energy deficit.
Horses given the prebiotic FOS for 10 days had increased levels of VFAs (acetate, butyrate, propionate) and lactate measured in feces. 
By providing prebiotics to nourish the microbes, they were able to produce more VFAs as an energy source for the horse. Horses with high energy demands, including growing and heavily exercised horses would likely benefit from prebiotics to increase VFA production by the hindgut.
3) Improve Insulin Sensitivity
Obesity and insulin resistance are common problems in horses that are over-fed and contributes to laminitis in these horses.
Obese horses (body condition score of 8 out of 9) supplemented with short-chain FOS for six weeks had improved insulin sensitivity. This occurred even with no change in body weight or body condition score by the end of the study. 
More research is needed to understand how prebiotics support insulin sensitivity in obese horses. Based on research in other animals, it could be related to improved gut barrier function and reduced inflammation that is commonly associated with insulin resistance.
Whatever the mechanism, improving insulin sensitivity is critical to support metabolic health in obese horses and to decrease the risk of laminitis.
Non-obese horses also benefited from prebiotic supplementation using Jerusalem artichoke meal which contains FOS. These horses had improved glucose removal from the blood after a meal, suggesting improved insulin sensitivity. 
In lean horses, improving insulin sensitivity can help prevent weight gain and support a healthy metabolism, particularly in the liver and muscle tissue.
4) Improve Digestibility in Senior Horses
Senior horses often experience weight loss or struggle to maintain their weight. Improving digestive function and nutrient assimilation might help support weight management in these horses.
On control diets without prebiotics, senior horses (>23 years of age) had lower dry matter, energy, and fibre digestibility than mature horses (average 7.5 years of age). However, when horses were given short-chain FOS for 25 days, these differences were no longer evident. 
This suggests that prebiotics can help senior horses maintain feed efficiency and extract more nutrients from their diet which might support weight gain in these horses.
5) Decreased Diarrhea in Foals
Foals are born without any antibodies and are susceptible to pathogens in the environment that can cause diarrhea and other infections. They must get antibodies from the mare’s antibody-rich milk called colostrum.
Mares fed Bio-MOS during the last two months of pregnancy and the first month of lactation produced colostrum with higher levels of antibodies. 
Foals consuming colostrum from mares fed Bio-Mos had higher levels of these antibodies in their blood and decreased incidence of diarrhea.
Although the study only looked at a small number of foals, out of six foals in the control group five got diarrhea that needed treatment. Of mares fed Bio-Mos, all five foals in the study did not get diarrhea. 
6) Protect against Sand Colic
Consuming sand and dirt can cause diarrhea, weight loss and colic in horses. In one study, clinically normal horses were given a supplement containing a mixture of prebiotics, probiotics and psyllium to evaluate whether this could prevent sand colic.
After just 4 days, higher levels of sand were measured in the feces and this continued until the end of the study at 31 days. The increased fecal sand output suggests this supplement can support gut health to protect against sand colic. 
However, in a study of horses that already had significant levels of sand in the colon, supplementation with a similar product did not affect sand accumulation in the hindgut. 
More research is needed to determine whether other factors in a gut health supplement could support sand clearance in horses and protect against sand colic.
Which Horses Could Benefit from Prebiotics
Supporting digestive health is crucial for the health and well-being of all horses. Up to 70% of the immune system is supported by the gut. Changes in the gut that irritate the intestinal lining or alter absorption patterns can trigger immune responses that affect the whole body.
One example is leaky gut syndrome, in which bacterial products such as lipopolysaccharide (LPS) enter the circulation. The ensuing inflammatory response can contribute to insulin resistance and laminitis.
Gut disturbances have been linked to several conditions and diseases in horses including: 
Age, diet, obesity and stress are the main factors associated with shifts in the microbial environment that may contribute to the onset of these illnesses.
The hindgut microbiome is relatively stable from 9 months of age to adulthood. Older horses (over 19 years of age) have lower diversity of microbes in the hindgut. 
Senior horses can benefit from prebiotic supplementation to support the beneficial microbes and improve nutrient digestibility and increase nutrient absorption. This is especially important for older horses that struggle to maintain a healthy weight or for those with Cushing’s/PPID that need to gain weight.
Performance horses undergoing heavy work and exposed to stressors during travel and competition are susceptible to hindgut disturbances.
Their diets might also consist of high levels of grain to meet their energy needs which can lead to starch overload and dysbiosis. These horses could benefit from prebiotics to help mitigate the negative effects of stress and diet changes on microbial populations and nutrient digestibility.
Supporting the hindgut in horses with metabolic issues such as insulin resistance and equine metabolic syndrome (EMS) is crucial for minimizing inflammation that is typically associated with these conditions and to decrease the risk of laminitis.
Horses with the following signs of metabolic dysfunction might benefit from prebiotics:
- High body condition score (obesity)
- Abnormal fat deposits on the tail head or neck (cresty neck)
- Frequent drinking and urination
- Recurrent laminitis
Characteristics of Equine Prebiotic Supplements
Any nutrient can be considered a prebiotic if it meets the following criteria: 
- Is resistant to digestion in the upper digestive tract and reaches the hindgut intact
- Is fermentable by hindgut microbiota
- Has beneficial effects on the horse’s health
- Stimulates growth of select microbes
- Is stable through feed processing
How do Prebiotics Work?
Prebiotics are naturally occurring in feed or can be added to improve the nutritional and health value of the diet. The most common type is dietary fibres that can not be digested in the upper gastrointestinal tract. Instead, they reach the hindgut intact and are digested by microbes.
Specific microbes break the chemical bonds between sugar molecules in the prebiotic and use those sugars for energy. This allows beneficial microbes such as Bifidobacteria to flourish and out-compete detrimental microbes such as E. coli.
Beneficial microbes support a healthy gut environment and overall well-being of the horse in several key ways: 
- Produce volatile fatty acids (VFAs): Short-chain fatty acids (primarily propionate, butyrate, and acetate) that the horse can absorb and use for energy. In total, the VFAs produced by the hindgut can supply up to 42% of the horse’s energy requirements. 
- Lower the gut pH: These VFAs also lower the pH of the gut which can limit the growth of pathogenic microbes.
- Produce antibiotics: The beneficial microbes produce antibiotic substances that can limit the growth of pathogenic microbes.
- Enhance natural defences of the gut: Microbial products such as butyrate can be used by intestinal cells to build the mucous barrier which protects cells of the intestinal wall from inflammatory products and the acidic environment of the gut.
- Modify immune cells of the gut: Beneficial microbes can communicate with immune cells nearby to help protect the horse from infection.
Common Prebiotics for Horses
FOS are found in many plants including wheat and barley. FOS are also found at high levels in chicory root and Jerusalem artichoke. For commercial purposes, FOS is typically extracted from chicory root or synthesized from sucrose by fungi such as Aspergillus niger.
FOS is a dietary fibre consisting of chains of glucose and fructose molecules. Sequences that are shorter than 10 molecules are considered short-chain FOS (scFOS).
Inulin is a common prebiotic derived from chicory root. It is a long-chain FOS containing up to 60 sugar molecules.
These prebiotics are typically added to equine diets to nourish beneficial bacteria, such as those of the genus Bifidobacteria or Lactobacilli.
By supporting the colonization of these bacteria, FOS increase the production of short-chain fatty acids and other acids that lower the pH in the intestinal environment. Lowering the pH helps inhibit the growth of pathogenic bacteria that can disrupt gut health. 
Mannan-oligosaccharides (MOS) is a toxin binder that is derived from the cell walls of yeast. These are not strictly prebiotic, because they are not consumed by microbes in the gut. Instead, they promote gut health by other mechanisms including binding to pathogenic microbes and supporting gut tissue.
MOS is commonly used in animal agriculture as an alternative to antibiotics because it can attach to lectins on the surface of pathogenic microbes such as E. coli, Campylobacter and Salmonella and reduce their colonization in the gut.
Although MOS do not directly feed beneficial microbes, decreasing the pathogenic load can support proliferation of beneficial microbes such as Lactobacilli.
MOS is positively charged and can bind bacterial components such as lipopolysaccharide (LPS) that are negatively charged. This prevents LPS from being absorbed and triggering inflammatory responses in the body. 
MOS supplementation in other animals has been shown to alter local immune cells in the intestine, helping them respond quickly to viral infections while dampening the immune response to allergens. This helps the animal respond appropriately to infections while minimizing chronic inflammation associated with a hypersensitive immune system. 
Bio-Mos is a propriety product developed by Alltech that is derived from the outer cell wall of a specific strain of yeast called Saccharomyces cerevisiae. It is used in a variety of livestock feeds to support gut integrity and animal performance.
This form of MOS can bind mycotoxins, which are molds found in feed that can negatively affect the horse’s health. Bio-Mos decreases their toxic effect and helps eliminate them from the gastrointestinal tract. 
In horses, Bio-Mos has been shown to support gastrointestinal integrity and stability, efficient transfer of nutrients from mare to foal, and performance. 
How to Feed Prebiotics to Horses
Prebiotics can be fed alone as a top dress. This can have benefits for digestive and metabolic health as reviewed in this article.
However, they are likely more effective when included in a complete gut health supplement that contains prebiotics, probiotics, and other factors that support the gastrointestinal tract.
Probiotics are live microbes and prebiotics are the foods they need to thrive. Combining the two can have additive effects compared to prebiotics alone. 
Mad Barn offers two gut health supplements that contain prebiotics (Bio-Mos), probiotics, yeast, digestive enzymes and other nutritive factors that support healthy gastrointestinal function.
Mad Barn’s Visceral+ has been clinically studied in horses with ulcers. It is formulated with natural ingredients including prebiotics and probiotics that support the body’s natural healing mechanisms and nourish the microbiome. It can be used during and following Gastrogard treatment or on its own in horses with ulcers or as a preventative measure.
Mad Barn’s Optimum Digestive Health is highly palatable pelleted formula designed to support hindgut health. It works in five key ways:
- Stabilizes the gut microbiome to reduce risk of dysbiosis and colic
- Contains digestive enzymes that improve nutrient digestibility
- Contains probiotics and other factors that support fibre fermentation
- Contains toxin binders like Bio-Mos that bind pathogenic microbes and toxins to neutralize them and help eliminate them from the body
- Is a source of natural immune modulators
Optimum Digestive Health is an all-in-one digestive health supplement that contains natural ingredients to optimize the gut microbiome and reduce the risk of digestive dysfunction and colic.
To learn more about these products or find out what is best for your horse, submit your horse’s diet for a complementary evaluation by our equine nutritionists.
Adverse Effects of Prebiotic Use
Prebiotics are a natural part of the equine diet and generally considered safe. Because microbes exist throughout the gastrointestinal tract, not just the hindgut, prebiotics might also influence microbial populations in the stomach and small intestine.
In one study, mature horses were given Jerusalem artichoke meal which is abundant in short- and long-chain FOS. The researchers observed changes in the abundance and diversity of microbes in the hindgut, as well as the stomach and small intestine. 
This suggests that digestion of prebiotics in this supplement begins in the foregut. This can increase VFA production in the stomach, decrease gastric pH and potentially damage the gastric mucosa. 
These studies highlight the need to choose prebiotics and probiotics that survive the acidic stomach environment without being digested there and reach the hindgut intact.
In several species, Bio-Mos and the probiotics found in Mad Barn supplements have been shown to survive the gastric environment and target the hindgut.  Therefore, these are unlikely to negatively shift bacterial species in the foregut.
Nonetheless, our complete gut health products also contain compounds that nourish and protect the gastric mucosa to support your horse’s foregut.
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