Dealing with a horse that has diarrhea requires careful attention to their feeding plan and to their daily management.
In some cases, diarrhea is a temporary annoyance that resolves itself with minimal intervention. Chronic cases in which diarrhea persists for at least 7 to 14 days can require greater intervention.
- Bacterial or parasitic infection
- Drug administration
- Diet and feed changes
In general, anything that disrupts the microbial population within the horse’s gut or irritates the intestinal lining can negatively affect gastrointestinal health and digestive function, potentially leading to diarrhea.
Diet is the first thing to be critically assessed when a horse is suffering from diarrhea.  Horses prone to gut issues can benefit from a feeding program that maintains a stable population of microbes in the gut.
In this article, we discuss the top ten tips for feeding horses that experience diarrhea, including avoiding abrupt changes to the diet and reducing excess starch consumption.
What Causes Diarrhea in Horses?
The reason that your horse has diarrhea may be difficult to identify. There are a number of potential causes, including bacterial or viral infection as well as non-infectious causes.
- Carbohydrate overload
- Moldy hay
- Stress from travel and competition
- Antibiotic use
- Use of pain medications, including NSAIDs
- Right Dorsal Colitis (hindgut ulcers)
- Inflammatory Bowel Disease
It is important to remember that diarrhea is a symptom and not a disease. Horses often develop diarrhea due to other underlying conditions.
Diet and Your Horse’s Gut Health
Horses have a very sensitive digestive system which is easily disrupted by changes in their feed or routine.
Horses are hindgut fermenters, which makes them unique from most mammals. The hindgut plays a critical role in extracting energy and nutrients from otherwise indigestible fibres found in forages. 
The cecum and colon which make up the hindgut are populated by a large community of microbes that ferment fibre in their diet. Normal gut function, digestion and immune health are highly dependent on the microbial population residing in the horseâ€™s gut.
A major by-product of microbial fermentation is volatile fatty acids (VFAs), which are short-chain fatty acids that are absorbed and used as energy by the horse.
These VFAs are also integral to support the turnover of cells of the intestinal lining. The VFAs support the growth of new cells in the gut, reduce inflammation and keep a proper pH balance. 
Any disturbance or shift in the population of bacteria within the gut can impact VFA production which can result in diarrhea. 
Feeding your horse in a way that supports proper hindgut fermentation and a balanced microbial population can help to reduce the risk of diarrhea in horses that are prone to gut issues.
Feed changes can also help to resolve diarrhea in your horse if they are currently dealing with this problem.
If you are looking for help with your horse’s diet, submit your current feeding plan online and our equine nutritionists can review it and give you suggestions to support digestive function in your horse.
Feeding a Horses with Diarrhea
Horses that regularly experience diarrhea are at greater risk of becoming dehydrated or developing secondary nutrient deficiencies.
Diarrhea often occurs with changes in gut motility and rapid transit of food through the digestive system. When feed and nutrients pass through the intestines too quickly, this reduces the amount of time for water and nutrients to be absorbed.
The result is loose, watery stools and reduced feed efficiency. Your horse is not absorbing as much water, nutrients and energy from the feed they consume, which can result in weight loss and other health problems.
Some additional complications of chronic equine diarrhea can include:
- Electrolyte imbalance
- Poor growth
- Lethargy or poor performance
- Mineral or vitamin deficiencies
- Poor skin, coat or hoof quality
- Protein loss (hypoproteinemia)
- Toxemia and Endotoxemia (absorption of toxins)
- Laminitis (in severe cases)
- Blood clotting abnormalities (rare)
As the cause of diarrhea is often unknown, it can be difficult to feed and manage horses that develop frequent bouts of diarrhea. If your horse has chronic diarrhea, their feeding program should be adjusted to minimize potential complications.
The first step is to have your veterinarian examine your horse to rule out infectious causes of diarrhea. If your horse is generally healthy but continues to experience diarrhea, feeding and management are your best options for resolving this symptom.
Below are some dietary recommendations to help minimize the onset of diarrhea and support the resolution of symptoms.
1) Ensure Adequate Nutrient Intake
Horses prone to diarrhea may be suffering from an undiagnosed gastrointestinal disorder, such as Inflammatory Bowel Disease.
Chronic diarrhea is often associated with malabsoption of nutrients and weight loss. Diarrhea-prone horses may require additional nutrients or caloric energy in order to meet core nutritional needs, support immune function and repair their intestinal lining.
Horses that experience long or frequent bouts of diarrhea may have reduced food intake or low appetite. An extended period of reduced food intake could result in nutrient deficiencies and impair the overall health and well-being of the horse. 
In particular, horses with impaired hindgut function might have lower absorption of B-vitamins that are produced in the hindgut. The addition of a balanced vitamin and mineral supplement may benefit these horses.
If your horse is losing weight because of chronic diarrhea, you may need to increase the energy density of your feeding program without adding starches which can exacerbate gut problems. This is best accomplished by adding essential fatty acids in the form of supplemental oils.
Different horses have different needs. For these reasons, it is recommended that you work with a nutritionist to develop a balanaced feeding plan optimized to meet the nutrient requirements of your horse.
2) Provide Plenty of Fresh Water
Horses that experience diarrhea lose excess water with their bowel movements and are at greater risk of experiencing dehydration. Sometimes, a horse that is dehydrated will consume less water to maintain electrolyte balance.
It’s important to ensure that your horse is drinking enough water to replenish what they are losing with their fecal matter, to support gut health and to reduce the risk of colic.
Make sure to feed your horse plenty of salt as well to encourage water consumption. Feed one to two tablespoons of plain loose salt per day and provide free choice, loose salt at all times.
If your horse has experienced a prolonged episode of diarrhea, supplementation with an electrolyte may be recommended to restore electrolyte levels.
Water should be provided at a lukewarm temperature (approximately 20Â°C or 68Â°F). Clean your horse’s water buckets every day and replace the water regularly to prevent bacterial growth.
3) Evaluate Forage Quality and Type
Choosing the right hay can also help prevent diarrhea and help conditions resolve more quickly. Hays with increased water-holding capacity may help to improve fecal consistency in horses with loose stools. Generally, grass hays such as Timothy hay are recommended over Alfalfa hay.
Short fibre hay cubes, pellets or chopped hay are generally recommended over long fibre hay for horses with gastrointestinal upset. 
Short fibre forage options can provide relief to an inflamed colon by reducing the workload of the colon. These forages are more digestible and easier for your horse to break down and absorb nutrients from.
Additionally, short-stemmed hay cubes and pellets provide a consistent, reliable, and well-balanced source of forage for horses during travel and competition. These may also be a good option for horses that are very sensitive and cannot handle changes in forage batches.
Hay should always be checked for mold prior to feeding. Moldy hay contains toxic by-products known as mycotoxins. Horses that ingest mycotoxins can develop diarrhea, along with numerous other symptoms.
4) Feed Fibre-Rich Foods
In addition to selecting the right hay for your horse, additives like beet pulp that are rich in fibre can help to slow gut transit times and increase fecal bulk.
Increasing the fibre and dry matter content of your horse’s diet will slow down the rate at which feed passes through your horse’s hindgut. Fibre that remains in the hindgut for longer may have a prebiotic effect, supporting the proliferation of beneficial bacterial colonies.
Beet pulp is also highly absorbent and can draw in more fluid from the gut, helping to restore normal gut motility.
- Beneficially alter the gut microbiome
- Increase the production of VFAs in the hindgut
- Promote mucosal repair
- Increase gut motility
- Increase fecal bulk through water absorption
- Promote anti-inflammatory benefits
A dose of 100 g daily for 3-6 months has previously been recommended. 
5) Avoid Sudden Dietary Changes
Horses have evolved to eat a fairly consistent diet with limited diversity. They rely on the microbiome found within the hindgut to break down their feed and synthesize certain nutrients.
Any changes in the diet need to be made slowly to allow the microbial populations to adapt. Research shows that significant changes in the microbiome can occur when new feeds are introduced. 
- Changing the type of grain or commercial feed
- Increasing the volume of grain
- Changing forage type
- Increasing fat intake
- Increasing access to pasture and grazing
It is generally recommended to allow for at least seven days of transition time to make a dietary change, but two weeks is preferable. If your horse is particularly sensitive, a longer transition time may be required. 
In addition to feeding a consistent diet, it is recommended to feed your horses on a consistent schedule. Unexpected changes in your horseâ€™s daily routine may cause stress.
Prolonged stress is known to negatively impact gastrointestinal function by reducing food intake and slowing down gut motility.
Abrupt changes in the horseâ€™s routine put them at increased risk of developing diarrhea. Horses that frequently travel for competition, move to a new boarding facility, or are admitted to a veterinary hospital may experience an abrupt dietary change and may develop diarrhea as a result.
Transitioning to Pasture
Additionally, a sudden increase in pasture access may result in gut problems. When horses transition to pasture, they often increase their consumption of sugars from the grass, known as fructans.
A sudden increase of fructans in the diet and over-consumption of these sugars can lead to diarrhea.   For this reason, it is recommended to gradually expose horses to pasture in the Springtime.
At the beginning of the season, restrict your horse’s pasture access to the early morning hours when sugar content of the grasses is lowest.
Over a period of several weeks, allow longer periods of time on pasture. While on pasture, always monitor your horse for signs of digestive upset, excessive caloric intake, and laminitis.
6) Reduce Starch Consumption
Over-consumption of starch from grain-rich feeds is a well-established risk factor for the development of diarrhea in horses.
This is common in performance horses that are often fed large quantities of commercial feeds to meet their high energy requirements. It can also occur in hard keepers that are fed sweet feeds or high grain diets because they otherwise have a hard time keeping on weight.
The horse’s small intestine is only capable of digesting a small amount of starch at a time. If too much starch is fed in a single meal, undigested starch will pass through from the small intestine to the horseâ€™s hindgut where it will be fermented.
The increase in lactic acid causes the pH of the hindgut to drop which produces an acidic environment. Increased acidity negatively affects the microbial population in the gut, killing off the â€śgoodâ€ť bacteria and allowing for the growth of “bad” bacteria.
Lactic acid also attracts water, drawing water into the intestinal lumen and increasing the risk of diarrhea.
- Decreased ability for the horse to ferment and utilize fibre
- Decreased absorption of VFAs for energy
- Disruption of the intestinal mucosal barrier
- Hindgut ulcers
- Changes in intestinal motility
- Intestinal inflammation
- Reduced capacity to absorb water and nutrients
The above changes to the horseâ€™s normal gastrointestinal health and function ultimately contribute to the development of diarrhea.
The general recommendation is that horses should receive no more than 2 grams of starch per kg body weight per meal. For a 500 kg (1100 lb) horse, this would be no more than 1 kg (2.2 lbs) of starch per meal.
7) Feed Many Small Meals
Horses evolved to spend 12 – 15 hours per day grazing and foraging. Feeding your horse many small meals throughout the day can prevent the development of stereotypic behaviours, reduce the risk of ulcers and generally support gut health.
A major risk factor for colic, hindgut acidosis, ulcers and other gut issues is feeding concentrates in one or two large meals per day.
Horses that require a large volume of commercial feed to support their high energy requirements should have their daily feed divided into numerous small meals spread evenly during the day. 
Dividing meals will reduce the amount of dietary starch that the small intestine has to process at a single time, making it less likely for the small intestine to reach its limit for digesting starch.
If your horse is experiencing diarrhea as a result of inflammation in their hindgut (such as right dorsal colitis), feeding small meals will limit how full the colon gets. This allows the colon to work at a reduced capacity which may help in the healing process. 
8) Feed Amino Acids
Glutamine and arginine are amino acids that are important for healthy digestive function. Amino acids are the building blocks of protein, necessary for maintaining a healthy intestinal tract.
- Decreasing inflammation
- Supporting the physical structure of the gastrointestinal tract
- Maintaining normal intestinal permeability
- Promoting intestinal healing
9) Feed a Probiotic and Yeast Supplement
Horses experiencing or recovering from diarrhea often benefit from probiotic supplementation to supply the gut with beneficial bacteria.
Providing exogenous sources of beneficial microbes can support fibre fermentation, immune function, VFA production, and help reduce intestinal inflammation.
The efficacy of probiotics supplements for horses with diarrhea depends on the underlying condition causing diarrhea as well as the strain of bacteria being fed and the number of Colony Forming Units (CFUs) provided. 
Of the various probiotics researched, Lactobacillus bacteria and yeast of the genus Saccharomyces appear to be the most successful for horses with diarrhea.
- Reduce the incidence of diarrhea
- Decrease the duration of diarrhea
- Prevent binding of unwanted bacteria to the intestine
- Reduce the concentration of toxins produced by unwanted bacteria
Probiotic supplements should provide a minimum of 5 billion CFUs per serving to support gut function. They need to be fed on an ongoing basis to have persistent beneficial effects.
Mad Barn has developed three different gut health supplements, each of which contains 20 billion CFUs of probiotics per serving.
For horses with chronic diarrhea, we recommend our Optimum Digestive Health pellets which contain probiotics, prebiotics, yeast, digestive enzymes, toxin binders and immune nucleotides to promote gut health and immune function.
10) Use Fats to Add Energy
Horses in intense training and competition have a high energy demand that is often met by high-starch feeds. However, these carbohydrate-rich feeds increase the risk of developing gastrointestinal issues, including diarrhea.
Fats are an alternative cool energy source that are digested and absorbed in the small intestine. Horses can adapt to diets that contain up to 8% fat, providing adequate caloric energy without compromising digestive function. By replacing starches in your horse’s diet with fats, you can promote gut health and hindgut function.
It is recommended to restrict oil intake during a bout of diarrhea. Once diarrhea has resolved, supplemental oils can be introduced gradually over 2-3 weeks, starting at 0.1 ml/kg bodyweight per day. 
There are a number of different fat sources that you can add to your horse’s diet, including canola oil, soybean oil, flax oil, camelina oil, corn oil or rice oil. We recommend consulting with a nutritionist to select the right fat for your horse.
Supplementing with oils high in anti-inflammatory omega-3 fatty acids helps ease inflammation along the digestive tract. 
If your horse suffers from frequent diarrhea, contact your veterinarian to determine the underlying cause. If infectious causes have been ruled out, it’s time to examine your horse’s feeding and management.
Managing diarrhea can be frustrating for horse owners and it can be a challenge to strike the right balance in your feeding program.
If you need assistance managing a horse that experiences frequent diarrhea, submit your horseâ€™s diet for a complimentary analysis. Our nutritionists will provide you with recommendations tailored specifically to your horse.
Is Your Horse's Diet Missing Anything?
Identify gaps in your horse's nutrition program to optimize their well-being.
- Valle, E. et al. Management of Chronic Diarrhea in an Adult Horse. J Equine Vet Sci. 2013.
- Oliver-Espinosa, O. Diagnostics and treatments in chronic diarrhea and weight loss in horses. Vet Clin Equine. 2018.
- Garber, A. et al. Factors influencing equine gut microbiota: Current knowledge. J Equine Vet Sci. 2020.
- Durham, A.E. 35 – Intestinal disease. Equine Appl Clin Nutr. 2013.
- Cohen, N. and Woods, A. Characteristics and risk factors for failure of horses with acute diarrhea to survive: 122 cases (1990-1996). J Am Vet Med Assoc. 1999.
- Frederick, J. et al. Infectious agents detected in the feces of diarrheic foals: a retrospective study of 233 cases (2003â€“2008). J Vet Intern Med. 2009.
- Ellis, A.D. and Hill, J. Nutritional physiology of the horse. Nottingham University Press. 2005.
- Magdesian, K.G. Nutrition for critical gastrointestinal illness: feeding horses with diarrhea or colic. Vet Clin North Am Equine Pract. 2003.
- Coenen, M. Macro and trace elements in equine nutrition. In Equine Applied and Clinical Nutrition. 2013.
- Geor, R.J. and Harris, P.A. How to minimize gastrointestinal disease associated with carbohydrate nutrition in horses. In: Proceedings of the Annual Convention of the AAEP. 2007.
- Longland, A.C. and Byrd, B.M. Pasture nonstructural carbohydrates and equine laminitis. J Nutr. 2006.
- Hoffman, R.M. et al. Hydrolyzable carbohydrates in pasture, hay, and horse feeds: direct assay and seasonal variation. J Anim Sci. 2001.
- Richards, N. et al. The effect of current grain feeding practices on hindgut starch fermentation and acidosis in the Australian racing Thoroughbred. Aus Vet J. 2006.
- Rowe, J.B. et al. Controlling Acidosis in the Equine Hindgut. Recent Adv Anim Nutr Aus. 1995.
- Clarke, L.L. et al. Feeding and digestive problems in horses: physiologic responses to a concentrated meal. Vet Clin North Am Equine. 1990.
- De Fombelle, A. et al. Feeding and microbial disorders in horses: 1-Effects of an abrupt incorporation of two levels of barley in a hay diet on microbial profile and activities. J Equine Vet Sci. 2001.
- Drogoul, C. et al. Feeding and microbial disorders in horses: 2: Effect of three hay: grain ratios on digesta passage rate and digestibility in ponies. J Equine Vet Sci. 2001.
- Hussein, H.S. et al. Effects of cereal grain supplementation on apparent digestibility of nutrients and concentrations of fermentation end-products in the feces and serum of horses consuming alfalfa cubes. J Anim Sci. 2004.
- Scott, E.A. et al. Inflammatory bowel disease in horses: 11 cases (1988-1998). J Am Vet Med Assoc. 1999.
- Mienaltowski, M.J. et al. Psyllium supplementation is associated with changes in the fecal microbiota of horses. BMC Res Notes. 2020.
- Tillotson, K. and Traub-Dargatz, J.L. Gastrointestinal protectants and cathartics. Vet Clin North Am Equine Pract. 2003.
- Mehmood, M.K. et al. Pharmacological basis for the medicinal use of psyllium husk (Ispaghula) in constipation and diarrhea. Dig Dis Sci. 2011.
- Johns, I. Managing acute colitis in the adult horse. UK Vet Equine. 2018.
- Wang, W.W. et al. Amino acids and gut function. Amino acids. 2009.
- Souba, W.W. et al. Glutamine metabolism by the intestinal tract. J Parenter Enteral Nutr. 1985.
- Beutheu, S. et al. Glutamine and arginine improve permeability and tight junction protein expression in methotrexate-treated Caco-2 cells. Clin Nutr. 2013.
- Wang, J. et al. Gene expression is altered in piglet small intestine by weaning and dietary glutamine supplementation. J Nutr. 2008.
- Mondello, S. et al. Glutamine treatment attenuates the development of ischaemia/reperfusion injury of the gut. Eur J Pharmacol. 2010.
- Schoster, A. et al. Probiotic Use in Horses â€“ What is the Evidence for Their Clinical Efficacy?. J Vet Intern Med. 2014.
- Yuyuma, T. et al. Evaluation of a host-specific lactobacillus probiotic in neonatal foals. Int J Appl Res Vet Med. 2004.
- Desrochers, A.M. et al. Efficacy of Saccharomyces boulardii for treatment of horses with acute enterocolitis. J Am Vet Med Assoc. 2005.
- Collado, M.C. et al. Probiotic Strains and Their Combination Inhibit In Vitro Adhesion of Pathogens to Pig Intestinal Mucosa. Curr Microbiol. 2007.
- Allaart, J.G. et al. Effect of Lactobacillus fermentum on Beta2 Toxin Production by Clostridium perfringens. Appl Envir Microbiol. 2011.
- Naylor, R.J. and Dunkel, B. The treatment of diarrhoea in the adult horse. Equine Vet Edu. 2010.
- Hess, T. and Ross-Jones, T. Omega-3 fatty acid supplementation in horses. R Bras Zootec. 2014.
- Garber, A. et al. Abrupt dietary changes between grass and hay alter faecal microbiota of ponies. PLOS One. August 18, 2020.