Chronic diarrhea in horses often involves multifactorial etiologies and microbiome disruption. An integrative approach combining conventional care with TCVM, nutrition, probiotics, herbal medicine, and physical therapies can improve outcomes and support gut health.
Few conditions frustrate horse owners and veterinarians quite like chronic diarrhea. The horse looks miserable, the tail and hindquarters are perpetually soiled, and despite our best efforts, the problem persists week after week. If you’ve been there, you know the feeling.
The equine digestive tract, with its complex microbiome and sensitive physiology, is particularly vulnerable to disruption from environmental stressors, dietary changes, medications, and infectious agents. Unlike acute diarrhea, which often presents with clear infectious etiologies, chronic diarrhea in horses — defined as persistent loose or watery feces for seven to 14 days or more — frequently defies straightforward diagnosis and conventional treatment approaches (Harman, 2018; Sjolin et al, 2025). In fact, we achieve a definitive diagnosis in only 60% to 70% of cases, and often only through post-mortem examination. That’s a humbling statistic for any clinician.
The good news? An integrative approach — combining conventional veterinary medicine with complementary therapies, including Traditional Chinese Veterinary Medicine (TCVM), nutritional management, probiotics, and herbal medicine — offers the most comprehensive and effective strategy for managing this complex condition. Let’s explore how these modalities work together to give affected horses their best chance of recovery.
Understanding chronic diarrhea in horses
Chronic diarrhea in horses manifests along a spectrum of severity, from intermittent passage of soft feces to persistent watery diarrhea accompanied by free fecal water that contaminates the tail and hindquarters. The condition invariably involves disease of the large intestine, particularly the cecum and colon, which may result from either physical damage to the colonic wall or physiological disturbances of colonic function (Oliver-Espinosa, 2018). Understanding the underlying mechanisms is crucial for effective treatment (Harman, 2018).
Common etiologies
The causes of chronic diarrhea are multifactorial and often interrelated.
- Larval cyathostomiasis, caused by encysted small strongyle larvae, represents one of the most commonly diagnosed conditions, accounting for a significant proportion of chronic diarrhea cases in retrospective studies (Proudman et al, 2015).
- Idiopathic chronic colitis and inflammatory bowel disease, including granulomatous enteritis, lymphocytic-lasmacytic enterocolitis, and eosinophilic enterocolitis, constitute another major category (Schumacher et al, 2000).
- Alimentary lymphosarcoma, the most common intestinal neoplasia in horses, can cause significant cellular infiltration and chronic diarrhea across a broad age range (Oliver-Espinosa, 2018).
- Sand accumulation in the large intestine, particularly common in horses kept on sandy pastures or fed in sandy environments, can produce chronic diarrhea alongside weight loss and colic signs.
- Dietary factors, including feed changes, grain overload, and food intolerances — particularly to alfalfa — can trigger or perpetuate loose stool (Harman, 2018).
- Medications, especially non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics, are well-documented causes of colonic inflammation and microbiome dysbiosis that can lead to persistent diarrhea (Gustafsson, 2004).
The role of the equine microbiome
If there’s one concept that has revolutionized our understanding of equine GI health, it’s the microbiome. The equine intestinal microbiome — the collective genetic material of the microbiota inhabiting the gastrointestinal tract — plays a fundamental role in digestive health and disease. Research has revealed that microbial populations vary considerably between individual horses, even among those maintained on similar feeding programs (Costa & Weese, 2012; Al Jassim & Andrews, 2009). Furthermore, significant variation exists throughout different regions of the digestive tract within each horse (Ericsson et al, 2016).
The normal pH gradient of the equine intestinal tract — acidic in the stomach and upper small intestine, transitioning to alkaline in the large intestine — is maintained in part through microbial balance. These microorganisms reproduce rapidly, making their populations highly susceptible to changes in diet, environment, and medication exposure (Harman, 2018). When microbial populations migrate to inappropriate locations within the gut or when the balance is disrupted (a condition termed dysbiosis), intestinal inflammation and diarrhea can result.
Horses with diarrhea have been shown to possess lower bacterial diversity in their gut microbiota compared to horses with normal feces, though whether this dysbiosis is cause or consequence remains an active area of investigation (Weese & Munroe, 2011). Either way, it represents a key therapeutic target that integrative approaches are uniquely positioned to address.
The microbiome is also affected by environmental toxins. Glyphosate, the herbicide used in genetically modified organism (GMO) feeds, has been demonstrated to increase ulceration of the intestinal tract in pigs, suggesting potential similar effects in horses that may contribute to diarrhea through intestinal inflammation (Carman et al, 2013). This is an important consideration when evaluating feed sources for affected horses.
Traditional Chinese Veterinary Medicine perspective
TCVM offers a valuable framework for understanding and treating chronic diarrhea in horses. Herbal medicine has been employed for the treatment of gastrointestinal disease in horses for hundreds of years, and in modern
Chinese equine practice, the most common approach to chronic diarrhea involves herbal medicine alone or in combination with acupuncture (Xie et al, 1997). Understanding the TCVM perspective on digestion provides insight into treatment selection, even when Western therapeutic modalities are ultimately chosen.
TCVM organ systems and diarrhea
In TCVM theory, the Stomach receives and ripens incoming food and drink, with the pure essence descending to the Spleen while turbid components pass to the small intestine. The Stomach energy must move downward to accomplish this function properly. The Spleen is responsible for generating and containing the Blood and maintaining fluids in their proper locations. Spleen Qi deficiency can allow excessive fluid escape through the digestive tract, manifesting as diarrhea (Xie et al, 2022).
The Kidney Yang provides metabolic fire for digestion and assists the Spleen Yang in vaporizing fluids. When Kidney Yang is deficient, fluids are not properly transformed and instead escape downward as diarrhea. The Liver governs the smooth movement of Qi through vessels and organs and maintains an upward Qi flow while releasing bile to aid digestion.
Perhaps most relevant to modern horse-keeping: when Liver Qi stagnates — a common occurrence in horses experiencing the chronic stress of confinement, competition schedules, or frequent travel — it over-controls the Spleen and damages it, potentially leading to both ulcers and loose stool (Harman, 2018). The Large Intestine reclaims and excretes the more solid components of food and fluids while reabsorbing water from waste material.
Nutritional and dietary management
Dietary management represents a cornerstone of chronic diarrhea treatment and may be of paramount importance when definitive diagnosis proves elusive. Horses can be triggered by dietary changes even when consuming all-forage diets, with particular sensitivities to beets, alfalfa, and recent hay changes. Concentrated feeds containing numerous ingredients and wheat bran are significant potential triggers, as are grains (Mclaughlin, 2025).
Fecal water syndrome and chronic diarrhea are often caused by gastrointestinal transit time problems. Avoiding dewormers, antibiotics, steroids, and NSAIDs is crucial when possible, as these medications alter the natural bacterial balance in the colon (Mclaughlin, 2025). Feed changes should be made gradually, as rapid alterations in forage have been shown to significantly change microbiota composition (Respondek et al, 2008). Some horses show improvement when the roughage component is optimized, as the equine hindgut fermentation system requires approximately 36 to 48 hours to properly process roughage in the cecum (Xie et al, 1997).
Older horses, particularly those in their 20s and beyond, may develop poorly-formed stool due to an aging digestive tract, weakened microbiome, or poorly-functioning enzyme system. Horses fed wet diets due to dental issues may receive more water than they can process, resulting in diarrhea. In these cases, digestive enzyme supplementation may prove beneficial (Harman, 2018).
Probiotic and prebiotic therapy
Probiotic supplementation represents one of the most important interventions for horses with chronic diarrhea. Beneficial bacteria including Lactobacillus acidophilus, L. plantarum, L. casei, Enterococcus faecium, Bifidobacterium thermophilum and B. longum can help restore gut function. Any horse showing signs of ill health could benefit from at least two months of probiotic treatment (Harman, 2018). Specific products recommended by nutrition experts include Riva’s Remedies Pro Colon, Silver Lining Herbs, and Adored Beast Gut Soothe, administered for 60 to 90 days to help restore gut health (Mclaughlin, 2025).
Horses do not need to be on probiotics permanently but may require them to correct transit time issues. Quality is paramount, as many probiotics are poorly manufactured and unstable; by the time they are purchased and used, they may contain little to no active ingredients. Products with heavy preservatives, artificial flavorings, and sweeteners should be avoided (Harman, 2018).
Prebiotics, typically short-chain fructo-oligosaccharides, support the growth of probiotic bacteria and can be highly beneficial when included in formulations. Newer products incorporating soil organisms, microbial spores, or minerals that form the communication network for bacteria may offer superior support for the microbiome (Harman, 2018).
An innovative approach involves creating an organic garden corner on the property using grasses and herbs that horses naturally consume, allowing ten minutes of daily grazing to provide natural microbe populations that cannot be replicated in packaged products. This simple practice can make a meaningful difference in microbiome health.
Fecal microbiota transplantation
Fecal microbiota transplantation has been employed in equine practice for many years, with most research and clinical reports focusing on severe, acute cases or antibiotic-induced colitis (Mullen et al, 2016). The procedure involves administering intestinal contents from a healthy donor horse through a nasogastric tube to a recipient horse suffering from diarrhea. As microbiota DNA analysis becomes more widely available, it will be possible to accurately select optimal donor horses and potentially commercialize fecal microbiota preparations for easier administration (Harman, 2018).
Horses with a condition called intestinal dysbiosis, characterized by abnormal bacterial populations in the intestine, may particularly benefit from this therapy. Although pre- and probiotics are commonly used in these cases, treatment is not effective in many horses, making fecal transplantation a valuable alternative approach (Whitehead, cited in Veterinary Partner, 2018).
Natural remedies and supplements
Several natural remedies have demonstrated efficacy in managing chronic diarrhea.
- Raw garlic, known for its antimicrobial, antifungal, and antiviral properties, can be administered in small amounts daily (Mclaughlin, 2025).
- Psyllium husks serve a dual purpose: they can be gradually increased to a quarter cup daily to address transit time problems. If effective, this indicates a transit time issue. Psyllium is particularly beneficial for horses with sand accumulation, as it helps not only with sand removal but also with soothing and healing the gut wall (Sahagun et al, 2015). Psyllium-based products like Assure Plus provide comprehensive support for intestinal health beyond simple fiber supplementation (Harman, 2018).
- Plain aloe vera juice can be added to the feed bucket to soothe the digestive tract (Mclaughlin, 2025).
- Digestive enzyme products may prove especially useful for older horses whose overall body functions are failing or for those with long-standing absorption problems (Harman, 2018).
Herbal medicine approaches
Herbal medicine from various traditions offers effective treatment options for chronic diarrhea. Horses are well-suited to herbal therapy as they are capable of digesting raw plant material. Interestingly, many horses will selectively consume the herbs they need and reject those they don’t, providing a form of self-medication. The general dosing guideline is two to four times the human dose, whether using raw herbs or tinctures, though horses often respond to even lower doses due to their sensitivity to herbal energetics (Harman, 2018).
Western herbal formulations
Western herbal mixtures for diarrhea may contain yarrow, mullein, hops, marshmallow, meadowsweet, or cinnamon (when a warming herb is indicated). Formulations prepared with knowledge of herbal energetics are typically more effective than those using herbs purely symptomatically. High cannabinoid-containing hemp has demonstrated anti-inflammatory action in the gut, and early use in horses shows promise as herbal support for gastrointestinal health (Harman, 2018).
Chinese herbal medicine
Chinese herbal formulas are selected based on the TCVM diagnosis.
- For Spleen Qi Deficiency, formulas such as Shen Ling Bai Zhu San or Jing Tang’s Equine GI Formula may be appropriate.
- Kidney Yang Deficiency cases might require Si Shen Wan.
- For Damp-Cold in the Stomach, Wei Ling Tang may be utilized.
- In cases with infectious causes or Heat patterns, clearing formulas such as Yu Jin San would be selected.
Nineteen different herbal formulas specifically for treating various types of diarrhea in horses are documented in Chinese veterinary medicine, each targeting different underlying patterns (Xie et al, 1997). The selection of the appropriate formula requires accurate TCVM diagnosis based on tongue appearance, pulse quality, and clinical presentation.
Acupuncture and physical therapies
Acupuncture has been clinically demonstrated to be an effective adjunct in treating both acute and chronic diarrhea in horses and is now utilized at several universities with trained clinicians. For chronic cases, acupuncture may serve as a first-line treatment and may be all that is required for resolution. Effectiveness depends on accurate TCVM diagnosis with point selection based on this diagnosis.
Several universally useful points include Stomach 36, Bladder 20 and 21, Spleen 6 and 9, Large Intestine 10, and Governing Vessel 1 (Harman, 2018). These points can be used by practitioners without extensive TCVM training as a starting protocol for GI support.
Chiropractic care, while not often considered for diarrhea treatment, should be incorporated into the therapeutic plan for chronic cases. Horses not responding well to other treatments should be evaluated to ensure normal spinal motion throughout the vertebral column, particularly from the sixth thoracic vertebra caudally, where spinal nerve roots affect the digestive tract. Restricted motion in these areas can contribute to digestive dysfunction (Harman, 2018).
Homeopathic approaches
Homeopathy can be highly effective in treating diarrhea when the correct remedy is selected based on the totality of symptoms. Simple cases may respond to remedies such as Arsenicum album, Sulphur, Veratrum album, and Lycopodium. The Materia Medica offers numerous options, making detailed observation of the condition essential for remedy selection (Harman, 2018).
Homeopathic bacterial nosodes provide another therapeutic option. E. Coli and Salmonella nosodes, each administered in 200C potency for four days, may be particularly useful when these organisms are suspected but not definitively diagnosed. (Mclaughlin, 2025).
The advantage of homeopathic treatment lies in its safety profile and lack of adverse effects when properly prescribed.
Conventional medical interventions
While an integrative approach emphasizes natural therapies, conventional medications retain an important role in specific circumstances. Acute, severe cases are bestmanaged in hospital settings with access to intravenous fluid therapy, along with acupuncture, probiotics, and fecal transplants. Antibiotics should be used judiciously, as they are well-documented causes of severe colitis in horses through disruption of normal gastrointestinal flora.
In some cases, antibiotics are the inciting cause of severe diarrhea, and treatment must proceed without them (Gustafsson, 2004). The mainstays of supportive therapy include intravenous fluid administration, electrolyte supplementation where necessary, anti-inflammatory agents, and nutritional support.
Clinical outcomes and prognosis
The prognosis for horses with chronic diarrhea varies considerably depending on the underlying cause. Retrospective analysis of 51 adult horses with chronic diarrhea revealed that among the 35% that survived, most had larval cyathostomiasis (which responds well to appropriate anthelmintic therapy), colonic impaction, or undiagnosed conditions. Poor prognostic indicators include neoplasia, particularly alimentary lymphosarcoma, and severe inflammatory bowel disease (Proudman et al, 2015).
Horses recovering from chronic diarrhea may continue to show immunologic abnormalities even after clinical recovery. Studies have demonstrated that while lymphocyte responsiveness improves simultaneously with the recovery process, the responsiveness of lymphocytes in recovered horses remains markedly lower than in normal horses. Serum immunoglobulin A concentration is typically 50% lower in horses with chronic diarrhea compared to normal horses, while immunoglobulin G levels are often elevated (Targowski, 1978). These findings underscore the importance of long-term support for the immune system and microbiome in recovering horses.
Conclusion
Chronic diarrhea in horses represents a complex clinical challenge that demands a multifaceted therapeutic approach. While conventional veterinary medicine provides essential diagnostic tools and treatments for specific etiologies, the integration of complementary therapies — including nutritional optimization, probiotic support, herbal medicine, acupuncture, and physical therapies — offers the most comprehensive and effective strategy for managing this condition. The equine digestive tract’s sensitivity to medications, environmental stressors, and dietary factors makes natural approaches particularly well-suited to long-term management.
Understanding the central role of the microbiome in intestinal health and recognizing the TCVM perspective on digestive function provide valuable frameworks for treatment selection. Many horses require ongoing support given the often-unavoidable conditions that contribute to their diarrhea, and an integrative approach offers safe, effective therapies that can be maintained long-term without adverse effects.
As research continues to elucidate the complexities of the equine microbiome and expand our understanding of complementary therapies, the integrative approach to chronic diarrhea will continue to evolve and improve, offering hope for horses and their caregivers facing this challenging condition.
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AUTHOR PROFILE
Meghan Barrett, DVM, cVMA, CCRT, CVNN, CFVT, FFCP
