Why Does My Horse Have Diarrhea? Causes and Care

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

Why is my horse having diarrhea? Most of the time it comes down to a sudden diet change, stress, sand in the gut, parasites, or an infection that inflames the colon. A single soft pile in an otherwise bright, eating, drinking horse is often minor, but diarrhea that is watery, frequent, or paired with fever, colic, or depression needs a veterinarian quickly. This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

• A brief bout of semiformed manure after a feed change, a trailer ride, or a move is common and usually not medically important if the horse is otherwise healthy [1].
• Watery or explosive diarrhea, especially with fever, colic, or a dull attitude, is an emergency. Call your veterinarian now.
• Dehydration is the fastest danger. Check gum color, capillary refill, skin tent, and how much the horse is drinking and urinating.
• Do not reach for human antidiarrheal drugs or antibiotics. Some antibiotics actually cause diarrhea in horses [1].
• Chronic diarrhea lasting longer than a month is a different problem and needs a full workup, often including sand and parasite testing [2].

What the Sign Looks Like and What Is Normal

Normal horse manure is formed into soft balls that break apart when they hit the ground. It should be fairly consistent from day to day. When owners ask why their horse has diarrhea, they are usually describing one of three things: loose piles that still hold some shape, cow-patty consistency, or true watery diarrhea that runs down the tail and legs.

The difference matters. Semiformed feces can show up when a horse is first turned out on lush pasture, switched to alfalfa hay, or handled through a stressful event like a trailer ride, a race, a show, or a visit to a veterinary hospital. That kind of change is not of medical importance as long as the horse is healthy in every other way, and the manure usually returns to normal once the horse adapts to the new diet or the stress passes [1].

So is it normal for horses to have diarrhea? No. Truly watery diarrhea is never normal. Loose manure that firms up within a day or two in a horse that is eating, drinking, and acting fine is common and usually harmless [1]. Watery manure that persists, gets worse, or comes with other signs is a medical problem.

Why Is My Horse Having Diarrhea? The Main Causes

Diarrhea in adult horses can be acute or chronic. Acute cases often trace back to an infection, and the list of infectious agents includes Salmonella, Neorickettsia risticii, Clostridium difficile, Clostridium perfringens, Aeromonas species, coronavirus, and cyathostominosis (a heavy small strongyle burden) [2]. Chronic diarrhea, meaning it lasts longer than one month, is often harder to pin down and can involve inflammatory or neoplastic conditions of the intestine, sand enteropathy, inflammatory bowel disease, or intestinal lymphosarcoma [2].

Diet and management sit behind a large share of cases too. Grain overload, antimicrobial treatment, and a long list of toxic plants and chemicals can all trigger diarrhea or semiformed manure [1]. The equine hindgut runs on a rich bacterial population that supports digestion and overall health, and anything that disrupts that microbiome can loosen the manure [3].

Diet and Stress

This is the most common and least scary category. A horse moved to a richer diet or pushed through a stressful event may produce semiformed feces for a short time. The fix is usually patience and a gradual return to routine. If the horse stays bright, hydrated, and interested in food, there is rarely anything to treat [1].

Sand

Horses grazing on sandy ground can swallow sand that settles in the gut and irritates the intestinal lining. Sand enteropathy is one of the recognized causes of chronic diarrhea in adult horses [2]. Clues include recurring loose manure, a dull coat, weight loss despite good feeding, and sand grit in the manure or on a fecal sand test. This problem tends to build slowly, so it often shows up as the answer to "why does my horse always have diarrhea."

Parasites

Cyathostomins (small strongyles) and large strongyles can cause serious intestinal disease. One case report described a foal with acute profuse diarrhea that did not respond to treatment, and postmortem examination found strongyle infection along with verminous arteritis, colonic infarction, ulcerative colitis, and Salmonella [4]. That is an extreme example, but it shows how much damage parasites can do when they are not controlled. Cyathostominosis is listed among the infectious causes of acute diarrhea in adult horses [2].

Colitis and Infection

Colitis means inflammation of the colon, and it is the engine behind many severe diarrhea cases. Salmonellosis in horses can cause severe enteritis with diarrhea, fever, and colic, and it tends to hit foals, hospitalized horses, and immunocompromised animals hardest [5]. Carrier horses can shed Salmonella off and on, which means they can pass it to other animals and to people [5]. That zoonotic risk is one reason your veterinarian may ask about handling precautions.

Other Causes Worth Knowing

The list of less common triggers is long. It includes thromboembolic disease of the colon, peritonitis, kidney failure, hyperlipidosis, and a wide range of toxicoses such as blister beetle (cantharidin), salt poisoning, monensin, organophosphates, oleander, Japanese yew, castor bean, avocado, acorn or oak, and mycotoxicoses [1]. Liver disease can also present with diarrhea alongside weight loss, jaundice, edema, or photosensitization [6]. If your horse had access to anything unusual, say so when you call.

Red Flags That Make It an Emergency

Call your veterinarian immediately if you see any of these:

• Watery or explosive diarrhea, especially if it is frequent or projectile
• Fever, or a temperature you have not measured but the horse feels hot
• Colic signs such as pawing, rolling, looking at the flank, or lying down more than usual
• Depression, dullness, or a horse that will not eat
• Dry or tacky gums, a skin tent that stays up, or dark, scant urine
• Diarrhea after grain overload or exposure to a toxic plant or chemical
• Profuse diarrhea in a foal, which can decompensate fast

Horses with diarrhea are also likely to develop more profound hyperchloremia, an electrolyte imbalance that tracks with how sick the horse is and with kidney function [7]. That is a laboratory problem you cannot see from the barn, which is exactly why bloodwork matters in these cases.

Safe Things You Can Do at Home While You Wait

• Offer fresh, clean water at all times and consider a second bucket in a different spot to encourage drinking.
• Check hydration every few hours. Press on the gum above the teeth and count how long the color takes to come back, lift the skin on the neck and see if it snaps down, and note how much the horse is urinating.
• Take the horse's temperature with a rectal thermometer and write down the number.
• Remove grain, rich hay, and any new feed. Offer plain grass hay if the horse wants to eat.
• Keep the horse in a quiet, shaded area with easy access to water and a clean, dry place to stand.
• Collect a fresh manure sample in a clean bag or container for the veterinarian.
• Do not give human antidiarrheal medication, and do not give antibiotics unless your veterinarian prescribes them. Antimicrobial treatment itself is a recognized cause of diarrhea in horses [1].

If you are managing diarrhea in another species at the same time, our guides on dog diarrhea with blood and mucus and cat diarrhea causes and home care cover the same principles of hydration checks and red flags.

What Your Veterinarian Will Check and Test

Your veterinarian will start with a full physical examination. That means heart rate, respiratory rate, temperature, gum color, capillary refill time, skin tent, gut sounds, and a hands-on check for sand or gas. The exam is how they decide whether this is a mild diet-related change or something that needs aggressive care.

From there, expect some combination of:

• Bloodwork to check electrolytes, kidney values, and hydration status. Chloride and creatinine are both meaningful markers in horses with diarrhea [7].
• A fecal exam for parasite eggs, sand, and sometimes bacterial culture or PCR for Salmonella and other infectious agents [2][5].
• A rectal examination or ultrasound to look for sand, thickening, or other intestinal changes.
• Testing for specific infections such as Neorickettsia risticii or Clostridium species when the history fits [2].

Treatment depends entirely on what is found. Many horses need intravenous fluids to replace what they are losing. Some need specific antimicrobials, anti-inflammatory drugs, or parasite treatment. Your veterinarian will calculate any drug dose from your horse's weight and current health, so never borrow a dose from another horse or an old bottle.

Prevention and Monitoring

The best defense is a steady routine. Make feed changes slowly over one to two weeks. Keep pasture turnout consistent. Manage stress around travel and shows as much as you can. Follow a deworming plan your veterinarian designs for your region and your horse's risk, since parasite-related diarrhea is preventable in most cases [2][4].

Watch your horse's manure as part of your daily check. You already know what normal looks like for your horse, so you will notice a change early. If you live on sandy ground, ask your veterinarian about periodic sand screening, because sand enteropathy tends to be chronic and easy to miss [2].

Keep a simple log of manure consistency, water intake, and attitude. That record is genuinely useful when you call the clinic, and it helps your veterinarian decide how urgent the situation is.

Limitations and When to Contact a Veterinarian

This article cannot tell you what is causing your individual horse's diarrhea. Only a veterinarian who examines your horse and runs the right tests can do that, and every case needs that hands-on evaluation.

Call the same day for loose manure that has lasted more than a day or two, a horse that seems slightly off, or any diarrhea in a horse with a known sand or parasite problem. Go to emergency care now for watery or explosive diarrhea, fever, colic, depression, a horse that will not eat or drink, or diarrhea after grain overload or toxic exposure. Schedule a routine visit for chronic loose manure lasting longer than a month, gradual weight loss, or recurring bouts that never fully resolve [2].

Frequently Asked Questions

Can diarrhea in horses clear up on its own?

Yes, mild semiformed manure tied to a diet change or a stressful event often returns to normal once the horse adapts, with no treatment needed [1]. That only applies when the horse is healthy in every other way. Watery diarrhea, fever, or a dull attitude means you should call your veterinarian instead of waiting.

Why does my horse always have diarrhea?

Long-lasting or repeating diarrhea usually points to a chronic problem such as sand enteropathy, inflammatory bowel disease, intestinal lymphosarcoma, or a heavy parasite burden [2]. These conditions tend to develop slowly and are easy to dismiss as "just loose manure." A full workup is the only way to sort out which one you are dealing with.

Why does my horse have explosive diarrhea?

Explosive, watery diarrhea usually means significant inflammation in the colon, often from an infectious cause such as Salmonella, Clostridium, coronavirus, or cyathostominosis [2]. It can also follow grain overload or exposure to a toxic plant or chemical [1]. This pattern is an emergency because horses lose fluid and electrolytes fast.

Is it normal for horses to have diarrhea after a feed change?

Loose manure after a switch to lush pasture or alfalfa is common and typically not medically important if the horse is otherwise well [1]. The manure usually firms up as the horse adjusts. Make future changes gradually, and call your veterinarian if the looseness lasts more than a couple of days or the horse starts acting sick.

Can I give my horse human diarrhea medicine?

No. Do not give human antidiarrheal drugs or leftover antibiotics to a horse with diarrhea. Some medications, including certain antimicrobials, can actually cause diarrhea in horses [1]. Your veterinarian will decide what treatment is safe and will calculate the correct dose from your horse's weight and health.

Related Articles

• Chicken Diarrhea Causes
• Cat Diarrhea: Causes, Home Care, and When to Worry
• Kitten Diarrhea: Causes, Safe Home Care, and Emergency Signs
• Dog Diarrhea with Blood and Mucus: What It Means and What to Do
• Dog Diarrhea: Safe Home Care and When to Call the Vet
• Cat Diarrhea with Mucus: Causes and When to Worry

References

1. Miscellaneous Causes of Diarrhea in Horses - Digestive System. Merck Veterinary Manual.
2. Overview of Infectious Diarrheal Diseases in Horses - Digestive System. Merck Veterinary Manual.
3. A Comprehensive Review of the Equine Gut Microbiome in Health and Disease. Veterinary sciences, 2026.
4. Infection by Strongylus edentatus and Strongylus vulgaris in a warmblood crossbred foal in Ontario. The Canadian veterinary journal = La revue veterinaire canadienne, 2026.
5. Equine Salmonella in Argentina: Genetic relatedness with humans and other animal species and first detection of serovar Freetown. Comparative immunology, microbiology and infectious diseases, 2026.
6. Clinical Signs of Liver Disease in Horses. The Veterinary clinics of North America. Equine practice, 2026.
7. The magnitude of hyperchloremia in horses is associated with diarrhea and renal function. American journal of veterinary research, 2025.

Further Reading

• Merck Veterinary Manual: Horse Owners