Horse Diarrhea: Causes, When It’s an Emergency & What to Do

Horse diarrhea is a symptom, not a diagnosis. Mild cases can happen with stress, transport, hospitalization, sudden feed changes, lush pasture, or rich hay. Merck notes that some healthy horses develop softer manure after stress or a diet change, but diarrhea can also be a sign of serious intestinal disease. In adult horses, acute diarrhea is often grouped under colitis or enterocolitis, which means inflammation of the large intestine or intestinal tract.

Important infectious causes include Salmonella, Clostridioides difficile or Clostridium perfringens, Potomac horse fever, and equine coronavirus. Merck also lists parasites such as cyathostominosis among possible causes of acute diarrhea in adult horses. In foals, infectious diarrhea has a different list of common causes, and rotavirus is one of the most common causes in breeding settings.

Noninfectious causes matter too. Antibiotic-associated diarrhea, grain overload, toxins, kidney or liver disease, inflammatory bowel disease, and protein-losing intestinal disorders can all lead to loose manure or true diarrhea. Some horses with chronic diarrhea also lose weight, develop low blood protein, or show ventral edema.

Because the same outward sign can come from a mild dietary upset or a life-threatening colitis, your vet usually looks at the whole picture: age, fever, appetite, manure character, recent antibiotics, travel, herd exposure, parasite control history, and whether there are signs of dehydration, endotoxemia, or laminitis risk.

See your vet immediately if your horse has watery diarrhea, repeated diarrhea, fever, colic signs, depression, weakness, reduced appetite, reduced drinking, blood in the manure, or signs of dehydration. Diarrhea can cause major fluid and electrolyte losses. Merck notes that horses with severe diarrhea can lose very large amounts of extracellular fluid each day, and dehydration may not look dramatic until it is already advanced.

Diarrhea is also more urgent if your horse recently received antibiotics, was transported, was hospitalized, had a sudden feed change, or if other horses on the property have fever or diarrhea. AAEP guidance advises isolating horses with acute diarrhea because contagious causes are possible, even before a diagnosis is confirmed.

A short episode of slightly soft manure in an otherwise bright adult horse with normal temperature, normal drinking, and no colic may be reasonable to monitor while you contact your vet for guidance. That said, if the manure becomes watery, the horse seems quieter than usual, or the problem lasts more than a day, the situation has moved out of the watch-and-wait category.

Foals are different. Any significant diarrhea in a foal deserves prompt veterinary attention, especially if the foal is weak, not nursing well, has a fever, or seems dehydrated. Foals can decline quickly.

Your vet will start with a physical exam and triage for dehydration, shock, endotoxemia, and colic. That usually includes temperature, heart rate, gum color, capillary refill time, gut sounds, hydration status, digital pulses, and sometimes a rectal exam or ultrasound depending on the horse’s condition. In severe cases, stabilizing circulation with fluids comes before chasing every test result.

Diagnostics often include bloodwork such as a CBC and chemistry panel to look for dehydration, inflammation, low protein, electrolyte changes, kidney involvement, and systemic illness. Fecal testing may include culture, PCR, toxin testing, or parasite evaluation. Merck notes that additional workups in horses with digestive disease can include fecal culture, parasite examination, virus testing, abdominal ultrasound, stomach tubing, and other targeted tests depending on the case.

Treatment depends on severity and suspected cause. Many horses need oral or IV fluids, anti-inflammatory medication, and close monitoring. If Potomac horse fever is suspected, your vet may discuss targeted antibiotic therapy. If clostridial disease, salmonellosis, or coronavirus is on the list, isolation and biosecurity become part of the plan. In horses with severe enterocolitis, your vet may also monitor for complications such as laminitis, low blood protein, and shock.

If the horse is unstable, referral to an equine hospital may be the safest option. Hospital care allows repeated bloodwork, large-volume IV fluids, around-the-clock monitoring, and faster response if the horse worsens.

Home care starts with calling your vet early, because diarrhea in horses can escalate fast. While waiting for instructions, keep your horse in a clean, quiet area with free access to fresh water unless your vet tells you otherwise. Remove grain, treats, and rich feeds for the moment, and do not give over-the-counter medications or leftover antibiotics unless your vet specifically recommends them.

Monitor and write down your horse’s temperature, appetite, water intake, manure frequency, manure character, and attitude. If you know how, note gum moisture and whether the horse seems tucked up, weak, or uncomfortable. Photos of the manure and a timeline of when signs started can help your vet.

Because infectious causes are possible, use practical biosecurity. Isolate the horse from shared water sources, avoid sharing buckets or tools, and wash hands and boots after handling manure. AAEP guidance for acute diarrhea supports isolation of affected horses while contagious causes are being considered.

Comfort matters too. Keep bedding dry, clean manure from the hindquarters and tail to reduce skin irritation, and watch carefully for new signs such as fever, colic, increased heart rate, or reluctance to move. If your horse becomes dull, stops drinking, develops watery diarrhea, or seems painful, that is no longer a home-monitoring situation.