Diarrhea in Horses
Diarrhea means more frequent, looser-than-normal manure. It ranges from soft piles to profuse, watery stool. The biggest risks are dehydration, electrolyte loss, and—in adult horses—colitis (which can progress quickly). Some causes are contagious (for example, Salmonella, coronavirus), so isolation and biosecurity matter. A normal adult rectal temperature is 99–101 °F (37.2–38.3 °C); fever >101.5 °F (38.6 °C) increases concern. Foals dehydrate rapidly and need earlier veterinary involvement.
In the first hour
Confirm a rectal temperature, record full vitals, isolate, and start careful hydration support (fresh water available at all times). Log frequency, volume, and appearance of manure. Do not give over-the-counter anti-diarrheals or pain meds unless your veterinarian directs you. Withhold grain concentrates; offer plain, familiar hay. Call your veterinarian promptly if diarrhea is profuse/watery, foul-smelling, bloody, accompanied by fever or depression, or if the patient is a foal.
Diarrhea: First 12-Hour Owner Plan
Act calmly and focus on hydration, biosecurity, and good records while you contact your veterinarian. Adult fever >101.5 °F (38.6 °C) raises concern; ≥104.0 °F (≥40.0 °C) is an emergency. Any foal with diarrhea is urgent.
Confirm temperature and full vitals
Record rectal temperature, heart and respiratory rates, mucous membranes/capillary refill time, and simple hydration checks every 2–4 hours.
Isolate with strict biosecurity
House separately, no nose-to-nose contact, use dedicated buckets and tools, handle this horse last, and wash hands/boots after care.
Log stool and frequency
Time-stamp each episode and describe appearance (soft, cow-pat, watery, blood/mucus, odor). Note any worsening pattern.
Support hydration safely
Provide fresh water at all times; add a second clean bucket. Use electrolytes only if your veterinarian approves. Do not force oral fluids unless trained and directed.
Adjust feed sensibly
Withhold grain concentrates. Offer small, frequent portions of the horse’s usual hay. Avoid new feeds or supplements.
Call your veterinarian early
Same day for most adults; immediately for watery/bloody diarrhea, depression, colic pain, rapid dehydration, temperature ≥104.0 °F (≥40.0 °C), or any foal.
First-hour plan: owner-safe steps
01
Confirm temperature and vitals
Take a rectal temperature and record heart rate, respiratory rate, mucous membranes, capillary refill time, and hydration checks (gums, skin pinch).
02
Isolate and use biosecurity
House separately, no nose-to-nose contact, separate buckets and tools, handle this horse last, and wash hands/boots after care.
03
Log stool and fluids
Note each episode’s time and appearance (soft, cow-pat, watery, blood/mucus). Track water intake and urine output.
04
Hydration support (owner-safe)
Provide fresh water at all times. Offer an additional bucket with plain water; electrolytes only if your veterinarian approves. Never force oral fluids unless trained and directed.
05
Feed management
Withhold grain concentrates. Offer small, frequent portions of the horse’s usual hay. Avoid sudden feed changes and new supplements.
06
Call your veterinarian early
Same day for most adult cases; immediately if watery/bloody stool, fever ≥104.0 °F (≥40.0 °C), depression, colic pain, rapid dehydration, or any foal with diarrhea.
Red Flags for Horse Diarrhea: When to Call or Trailer Now
These signs mean urgent veterinary care. Follow your vet’s instructions before trailering—severe colitis can worsen with transport and some causes are contagious.
Watery or bloody diarrhea
Profuse watery stool or visible blood/mucus can lead to rapid dehydration and electrolyte loss. This is urgent.
Fever or signs of systemic illness
Adult fever >101.5 °F (38.6 °C) increases concern; ≥104.0 °F (≥40.0 °C) is an emergency—especially with depression or poor appetite.
Dehydration clues
Tacky/dry gums, prolonged capillary refill time (>2 seconds), sunken eyes, skin tent >2 seconds, or reduced urine output.
Colic pain or shock signs
Rolling, pawing, flank-watching, fast heart rate, cold extremities, weak pulse, or very pale/dark gums need immediate attention.
Foals and high-risk adults
Any foal with diarrhea is urgent. Also urgent: late-term broodmares, seniors, horses with known endocrine disease, or recent transport/stress.
Known barn cases or recent antibiotics
Recent antibiotic use, new arrivals, or confirmed contagious cases (e.g., Salmonella, coronavirus) require strict isolation and rapid vet guidance.
Likely Causes of Diarrhea in Horses by Context
Use these patterns to inform isolation and a clean history for your veterinarian. Only a vet can diagnose the cause.
Diet change or lush pasture
Sudden feed changes (grain, hay type) or rich spring/fall pasture can upset the hindgut and cause loose stool.
Infectious colitis (adult)
Bacterial or viral causes such as Salmonella or equine coronavirus can cause fever, depression, and diarrhea; isolation is essential.
Potomac Horse Fever (PHF)
Seasonal (late spring–fall) near rivers/canals/irrigated areas. Fever often precedes diarrhea; rapid dehydration is a risk.
Antibiotic-associated or right dorsal colitis
Recent NSAID or antibiotic exposure can injure the colon. Report all recent meds and doses to your veterinarian.
Sand/sediment enteropathy
Common in sandy regions or dry lots; chronic loose manure and weight loss can occur. Ask your vet about sand checks.
Foal-specific causes
Rotavirus, bacterial infections, parasites, or ‘foal heat’ diarrhea (usually mild, self-limiting). Foals dehydrate quickly—call early.
What to Tell Your Veterinarian
Precise, time-stamped details help your vet judge severity, contagion risk, and next steps. Avoid medications unless your vet directs you.
When diarrhea began, episodes per day, and description (soft, cow-pat, watery, blood/mucus, foul odor).
Rectal temperatures with times; heart and respiratory rates; mucous membranes and capillary refill time; dehydration checks.
Water consumed, appetite, urine frequency/amount, and any changes in salt/electrolyte intake.
Hay and grain types, pasture access, supplements/probiotics, and any sudden changes in the last 1–2 weeks.
Recent NSAIDs, antibiotics, dewormers (with dates), shows/transport, new arrivals, and known barn cases.
Where the horse is housed, isolation steps taken, and whether buckets/tools are separated and disinfected.
Horse Diarrhea FAQ: Fast Answers for Owners
When is diarrhea an emergency in horses?
Profuse watery stool, visible blood, depression, signs of dehydration, colic pain, adult temperature ≥104.0 °F (≥40.0 °C), or any foal with diarrhea requires urgent veterinary care.
Should I stop feeding my horse with diarrhea?
Do not feed grain concentrates. Offer small, frequent portions of the horse’s usual hay and fresh water. Avoid sudden diet changes unless your veterinarian directs you.
Can I give over-the-counter medications for diarrhea?
No. Do not give anti-diarrheals or pain medications unless your veterinarian instructs you. Some drugs can mask signs or worsen certain causes.
Is diarrhea contagious?
Some causes are (e.g., Salmonella, equine coronavirus). Isolate, use dedicated buckets/tools, wash hands/boots, and follow your veterinarian’s guidance on testing.
What about electrolytes?
Fresh water should always be available. Use electrolytes only if your veterinarian approves; inappropriate use can be harmful in some cases.
What should I track until the vet arrives?
Episode times and appearance, temperature and other vitals every 2–4 hours, water intake, urine output, appetite, and any new or worsening signs.
Useful links
Focus on hydration, PHF awareness, and accurate vitals. These links help you log signs and use tools safely while you coordinate with your veterinarian.