Diarrhea in Horses

Horse manure beside shovel.
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Diarrhea, or excessively loose stool, is a sign that something is wrong with your horse's health. Unless the problem clears up within about a day, you should call your veterinarian. A horse can very quickly become dehydrated when it has diarrhea, and dehydration can cause colic, a potentially life-threatening abdominal condition. The underlying cause of your horse's diarrhea may be a serious health problem that can be difficult for you to identify on your own.

Why Do Horses Get Diarrhea?

Diarrhea is a symptom, not an illness in and of itself, and often indicates that something is awry with a horse’s digestive system. Usually, a horse’s manure is a pile of solidly formed, rounded "buns" or "road apples." If the horse’s digestive system is altered in some manner, resulting in abnormal motility and altered fluid absorption, its manure can range from slightly runny to very loose and watery.

In severe cases, the loose manure may exit forcibly and end up covering stall walls and anything else standing in its path. Frequently, diarrhea may last for a day or two, resolve on its own, and you may never find the reason it occurred. But in some cases, it can be extremely acute and severe or become chronic and require ongoing treatment and vigilance.

There are many reasons horses get diarrhea. While most episodes are not a huge problem, diarrhea can also be an indication of a serious, life-threatening illness. Some of the causes of diarrhea in a horse include:

  • Behavioral, such as nervousness caused by being in a trailer or attending an event or the stress of moving to a new stable
  • Change of feed—either new feed the horse isn't used to or overfeeding its regular feed
  • Access to lush pasture
  • Food sensitivity or allergy
  • Spoiled feed
  • Antibiotics
  • Parasite load
  • Bacterial infection such as Salmonella
  • Equine gastric ulcer syndrome or EGUS
  • Excessive ingestion of sand
  • Potomac Horse Fever (PHF)
  • Nonsteroidal anti-inflammatory drugs (including Butazone)
  • Colitis
  • Poisoning such as slaframine poisoning
  • Cancer within the digestive tract
  • Rotavirus

If the diarrhea isn’t caused by something obvious that you know will pass (such as a minor behavioral cause), it’s time to discover what else could be causing it. Start to worry if, along with watery manure, your horse shows other symptoms, including:

  • Blood or mucus in the manure
  • Foul-smelling manure (beyond the normal manure smell)
  • Diarrhea that lasts more than 24 hours
  • “Projectile pooping” 
  • Other symptoms of colic
  • Elevated rectal temperature
  • Lethargy
  • Signs of weight loss or other health problems before the diarrhea started
  • Signs of dehydration (do a skin pinch or capillary refill test)
  • Pale gums
  • Lack of appetite

Treatment & Prevention

If your horse has diarrhea, you need to determine how severe it is. You may know that your horse gets nervous when the farrier comes, in the trailer, or at horse shows. In these cases, runny manure probably isn’t a sign of illness and once the stress is over, things will return to normal. Do make sure your horse is eating and drinking normally otherwise. If after 24 hours, the diarrhea is not gone, call the vet, who will help you find out what's causing the diarrhea and start your horse on the appropriate treatment.

The vet may take a fecal sample and/or blood sample to help determine the cause of the problem and suggest keeping the horse away from other horses, in case the cause is contagious. The vet may also give the horse medication to ease any abdominal discomfort and to help slow the gut down. Probiotics and other gut-balancing supplements may be given on the advice of your veterinarian. Depending on what caused ​the diarrhea, your horse might be given antibiotics or other medications. 

Avoiding diarrhea is very much like avoiding colic. It's hard to entirely prevent it, but smart preventive measures will help:

  • Avoid rapid changes to new feeds.
  • Introduce horses to lush pastures gradually.
  • Keep feeds, such as grains and concentrated food, locked down so horses that might get loose can’t help themselves.
  • Vaccinate your horse with the core vaccines and any others that are appropriate for your area.
If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.