Diarrhea in Horses

Horse manure beside shovel.
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Diarrhea is a sign that something is wrong with your horse's health. Unless the problem clears up within a day, you should call your veterinarian. A horse can very quickly become dehydrated when it has diarrhea, and dehydration can cause laminitis, kidney failure, and in extreme cases, death. The underlying cause of your horse's diarrhea may be a serious health problem that can be difficult for you to identify.

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 nicely formed, rounded "buns" or "road apples." If the horse’s digestive system rushes its contents through too quickly, though, its manure can range from slightly sloppy 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. Diarrhea may last for a day or two, and you may never find the reason it occurred. But in some cases, it can 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:

  • Nervousness caused by being in a trailer or attending an event, which usually resolves as soon as the horse returns home
  • Change of feed—either new feed the horse isn't used to or overfeeding its regular feed
  • Change of stable
  • Food sensitivity or allergy
  • Spoiled feed
  • Antibiotics
  • Deworming medication
  • Parasite load
  • Salmonella
  • Equine gastric ulcer syndrome or EGUS
  • Sand enteropathy
  • Potomac horse fever
  • Nonsteroidal anti-inflammatory drugs (including Butazone)
  • Colitis
  • Poisoning such as slaframine poisoning
  • Cancer
  • Rotavirus

If the diarrhea isn’t caused by something obvious that you know will pass, 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
  • A change in the horse's TPR (temperature, pulse, respiration) values that suggests it has a fever
  • Lethargy and/or low energy
  • Signs of weight loss or other health problems before the diarrhea started
  • Signs of dehydration (do a skin pinch or capillary refill test)

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 will probably take a fecal sample to help determine the cause of the problem and suggest keeping the horse away from other horses, in case the problem turns out to be contagious. The vet may also give the horse medication to ease any discomfort and to help slow the gut down (e.g., Kaopectate or psyllium fiber). 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 drugs. 

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.
  • Deworm your horse regularly.
  • Vaccinate your horse with the core vaccines and any others that are appropriate for your area.

If you have a horse with diarrhea, clean the mess up as soon as possible. If there are disease-causing bacteria in the diarrhea, you don't want infections spreading to other horses (or other animals) that may be nearby. Using a hose and a bleach-based cleanser will help kill the germs.

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.