Causes of Diarrhea in Horses

When the horse’s digestive tract does not absorb a normal amount of moisture in the digesta, it can result in diarrhea.  These loose watery stools can be caused by a variety of conditions, some of which can be serious. Diarrhea can be an acute condition, meaning it will only last for a few days, or it can be a more chronic condition, which lasts much longer. Both acute and chronic diarrhea can be life threatening to a horse. Thus, if you are ever concerned with your horse’s health it is always advisable to speak with your veterinarian.

How to Know if Your Horse Has Diarrhea

There are scoring systems that evaluate and grade a horse’s manure based on moisture content. Many will differ on the score assigned, but all are meant to help owners judge if a horse’s manure is “normal” or is it too soft and runny in cases of diarrhea. They even rate manure as too dry and hard. Generally, the descriptions range from:

  • Watery diarrhea: The feces appear almost like urine, with mostly water/moisture expelled out of the rectum. It is recommended to speak with a veterinarian immediately.
  • Diarrhea: Feces are very loose with a high moisture content. Identify the cause.
  • Soft or loose feces: Appearance is like cattle feces and appear like “cow patties.” Monitor your horse.
  • Normal feces: Formation of fecal balls, with some moisture. Fecal balls can range from soft to firm.
  • Hard, dry feces: Less moisture content with high fiber content seen in the fecal balls. It is recommended to speak with veterinarian as dry and hard feces can lead to impaction colic.

Feces that are usually hard and dry are caused by a horse being dehydrated. However, the causes of diarrhea in horses are many.

Acute Causes of Diarrhea in Horses

Acute diarrhea is when the horse has loose and watery stools that lasts only a few days. While generally it is not considered dangerous for the horse, it can be. Especially in those cases of watery diarrhea where the horse is losing large amounts of fluid. This can be dangerous due to the loss in important nutrients like electrolytes.

Briefly, electrolytes are important for normal function in a horse. They help regulate the body’s pH balance, help with muscle contractions, nerve impulses, help keep a horse hydrated, among many other functions. Electrolytes are positive or negatively charged particles (ions) that include:

  • Magnesium
  • Sodium
  • Potassium
  • Calcium
  • Chloride
  • Phosphate

There are many causes of acute diarrhea. Some of these include:

  • New pasture growth: There is a high moisture content in lush, green pastures. The horse’s hindgut cannot absorb all the moisture and the excess is expelled as diarrhea. To learn more read Transitioning Your Horse to Spring Pasture.
  • Stress: Short-term stressors like transport or competition, among many others, can cause digestive upset and diarrhea.
  • Abrupt changes in the diet: It is always recommended to slowly transition a horse to its new diet to reduce the chance of digestive upset and diarrhea. To learn more, read Safely Transition Your Horse’s Diet.
  • Illness: There are a variety of viruses and other microorganisms that can cause short-term health challenges that cause diarrhea.
  • Potamic Horse Fever: An illness that can be treated successfully with antibiotics if caught early but leads to moderate to severe diarrhea. Can be fatal in up to 30% of horses infected if not treated. Other infectious diseases can also cause acute diarrhea.
  • Antibiotic use: Treatment of a horse with an antibiotic can disrupt the gut microbes leading to diarrhea.
  • Plant toxicities: Consumption of weeds or toxic plants can induce short bouts of diarrhea.
  • Foal Heat Diarrhea: Still not fully understood, but foals will experience diarrhea when their dam has her foal heat.

Chronic Causes of Diarrhea in Horses

Chronic diarrhea is almost always a concern for horse owners. While the transient, acute diarrhea can be caused by minor disruptions to gut function, chronic diarrhea is usually caused by more longer lasting and harmful conditions.

This is by no means an exhaustive list as there are many other causes of chronic diarrhea in horses, but some include:

  • NSAID (non-steroidal anti-inflammatory) toxicity or overuse: The NSAID pain relievers for horses if used for too long a period or given in too high a dose can lead to hind gut ulceration and chronic diarrhea.
  • Parasitic infection: Small strongyles encyst themselves in the intestine wall causing long-term damage and can lead to chronic diarrhea.
  • High NSC (non-structural carbohydrates) diets: Can lead to gastric ulcers and other longer term digestive disorders leading to chronic diarrhea. To learn more read Low NCS for the Performance Horse.
  • High fat diets: Too much fat in the diet can disrupt the gut microbe population and lead to chronic diarrhea.
  • Cancers: There are different types of cancers (i.e., lipoma) that can lead to chronic diarrhea.
  • Poor dental health: If a horse has difficulty chewing their feed, it is not digested properly and attracts more hindgut moisture leading to loose stools.
  • Sand accumulation: Over a long period, sand can accumulate in the hindgut. Acting like sandpaper it is abrasive against the digestive tract lining, leading to chronic diarrhea.

How Can We Manage Diarrhea in Horses?

The most important thing to manage diarrhea in your horse is to try and identify the cause. Then, if possible, eliminate that cause. As stated earlier, always speak with your veterinarian if you are concerned with your horse and diarrhea. In extreme cases, veterinarians are critical in giving supportive care like administering intravenous fluids.

From a nutritional perspective there are steps you can take to assist your horse that is experiencing diarrhea. These include:

  • Ensure horse is well hydrated: Always provide fresh, clean water. Can add flavoring or electrolytes to encourage drinking.
  • Maintain electrolytes: Depending on the situation, horse may need extra support. Can add electrolytes to the feed or provide a mineral/salt block.
  • Provide high quality and high fiber feeds: This will help hindgut health and function.
  • Provide pre- and probiotics: This will help maintain or establish a healthy gut microbe population. To learn more read How Prebiotics and Probiotics Help Your Horse.

Take Home Message

There are multiple causes of diarrhea in horses. These can result in acute and short-term bouts of diarrhea, which generally are not a concern. However, in any cases of severe diarrhea, it is always advisable to speak with your veterinarian as the horse will most likely need supportive care. Chronic cases of diarrhea are usually more concerning because they can be caused by a wide variety of debilitating health issues. However, once a cause is identified and if it can be eliminated, for many horses their feces will return to normal. If you have any concerns about your horse, the Tribute team is always available for consultation and please feel free to contact us.

Article By: Chris Mortensen, Ph.D.
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