Diarrhea: Is It Serious?
Horse and Rider|Fall 2020
Diarrhea: Is It Serious?
Learn how to tell the difference between loose manure and potentially deadly diarrhea—and how to protect your horse when the condition strikes.

What four words from a client make my heart race and my palms sweat? “My horse has diarrhea.” Not what you were expecting? You might think I’d be more concerned by such statements as, “My horse is down, and he can’t get up,” or, “He can’t bear any weight on his leg.” But in reality, it’s diarrhea that gets my full attention almost every time.

The reason is simple. If diarrhea is bad enough to make a client call the veterinarian, chances are, it either means there’s a really sick horse in a barn full of others at risk of getting sick, or it’s a chronic problem that will be almost impossible to diagnose and even more difficult to treat. Either way, there’s a good chance I’ll spend sleepless nights trying to figure out how to help.

Diarrhea is hard to diagnose and frustrating to treat. In a worst-case scenario, it can even be a life-threatening emergency that requires aggressive, immediate treatment. Even if it’s just a soggy mess, solving your horse’s diarrhea problem will require persistence and a heavy dose of patience.

Here, I’ll explain what diarrhea is and how it happens. Next, I’ll outline the factors that can help you determine whether the diarrhea is a serious health threat or simply an annoyance. Finally, I’ll give you the steps to take to protect your horse (and the other horses in your herd) when diarrhea strikes.

What It Is

Diarrhea is an intestinal disorder that causes frequent fluid manure evacuations. In other words, your horse poops a lot—and that poop is juicy, wet, and messy. Your afflicted horse might leave “cow pie” piles, might pass what appears to be a normal poop followed by a spray of water or, in the worst cases, might actually “spray the walls” with liquid.

But why does diarrhea happen? Normal equine digestion begins the moment your horse takes food in his mouth. He chews to break his meal into small, digestible pieces and mixes feed with saliva that helps to buffer stomach acids.

After swallowing, feed is passed to the stomach, where it’s exposed to acids, liquefied, and passed on to the small intestine where the first real absorption of nutrients begins. If the digestive tract is functioning properly, simple sugars, amino acids (components of protein), and some vitamins and minerals will all be absorbed during the one to three hours feed spends in the small intestine before it passes to the large intestine. The large intestine acts as a kind of fermentation vat, dependent on a healthy population of normal microorganisms (called the microbiota) that help break down large, fibrous feed materials.

Fermentation in the large intestine produces volatile fatty acids—an all-important source of energy for your horse—as well as vitamins and proteins. The large intestine also plays a critical role in storing and absorbing water from ingested feed. In fact, the large intestine is responsible for absorbing as much as 30 gallons of water every day. It’s a disruption of this function that leads to diarrhea.

If the large intestine isn’t functioning properly, its ability to absorb water will be compromised—meaning all of that excess liquid will be passed out in the manure. The large intestine can be compromised in a variety of ways. For example, excessive ingestion of carbohydrates changes the pH (a measure of acidity), which then upsets the microbiota balance. Ingesting sand can cause physical damage to the cells lining the intestine.


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Fall 2020