Leaky Gut, Health, and Behavior: What’s the Connection?

Dr. Bill Vandergrift talks about leaky gut syndrome in horses during the 2021 EquiSummit, presented by Kemin Equine.

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Leaky Gut in Horses Leads to Behavior, Health Issues
A leaky gut is permeable, allowing pathogens to cross from inside the intestines into the rest of the horse’s body. | Courtesy Kemin

Has your horse undergone a subtle transformation, becoming girthy, resisting grooming, sporting a bit of a snarky attitude, and losing interest in her feed? These changes might not all be in your imagination or attributable to an inherently “sour” horse. Instead, they might result from a physical phenomenon called “leaky gut,” according to Bill Vandergrift, PhD, of International Equine Consulting Inc. Vandergrift presented “A Horse Owner’s Guide to Leaky Gut Syndrome” as part of virtual 2021 EquiSummit, presented by Kemin Equine.

The intestinal wall is delicate and extremely fine. In fact, only a single layer of cells, called enterocytes, separates the bacteria- and microbe-laden intestinal contents from the rest of the horse’s body. If that single-celled barrier falters, then the gut essentially springs a leak and becomes permeable. The result of intestinal contents seeping into the rest of the body is an unhealthy and unhappy horse, Vandergrift said.

“The enterocytes lie side-by-side and are glued together by proteins that form tight junctions,” Vandergrift explained. “In the face of inflammation, those tight junctions break down. Molecules from the intestinal contents can then slip past the enterocytes and are absorbed into the horse’s bloodstream.”

When the tight junctions break down, some of the enterocytes also break down. In extreme cases, ulcers might develop on the intestinal wall. “But you don’t have to have ulcers to have a leaky gut,” Vandergrift explained in his presentation.

Systemic inflammation and nutrient malabsorption are obvious consequences of leaky gut. But the immune system might also suffer. “There are sections of highly specialized enterocytes along the length of the intestine that play integral roles in the immune system,” Vandergrift explained. “In fact, the intestine contains 70% of the body’s immune system.”

In addition, Vandergrift pointed out that a leaky gut might contribute to a “leaky brain” as a result of systemic inflammation.

“There is a direct connection between the brain and gut,” he said. “The same mechanisms that break down the enterocyte tight junctions also compromise the blood-brain barrier, altering a horse’s behavior and neurotransmitter function.”

But what is the primary underlying cause of the inflammation that breaks down enterocytes and their tight junctions? Stress, he said.

Vandergrift pointed to the many ways and situations in which horses experience stress: physical stress during intense exercise and restricting feed around competition; emotional stress associated with showing, transport, and mixing with other horses; stress on the gastrointestinal tract due to decreased diversity of the intestinal microbiome; drug administration (anti-inflammatories, antibiotics); metabolic conditions; and others.

“Heat stress, experienced by competing on hot, humid days, is a big source of stress for horses and can induce leaky gut within hours,” he emphasized.

The good news is enterocytes replace themselves every two to three days, so repairing a leaky gut is certainly possible.

To stop the leak, Vandergrift presented approaches aimed at supporting the growth of healthy enterocytes held together by functional tight junctions.

Keys to success included:

  • Recognizing and managing stress;
  • Feeding pre-, pro-, and postbiotics as well as a high-soluble-fiber, low-starch diet to support a healthy, diverse intestinal microbiome;
  • Decreasing inflammation of the intestinal tract through the use of buffers and omega-3 fatty acids (fish oil); and
  • Providing key nutrients to support enterocyte growth, including zinc and antioxidants.

Take-Home Message

Leaky gut occurs when the tight junctions break down between the cells that divide intestinal contents from the rest of the body. This can lead to nutrient malabsorption, inflammation, a compromised immune system, and possible behavioral issues.


Written by:

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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