Take a look at how exercise, diet and other stressors can affect the health of your horse’s gut permeability.

Leaky gut syndrome refers to a range of conditions in which the barrier function of the gastro-intestinal tract (GIT) has been compromised. This makes the intestinal wall permeable to harmful or toxic substances that should not freely enter the bloodstream of the horse. In addition to beneficial nutrients, the feedstuffs that your horse ingests may contain pathogens, toxins and poisonous plant or animal material. Therefore, one of the most important functions of the GIT is to act as a barrier between the external and internal environment.

There are several stressors that can damage the GIT barrier, and Leaky Gut Syndrome (LGS) is often the result of two or more of these stressors acting together. For example, a performance horse in training consumes high starch diets and experiences the stresses of exercise, training and handling. This, compounded with the stress of the stall environment, can negatively impact the GIT barrier leading to LGS. This article will introduce the horse owner to some of the main factors that cause leaky gut, with an emphasis on stress.

Understanding the role of stress

Stress itself is normal and benefits horses in many ways. However, excessive stress, even for short periods of time, can result in a loss of homeostasis and damage to the gut lining. Signs of damage include fatigue, reduced performance, lack of appetite, laminitis, loose manure and more. There may also be symptoms not typically associated with gut health, such as poor behavior or skin allergies that indicate injury to the GIT barrier.

The way in which excessive stress contributes to leaky gut is not fully understood. Stress impacts hundreds of different signaling molecules and hormones, such as cortisol and adrenaline. In turn, these molecules effect numerous tissues and organs including the GIT and brain. Some stressors lead to increased stomach acid secretion which can alter nutrient composition, the GIT microbiome (bacteria) and contribute to dysbiosis (sick microbiome). Ultimately, this stress results in low-grade inflammation that is often associated with increased intestinal permeability – leaky gut.

Part of the difficulty when dealing with stressors, whether internal or environmental, is that a horse’s intestinal immune system may not respond optimally to a leak of toxins or bacteria into the bloodstream. An unwanted disturbance of gut microbiota and/or leaky gut can also result in an inappropriate innate immune response, which can lead to allergies, behavior challenges and many systemic diseases.  That’s why it’s important to identify and attempt to limit the stressors in your horse’s environment.

Additionally, it is critical to recognize signs of leaky gut and to prevent or minimize this condition through quality nutrition and care.

Exercise, training and travel

Not all exercise contributes to Leaky Gut Syndrome. Most activity that is mild to moderate in intensity and duration is very beneficial to overall health, including health of the GIT. Leaky gut is more likely to occur when exercise is of high intensity, in hot/humid conditions or of long duration (endurance, competitive trail riding). In these instances, dehydration, metabolic stress and immune suppression may happen, which can then lead to a leaky gut. Fatigue, often associated with acute or chronic exercise, may signify a suppression of normal immune responses as well as being an indicator of a leaky gut.

When it comes to promoting gut health, the potentially negative effects of travel also need to be considered. Like excessive exercise, unfamiliar and/or extended transport is an environmental-related stressor, and helping your horse adapt can take time. Take it slow, especially at first, and avoid long trips whenever possible. Typically, horses that are used to travel don’t mind being on the road, but others might not be so adaptable. Either way, take steps to keep your horse healthy at home and while you’re away so he’s better equipped to handle stress.

Feed and water – quality and frequency

Horses require a lot of water – about 5–15 gallons per day. Water is required for digestive, metabolic, respiratory and thermoregulatory processes, and access to quality drinking water is crucial for maintaining GIT health. Ensuring availability during or after transport, or following prolonged exercise, needs to be a primary concern. In addition to water, quality electrolyte solutions may also need to be used.

After water comes access to quality forages, followed by concentrates to provide energy and other nutrients. Feedstuffs provide nutrients to horses and to the GIT microbiome. Abrupt changes in diet, especially sudden increases in grain or fat, negatively disrupt the GIT microbiome, resulting in dysbiosis than can be accompanied by leaky gut. Changes should be gradual and used in association with dietary sources of butyrate and an effective probiotic.

Several plants commonly found in pasture and hay can cause damage in the mouth and GIT. These include grasses such as foxtails, needle grasses, squirrel tail, bristle grass and others. Ingestion of foreign bodies, such as sand, can also be a cause of damage to intestinal cells. Injury to the mucosal lining of the GIT results in areas of inflammation which can lead to a lack of appetite, disruption of barrier function and leaky gut. Pasture and hay may also contain toxic plants that cause severe gastroenteritis. Pastures need to be well maintained and hay quality should be assessed before feeding.

Pathogens also enter the GIT during feeding. While the acidic environment of the stomach destroys many of these pathogens, some escape and enter into the intestinal system. Pathogenic bacteria and yeast may proliferate within the GIT and produce toxins. Toxins can damage the GIT resulting in destruction of cells, compromising the tight junctions between cells, inflammation of the intestinal wall and increased barrier permeability.

Systemic anti-inflammatory and antimicrobial medications

These types of medications may be necessary and life-saving but often result in a disruption of GIT barrier functions. Some anti-inflammatories are very disruptive to barrier functions in the stomach and colon, and most should not be used for more than a few days. Many of the most commonly used anti-inflammatories (NSAIDS) can lead to intestinal lesions (ulcers), some of which can become severe. Antimicrobials do just what they are intended to do – kill microbes. But not just systemically or in local tissues, they also impact the microbiome of the GIT resulting in death of both beneficial and pathogenic microbes and altering the microbial population. When systemic antimicrobials are used, it is important to supplement the diet with butyrate, to maintain barrier function, and probiotics to replace the loss of beneficial GIT microbes.

Stress is not avoidable. But leaky gut associated with stress can be prevented by good nutrition, quality oral supplements that may include butyrate and probiotics, and attentive management of the stresses to which your horse is exposed.