Equus|Autumn 2020
Supplements formulated to replenish and fortify the diverse microbiome in the equine gut may help your horse stay healthy, but you’ll want to shop smart and know their limitations.
Gulsah Kaya Karasu, DVM, with Christine Barakat

Your horse’s digestive system is remarkably efficient. From grass, hay, grain, salt and water, the equine gut can extract or synthesize all the calories and nutrients necessary to keep the typical pleasure horse healthy and in good body condition. And it functions pretty much flawlessly under a wide range of conditions both internal and external.

Much of the credit for this digestive efficiency goes to the colonies of bacteria, protozoa and fungi---collectively referred to as intestinal flora---that reside within the horse’s intestines. These microorganisms are continually consuming, excreting and reproducing, as all living things do. Your horse isn’t unique in hosting this diverse and dynamic microbiota: Researchers estimate that there are approximately five billion such organisms per gram of digestive fluid in every mammalian digestive tract.

The natural activities of gut flora---breaking down certain molecules and synthesizing others---contribute to a larger, symbiotic web of essential digestive functions. Their main contribution is the breaking down of foodstuffs, such as starches and cellulose, so that the body can extract, synthesize or derive vitamins, amino acids or other vital nutrients. Meanwhile, these hard-working organisms also help keep damaging bacteria in check and toxins from the bloodstream. Gut flora are the ultimate multi-taskers.

These processes generally work so well that they are easy to take for granted, but that doesn’t mean that your horse’s intestinal flora couldn’t use a little support now and again. The biological balance of the hindgut can be disrupted by a surprising variety of stressors, including a long trailer ride, a course of antibiotics or even an unusually strenuous workout. In turn, these disruptions can contribute to minor problems such as a poor coat or general grumpiness, or more serious issues like colic and even laminitis. Your horse’s gut may be an ingeniously designed digestion machine, but there are some situations in which it may make sense to support it with a probiotic supplement.


The term probiotic, derived from the Greek words “for life,” describes dietary supplements that contain the microorganism strains that typically populate the intestinal tract.

The formal definition of probiotics, according to the Food and Agricultural Organization and World Health Organization is “live microorganisms, which when administered in adequate amounts confer a health benefit on the host.” Sometimes called “direct-fed microbials,” probiotics are designed to replenish and stabilize the natural intestinal flora in the digestive system. Simply put, probiotic supplements supply organisms to act as reserve “troops,” deployed to help those already at work in your horse’s digestive system during times of need.

Probiotics are found naturally in many foods. Yogurt, in particular, contains several common probiotic bacterial strains, and some products are fortified with additional cultures. Sauerkraut, kimchi and other fermented foods are also rich in probiotics. For horses, probiotics are delivered as powdered, pelleted or liquid feed supplements.

In addition to helping break down food into absorbable nutrients, probiotics are believed to support a horse’s health in four ways:


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Autumn 2020