How Prebiotics & Probiotics Help Your Horse

It can be overwhelming for any horse owner with the number of supplements available on the market. It has led to much confusion on which, if any, supplements to feed. It also has owners asking how they will benefit their horses. This is especially true with pre- and probiotics. Since they have arrived on the market for horses, many have asked what they are and if they even work. Fortunately, research studies are beginning to show the multiple benefits of feeding pre- and probiotics to horses.

What Is the Microbiome in the Horse?

Within the gut of animals (and humans!) resides microorganisms that help aid in the digestion of food. This environment of microorganisms is called the microbiome. The microbiome of the horse’s gut is estimated to hold over 1 quadrillion (1015) bacteria, yeast, fungi and other cell types. Bacteria is the most dominant cell type in the horse, with most of the microbiome residing in their hindgut.

For horses, the microbiome is critical in the digestion of fiber in the hindgut, where the microbiome aids in fermentation of forages (hay/pasture) and produces useful nutrients, including B-vitamins and volatile fatty acids. Further, research has shown the microbiome throughout the horse’s digestive tract has important immune system functions and can impact equine behavior and cognitive function. Thus, it is very important to ensure horses maintain a healthy and functioning digestive tract. One way to help ensure this is through the use of pre- and probiotics. Research has shown that pre- and probiotics help maintain, or even restore, a healthy population of microorganisms in the digestive tract.

What Are Pre- and Probiotics?

Prebiotics are non-living ingredients that help “feed” and maintain the beneficial microorganisms in a horse’s digestive tract. They are not able to be digested by the horse, but help nourish, maintain, and even grow the beneficial microorganisms. The two types of commonly fed prebiotics include:

  • Mannan-oligosaccharides (MOS) are non-digestible sugars that bind harmful bacteria, like E. coli, and are then passed in the feces. They help reduce the population of the “bad” microorganisms in the digestive tract, allowing the more beneficial bacteria to flourish.
  • Fructo-oligosaccharides (FOS) help to nourish and feed beneficial gut bacteria and the other microorganisms so they can prosper.

Conversely, probiotics are living bacteria and yeast that help repopulate the gut of the horse with beneficial microorganisms. These have also been called direct-fed microbials. Because the hindgut of the horse and its microbiome can be disrupted rather easily due to a variety of causes, studies have shown feeding probiotics to horses can be beneficial to their overall gut health. Commonly fed probiotics include:

  • Saccharomyces cerevisiae: a live yeast with research that has shown to help in improving fiber digestion, especially with lower quality grass hays. Other benefits have been identified, such as improved phosphorus absorption and improved growth rates in foals.
  • Live bacteria: many species of bacteria have been fed, including strains of Lactobacillus, Bifidobacterium and others. Research on their benefits is still ongoing, but they are believed to be the beneficial microorganisms in a horse’s hindgut.

How to Feed Prebiotics and Probiotics

While you can feed prebiotics and probiotics separately to your horses, it is generally recommended to feed them together. The thinking behind this is that they work synergistically and when fed together, they maximize your horse’s digestive health.

While pre- and probiotics can be fed either together or individually as a top dress with a horse’s feed, today that is no longer necessary. With the improvement of feed formulation and manufacturing, many top-quality horse feeds now include pre- and probiotics in their formulation. For example, all Tribute® feeds have the addition of Equi-Ferm XL®, which is a microencapsulated (protected) pre- and probiotic that is designed to help aid in fiber digestibility and maintain or improve overall gut health. However, if a chosen horse feed does not have the addition of pre- and probiotics, it is still acceptable to top dress feed with a pre- and probiotic.

When evaluating which pre- and probiotic to feed your horse, it is critical they are microencapsulated. Because horses are hindgut fermenters, all feed must first pass through the highly acidic stomach and long small intestine before arriving in the cecum (or hindgut) for fermentation. Any pre- or probiotic that is not encapsulated will not survive the stomach. Thus, any potential benefits to the rest of the digestive tract are lost.

Which Horses Benefit from Prebiotics and Probiotics?

Generally, any horse will benefit from the addition of pre- and probiotics to their diet. Because the horse’s digestive system is sensitive to change, consistently feeding pre- and probiotics can help reduce chances of digestive upset.

Specifically, the horses most likely to benefit from pre- and probiotics are our young and aged horses, as well as those under stress, like high performance horses. The reasoning is:

  • Young horses generally do not have a full and stable population of microorganisms in their gut.
  • Aged horses are less efficient at digesting their feed and need help to maintain their microbiome.
  • Stress can lead to disruptions in hindgut health and the microbiome.

Finally, any horses that have been treated with antibiotics should be fed pre- and probiotics. Antibiotics can often kill off beneficial gut bacteria and it is important to help reestablish healthy populations.


It is generally accepted that pre- and probiotics are beneficial to all of our horses. As more research emerges, it is clear that these supplements are playing a vital role in maintaining the digestive health of horses. If you have any questions about your feeding program, please contact us for a free, personalized feeding plan!

Article By: Chris Mortensen, Ph.D.
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