Despite owners trying to minimize stress in their horse’s lives, no matter what, stressors are going to exist. Some common examples include exercise, transportation, social stressors etc. This negatively impacts the equine gastrointestinal (GI) tract, and since horses have an extremely sensitive GI tract, owners are continually seeking out ways to better support it.

Dietary supplements are a popular inclusion in equine rations. Pre-, pro- and postbiotics are often supplemented in hopes of stabilizing the microbiome of the horse to maintain overall health and well-being.

Defining Pre-, Pro- and Postbiotics

Pre-, pro- and postbiotics are popular terms when it comes to gut health supplements. The World Health Organization defines probiotics as live microorganisms that when consumed in adequate amounts confer a health benefit to the host. One of the keywords in this definition is “live”. This sets probiotics apart from pre- and postbiotics.

Prebiotics differ as their role is to support the probiotics. Since probiotics are live, they of course need food. The prebiotics are food for the live microorganisms and can assist in keeping them alive. Generally, this is a fiber source. If you think about the equine GI tract, this makes sense, as fiber is fermented in the hindgut where the most significant microbial population resides.

Postbiotics are also non-living. This term refers to the compounds that remain after the horse has digested the pre- and probiotics. Often this is a mixture of both metabolites and non-living microorganisms. The potential benefits have not been fully elucidated, but it is hypothesized that postbiotics are beneficial for improvement in immune function.

When we evaluate the equine gut supplement market, there are a variety of options. Some may only be probiotics, but others may include a combination of the three compounds discussed in this article. The desired effect of these supplements is to have the live microorganisms colonize the cecum and colon to exert a health benefit.


There are a few key considerations when it comes to supplementing the horse with pre-, pro- and postbiotics. First, we need to know which bacterial or yeast strains are beneficial to the horse’s gastrointestinal tract. There has been a lot of research that investigates ideal microorganisms for humans to elicit a benefit; however, we don’t have this same information for horses. Most of the microorganisms that are used in equine probiotics are based on research that was performed in humans due to limited equine research. Unfortunately, we cannot assume that the same microorganisms are going to be beneficial in both species, as horses and humans have very different gastrointestinal physiology.

Secondly, the probiotic needs to remain alive – this includes through manufacturing, storage, and feeding. The product also must remain alive until it reaches the intended site of action – in the horse this is most often the cecum and colon.

A third consideration is the amount given. In humans, the recommendation that has been established is that a probiotic dose should contain 106 to 108 CFU/g (colony-forming unit per gram) at the point of consumption. This guideline has not yet been established for horses, but it is estimated that the ideal dose is at least this amount.

There have been a significant number of studies over a 19-year period that have evaluated the label claims of equine probiotic products. Unfortunately, when actual contents have been compared to label claims, large discrepancies have been found. Research is limited, and it can be difficult to determine which pre-, pro- and/or postbiotic supplement is ideal for your horse. If you want to try one of these supplements there are key aspects you can look for to increase the chances that the supplement you are purchasing is what the label claims.

1) Storage Instructions

If the product you are looking at contains a mix of pre-, pro- and postbiotics, then there should be storage instructions included on the label. These instructions are required as the customer needs to be able to ensure that the live microorganisms remain viable until they are consumed by the horse.

If you think about how most equine supplements are stored, it is often in a barn that is not temperature-controlled. This can negatively impact the viability of the microorganisms if they are exposed to varying temperatures and humidity levels. Nothing lives forever, therefore in addition to storage instructions, an expiry date is required to give the customer a better idea of how long the product is viable.

2) Strain Specification

There are a plethora of bacteria and yeast strains that can be included in probiotic supplements. When comparing products, ensure that the label includes the specific strain. An example is “Enterococcus faecium” instead of simple claims such as “probiotic blend” or “lactic acid-producing bacteria”. If you are investing in a product and feeding it to your horse, then of course you should know what is in it.

3) Dose Amount

A final piece of information that the label should include is how much you are getting of the live microorganisms. For probiotics, the amount will be given in colony-forming unit (CFU) per gram of product. A good example would be lactobacillus fermentum – 10,000,000 CFU/gram.

Potential Dangers

Although research is extremely limited, there are some potential dangers to these types of supplements for horses. There are three published studies that evaluate probiotic supplementation in foals and in all three of the studies the supplemented foals had a greater incidence of diarrhea and required more veterinarian attention than unsupplemented foals.

When we look at the research in mature horses, often there will be no benefit shown, but also no harm shown. There are a couple of studies that were able to show benefits but overall, more research is required to determine ideal supplemental strains, ideal amounts, and safety of using these products.

To conclude, our knowledge is limited and additional research is required prior to being able to be confident in pre-, pro- and postbiotic supplementation. However, if you are currently feeding a probiotic-based supplement, check the label claims and see if the company is supplying you with all of the necessary information.