The Truth about Supplements: Equine Probiotics and Prebiotics

Supplements are always a hot topic in the barns. They are generally very available, inexpensive and easy to administer. Many supplements offer quick fixes for complex problems, such as preventing colic, halting the progression of joint disease, immune support, etc. After all, we all just want the best for our horse and these supplements all promise such great benefits and they are seemingly harmless so why not?

The most commonly used nutritional supplements are for joint disease and the second most commonly used supplements are for digestive health. Digestive health is a key component to overall equine health. So, I guess that explains why Smartpak has at least 25 different digestive support supplements and Valley Vet Supply has about 84. These supplements are overwhelming to compare and contrast. Smartpak has this nifty comparison tool that helps. But, I, the perpetual skeptic, keep going back to this question: How do I know that the claims these supplement companies are making are substantiated??


This is a nifty little comparison tool, thanks Smartpak.

Most digestive support supplements contain some blend of herbs, enzymes, amino acids, and prebiotics/probiotics. This post is going to focus specifically on probiotics and prebiotics. The basis behind using a prebiotic or probiotic is that there is a delicate balance of bacteria naturally present in the equine GI tract. These microbes help to break down the food particles and also combat “bad bacteria” for space. So, in theory, supplementation could help improve digestibility, improve GI immune function, help treat diarrhea, and maybe even help prevent colic.

bacteria 2

The difference between prebiotics and probiotics

Prebiotics are food for the “good bacteria”. They are most commonly carbohydrates or long chains of sugars, such as fructooligosaccharides, xylooligosaccharides, manooligosaccharides (MOS), pectin and psyllium.

Probiotics are the actual “good bacteria” themselves. They must meet three requirements to be considered a probiotic. 1.) They must be alive, 2.) Contain a taxonomically defined microbe, 3.) Be safe for intended use. The most common types of probiotics in horses are Lactobacillus, Bifidobacterium and the yeast Saccharomyces boulardii.

good bacteria

Do they actually work?

You would think that if there are that many different prebiotic/probiotic products out there…there must be tons and tons of scientific literature to support its use. But that is not the case. Despite the popularity of these products, the scientific evidence supporting their use is quite minimal.

Martin Furr, DVM, PhD, Dipl. ACVIM, described a preliminary study evaluating the effects of using Pediococcus acidilacticiand Saccharomyces boulardii-based probiotics in horses, in an article by The Horse. He said “scientists have investigated using P. acidilactici and S. boulardii as probiotics in other species with favorable results. Researchers have also studied P. acidilacticiand S. boulardii in horses, although not extensively.” In a study of horses with naturally occurring diarrhea, S. boulardii to reduced the median number of days the horse had diarrhea from seven to five and fecal consistency had qualitatively improved. Preliminary research by Furr demonstrated in vitro (in the lab) results demonstrated that a particular type of white blood cell found in horses responded to the secretion products of P. acidilactici and S. boulardii. Furr continued to offered some advice for owners: “In general, it appears that the available probiotic compounds are safe and unlikely to cause any problems; however, it remains unclear how useful they are overall. Further, the term ‘probiotic’ is very general, and there is likely to be a lot of difference between various products which use different organisms.

A study done in 2008 by K.L. Swyers et al. found that supplementing equine diets with direct fed microbials (DFM) (a..k.a. probiotics) had minimal effects on digestibility and acidosis. Another study in 2008 by Respondek at al. described that prebiotics effectively reduced the disruptions in hindgut bacteria during a stressful event such as acute starch overloads.   hhhmmmm……..

Which Supplement is Best?

Use caution when selecting your nutritional supplements. Unlike drugs, these “neutraceuticals” are not required to undergo any quality assurance measures or current Good Manufacturing Practices. Basically this means that what is inside the package may or may not be wheat is on the label. That is pretty scary to me, I kinda like to know what I am putting into my horses body.

Although it might seem like we can take the approach “We don’t know if it helps, but it can’t hurt” but studies have shown that probiotics can actually have a detrimental effect on your horse. A study by Weese et al. in 2005 showed that foals receiving Lactobacillus pentosus WE7 had a higher incidence of diarrhea. This proves that there can be detrimental effects of probiotics.

The take home message:

  • If you feel strongly about using prebiotics or probiotics as a way to improve equine digestive function, look for a product containing S. boulardii because there is at least some evidence that this is helpful.
  • Select a product with a guaranteed analysis (GA) or GMP certification to help ensure that the content inside the container matches the product label.
  • Don’t hesitate to ask your veterinarian for help and guidance when selecting supplements for your horse.

My Two Cents: 

If you ask me my personal opinion I will tell you to KEEP IT SIMPLE. Feed your horse good quality forage. I love this post by Dr. Ramey about “The Color Green and Gut Bacteria”. He sums up all of the research that shows you exactly where and how your horse naturally gets vitamins and minerals.Turn your horse out on a good quality pasture and provide good quality forage when pasture is unavailable. If needed, supplement your horse’s diet with a balanced feed, and always provide a salt block. That is all you need. SIMPLE as that.

I see the potential in the use of prebiotics and probiotics in our horses. Research work in the laboratory says that it can have great benefits, and I believe that. But in my opinion, I would not spend money on a pre/probiotic supplement for my horse until somebody can prove to me that the strain of bacteria in that product is actually legitimate and has positive benefits. Until then, I will spend that money on riding lessons because out of all of my horsey expenses (veterinary, basic care and farrier aside) those give me the most bang for my buck.

Healthy horses and happy riding!


Desrochers AM, Dolente BA, Roy MF et al. Efficacy of Saccharomyces boulardii for treatment of horses with acute enterocolitis. J Am Vet Med Assoc. 2005; 227:954-9.

Respondek F, Goachet AG, Julliand V. Effects of dietary short-chain fructooligosaccharides on the intestinal microflora of horses subjected to achange in diet. J Anim Sci 2008; 86: 316-23.

Swyers K, Burk A, Hartsock et al. Effects of direct-fed microbial supplementation on digestibility and fermentation end-products in horses fed low-and high-starch concentrates. J Anim Sci 2008;86:2596-2608.

Weese JS, Rousseau J. Evaluation of Lactobacillus pentosus WE7 for prevention of diarrhea in neonatal foals. J Am Vet Med Assoc 2005;226:2031-4.

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