A way to improve or resolve a condition or diagnosis. This might include resolving the underlying cause or treating the signs of disease (symptomatic treatment).

Cost: Under $100

These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.

YOUR VET MAY Recommend

Probiotics & Prebiotics, Commercial

Cost: Under $100

These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.


A probiotic is an intentionally fed source of live microorganisms (bacteria or yeast), that is intended to benefit the health of the recipient by populating or repopulating the intestine.

The intentional addition of “good” microorganisms is supposed to reduce the “bad” population of organisms. In addition to inhibiting pathogens, probiotics may affect the immune system and metabolic activities to promote overall health.

In contrast, a prebiotic fosters the health of “good” microorganisms that are already present in the gut by providing supportive nutrients for their growth.

In horses, probiotics may be used in cases of diarrhea or other forms of GI upset. They might also be helpful in the prevention of GI upset during periods of antibiotic use and stressful events (hospitalization, weaning, traveling, etc.). It might even be fed on a daily basis.

Unfortunately, much of the evidence for the use of probiotics is based on studies done on humans and other animals, not horses. When a micro-organism is not a native inhabitant of the horse, and studies have not been performed in equines, we should remain skeptical of the effectiveness of this treatment.

The most promising studies in the horse are based on trials with yeast (saccharomyces cerevisiae and Saccharomyces boulardii). They were shown to reduce the severity and duration of diarrhea in hospitalized horses and protect against starch overload from grain feeding.

Studies based on lactic acid bacteria (Lactobacillus, Bifidobacterium and Streptococcus) are less promising. One study shows a benefit in preventing Salmonella shedding or reducing diarrhea and another found a strain (L. pentosus) that was harmful in foals.

Due to potential quality and safety issues, you should consult with your vet when considering the use of probiotics or prebiotics.

Independent testing performed to verify the contents of several commercial probiotics has yielded poor results for the veterinary brands.

my vet's role


Probiotics and prebiotics are classified as dietary supplements, not drugs. This means that these products are not regulated by the U.S. Food and Drug Administration (FDA). Therefore, testing for safety, quality, and consistency of these commercial products are not required, which raises some concern.

Poor quality products are available that contain few beneficial organisms and may cause harm.
Many products contained few live organisms, some contained strains not listed on the label or strains not reported to have any benefit, and a few even contained potentially harmful bacteria. Another study performed on an equine specific probiotic isolated bacteria of concern to human health.


your role

Is it working? Timeframe for effect.
Evaluating the efficacy of this treatment is difficult. If a horse improves after the administration of one of these products, the question is whether they would have improved on their own, or whether a different treatment was responsible for the improvement.
Questions To Ask Your Vet:
  • Should I expect to see a difference when I use these products?
  • Are there particular products you use or recommend?
  • How can I assess the effectiveness of this treatment?

further reading & resources

Author: Coauthored by Doug Thal DVM DABVP & Susan Shaffer DVM