Nutritional supplements containing probiotics are popular purchases for some horse owners, even if not all of these products’ label claims are backed by research. But some researchers are working to better understand these probiotics’ effects on horses. At the 2013 Western Veterinary Conference, held Feb. 17-21, in Las Vegas, Nev., one veterinarian presented research behind a certain type of probiotic supplement for horses.

Martin Furr, DVM, PhD, Dipl. ACVIM, a professor and Adelaide C. Riggs Chair in Equine Medicine at Virginia Tech’s Marion duPont Scott Equine Medical Center, described a preliminary study evaluating the effects of using Pediococcus acidilactici and Saccharomyces boulardii-based probiotics in horses.

Probiotics are a subtype of immunomodulators, which are substances designed to enhance the body’s defense mechanisms. Manufacturers market these nutritional supplements to support and protect the gastrointestinal (GI) system in a variety of mammals, including horses. Furr said that while probiotics’ mechanism of action remains “poorly described,” existing research suggests they can (when consumed appropriately) have a number of beneficial effects on animals’ immune system and/or GI tract function, including:

• Reducing or preventing pathogenic (disease-causing) organisms from adhering to enterocytes (cells lining the intestines) via specific secreted factors;
• Preventing pathogenic organisms from adhering to enterocytes via competitive colonization;
• Secreting microbial compounds;
• Secreting products that degrade bacterial toxins;
• Stimulating immune responses through interaction with immune cells in the GI tract; or
• Enhancing GI barrier function.

Furr said some scientists have suggested that, to be as effective as possible, the organisms in probiotics should be host-specific so they have a greater chance at surviving in and colonizing the gastrointestinal tract.

Scientists began exploring probiotic use in horses several years ago, Furr said; however, researchers are still working to understand which organisms are best suited for equine use. One study Furr cited evaluated the effects of Lactobacillus pentosus WE7 on foals with diarrhea; unfortunately, he said, the product actually appeared to increase the incidence and severity of the foals’ diarrhea.

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