Study Evaluates Effects of Probiotics for Horses

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.

Another study evaluated two probiotic pastes containing "various combinations" of L. acidophilus, L. faecium, L. casei, L. plantarum, and Streptococcus faecium; neither paste had any effect on salmonella shedding in horses admitted to an equine hospital for colic, he said.

Moving forward, Furr said that scientists have investigated P. acidilactici and S. boulardii use as probiotics in other species and have achieved favorable results. P. acidilactici is a fermentative bacterium known to colonize many species' digestive tracts. S. boulardii, a nonpathogenic type of yeast, has been used to treat diarrhea in humans for many years, he said.

He said scientists have investigated using P. acidilactici and S. boulardii as probiotics in other species with favorable results. Researchers have also studied P. acidilactici and S. boulardii in horses, although not extensively. In one study of horses with naturally occurring diarrhea, Furr said, S. boulardii appeared to reduce the median number of days the horse had diarrhea from seven to five. And Furr said researchers performing a preliminary clinical study of a small number of horses reported nonspecific health effects, including improved fecal consistency.

Armed with this information, Furr and colleagues decided to test the effects of P. acidilactici and S. boulardii on equine immune function parameters. Furr said their in vitro (in the lab) results demonstrated that a particular type of white blood cell found in horses responded to the probiotic organisms’ secretion products.

Next, Furr said, the team employed 12 horses to test the same probiotic combination in vivo (in the live horse) for 72 days. He said that he and colleagues “observed effects on some specific factors of immune function response. Understanding in which clinical conditions these effects might be most useful is the next important step.”

Furr said he and colleagues are trying to put together additional studies and are specifically interested in examining the organisms’ effects on parasite clearance. In the meantime, however, he 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.

“Probiotics are not replacements for vaccinations, antibiotics, and dewormers when appropriate, or good veterinary advice,” Furr stressed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.