Certain strains of bacteria are known to act as inhibitors of pathogens. Bacillus subtilis PB6 is one such organism that has demonstrated efficacy against Clostridium spp., E. coli, Salmonella spp., Rhodococcus equi and Streptococcus equi. Studies in poultry and hamsters have revealed that treatment with B. subtilis has yielded significant improvements of reduced weight loss and improved weight gain, reduced diarrhea and lessened mortality rates.
Horses have the potential to develop intestinal bacterial overgrowth, enterocolitis and diarrhea, particularly when receiving prolonged antibiotic therapy. With this in mind, researchers sought to examine how the B. subtilis PB6 could influence pathogenic components of the equine intestinal tract that tend to flourish in the face of antibiotic therapy (Burke, M.L. and Morre, S.A. Bacillus subtilis Strain PB6 Demonstrates Growth Inhibition Toward Equine-Specific Bacterial Pathogens. Journal of Equine Veterinary Science, 2017, volume 58, pp. 84-88].
B. subtilis organisms don’t colonize the equine intestinal tract, but they are able to reside in the large intestines for up to two days to potentially produce beneficial effects by inhibiting overgrowth of pathogenic bacteria.
This study at Kemin Industries in Iowa was conducted in vitro, so further studies are necessary to confirm efficacy of using Bacillus subtilis as a probiotic in living horses.