The use of probiotic supplementation in horses is a common strategy to try to improve gastrointestinal health. Probiotics have the potential to exert favorable effects on intestinal microflora. Adherence to mucosal tissue, cells and intestinal mucus enables probiotic species to competitively exclude and displace enteropathogens, elicit immune responses and to secrete antimicrobial substances called bacteriocins.
The objective of an in vitro study conducted by Kemin Industries in Iowa was to evaluate a strain of Bacillus subtilis as an oral probiotic by examining its antibacterial activity against six different equine pathogens—Clostridium perfringens, Clostridium difficile, Salmonella typhimurium, Escherichia coli, Rhodococcus equi and Streptococcus equi [Burke, M.L.; Moore, S.A. Bacillus subtilis Strain PB6 Demonstrates Growth InhibitionToward Equine-Specific Bacterial Pathogens. Journal of Equine Veterinary Science 58 (2017) 84–88]. This Bacillus probiotic strain has demonstrated excellent results in protecting poultry against intestinal disease.
In this in vitro study, the Bacillus subtilis strain demonstrated “measurable inhibitory” activity against C. perfringens, C. difficile, R. equi and S. equi. It did not inhibit E. coli or S. typhimurium despite 20 hours of agar plate incubation.
Bacillus subtilis does not colonize the equine intestinal tract, although it is able to reside there, especially for the two days it takes to transit the hindgut. The authors speculate that this is sufficient time for spore generation of beneficial antimicrobial molecules. While this study reveals the potential for Bacillus subtilis as a probiotic application in the horse, further studies are necessary to evaluate its usefulness and efficacy in the live horse.