Probiotics in Horses: Research is the Key to Unlocking Their Potential

Probiotic therapy is emerging as a popular and potentially valuable tool in the practice of human and veterinary medicine. Probiotic therapy may be useful in the treatment or prevention of a number of disorders, particularly diarrheic disease. Still, clinical application is difficult due to a lack of research in horses and questionable quality control of commercial products. Dr. Scott Weese of the Department of Clinical Studies at the University of Guelph is burning to build on his current research of probiotics in horses. His work is contributing to clearly determining the appropriate organisms, appropriate doses and conditions that are potentially treatable with probiotics.

The appealing properties of probiotics include the ability to reduce antibiotic use, the apparently very high index of safety, and the public's perception about "natural" or "alternative" therapies. The definition of a probiotic was refined in 1998 to: "living microorganisms, which upon digestion in certain number, exert health benefit beyond inherent basic nutrition". Regardless of the definition, certain criteria have been developed to evaluate the potential of microorganisms to function as probiotics. Probiotic organisms must:
" survive the acidic environment of the stomach and resist bile digestion,
" adhere to the intestinal lining,
" colonize the intestinal tract,
" produce an anitmicrobial factor and inhibit enteric pathogens (disease-causing bacteria).
Other properties such as immunomodulation, modulation of metabolic activities and the inactivation of procarcinogens are also desirable. An organism can only be considered a probiotic after these properties have been identified, and a positive health effect has been documented. Many authors say that probiotics should also be safe, result in no undesirable effects on the host (i.e. excessive gas production), be robust enough to grow in commercial conditions and survive processing and storage.

Research has evaluated the effect of dietary yeast culture on training and performance. But if a product does not contain live microorganisms it cannot be, by definition, a probiotic. Dietary yeast cultures are now being used in many commercial feeds as a means of increasing the digestible energy content of feed. However, these products are nutritional supplements rather than probiotics.

Development of probiotic products requires more than just selection of one or more lactic acid bacteria (common ones are strains of Lactobacillus and Bifidobacterium). Probiotics must be identified at the strain level and testing must be performed on individual strains. Even the probiotic qualities of yogurt depend on the numbers of viable bacteria present and the bacterial strains of lactobacilli, as not all strains have a probiotic effect. Research in human medicine has shown the strain Lactobacillus GG to be effective in the treatment and prevention of a number of problems including acute diarrhea in children, travelers' diarrhea in adults, Crohn's disease and reducing the incidence of antibiotic associated diarrhea in infants.

Labels descriptions on commercial products should be scrutinized. Appropriately labeled products should indicate the number of CFU present at the date of expiry. Extrapolating from recommendations in people, an average horse (450 kg) would likely require 10-100 billion CFU/day of an organism able to colonize the intestinal tract.

Based on existing research in other species, it seems likely that probiotics have a role in equine medicine. However, further research is required to identify organisms that possess probiotic properties in the horse's digestive tract, have clinical effect, and can survive processing and storage.

Dr. Weese has been busy evaluating the contents of several commercial products designed for both veterinary and human use. Results are in and a scientific paper is pending publication. Following this, these results will be available online at This research and a review of probiotics written by Dr. Weese will link to his name in the TEAM section.

Cutline for foal photo: Probiotics are potentially useful in the prevention and treatment of colitis and diarrhea, particularly in foals. W. Pearson photo.

Add to Scott Weese photo:

…. is taking a close look at the use of probiotics in horses.

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Updated: October 2005.