General Medicine: A Review of Probiotics

The definition of probiotics was refined in 1998 to “living microorganisms, which upon ingestion in certain numbers, exert health effects beyond inherent basic nutrition.” Probiotics have been increasing in popularity due to their ability to reduce the use of antibiotics, their degree of safety, and an increase in the public’s desire for more natural products. In “A Review of Probiotics: Are They Really Functional Foods?” Scott Weese, DVM, DVSc, Dipl. ACVIM, of the University of Guelph in Ontario, Canada presented the history and basic concepts of probiotics for use in human and equine medicine.

In horses, it is thought that probiotics might be most useful in the prevention and treatment of antimicrobial-associated diarrhea, treatment of Clostridial colitis, salmonellosis, and other types of acute diarrhea, treatment of chronic diarrhea, prevention of nosocomial diarrhea, and prevention of acute infectious (especially rotaviral) diarrhea in foals.

Weese said that certain probiotics might be effective in the treatment or prevention of certain conditions; however, all probiotics will not be effective for all conditions. Knowing the properties of the various products is important when trying to determine when to use them. Unfortunately, there is little information on what is effective in the horse or what dosage should be used. Assumptions cannot be made from human medicine, nor from research done on other species--some of these probiotics will react differently in the equine system, and some might not have any effect at all.

Several problems associated with probiotics include the lack of regulation, the lack of efficacy studies, and poor quality control. These problems make it difficult to determine dosages. Determining the appropriate dose is critical for ensuring that colonization of the organism has taken place, so that a beneficial effect can be seen. Dosage amounts have yet to be determined for horses. Also, dosage will probably vary for compromised versus healthy horses. In addition, sometimes the dose required might be impractically high, meaning that a horse would not be able to ingest that much. Therefore, the search for equine-origin organisms continues since using a species-specific organism might produce better results rather than extrapolating from research in other species.

Since no studies have shown probiotics to be effective in horses as of yet, it is difficult to make specific recommendations. If a probiotic is to be used, Weese recommended that organisms that have been shown to be effective in other species would be preferable. These include Lactobacillus acidophilus, Lactobacillus rhamnosus, and Lactobacillus casei. However, because probiotic effects are specific to individual strains in these species, it is impossible to determine whether they will have a chance at being effective without equine research. Dosing of these organisms is unknown, however Weese recommended that horses should be fed at least 10-100 billions of bacteria per day. Research is ongoing to identify specific probiotic strains that possess beneficial properties Organisms must:

  • Be able to survive transit through the acidic environment of the stomach and resist bile digestion;
  • Be able to adhere to intestinal epithelial cells, colonize the intestinal tract, produce an anti-microbial factor; and
  • Be non-pathogenic.

Other desirable traits include the ability to modulate the immune system and decrease local inflammation. Above all, probiotic organisms must be show to have a beneficial effect in horses, not just in a laboratory.

To be considered a viable commercial product, a probiotic should be shown to be safe, have no undesirable effects on the host, be robust enough to grow in commercial conditions, and survive processing and storage.

More studies are needed to determine the mechanism of action for a probiotic, most of which are made up of one or more lactic acid bacteria. Lactobacillus, Bifidobacterium sp., Enterococcus, Streptococcus, and certain strains of yeast have been examined. The difficulty in finding an effective organism lies in finding the individual strain that will have the desired effect.

Hopefully, future research studies will provide insight allowing for more specific selection of probiotic preparations,” said Weese. “In the meantime, an understanding of the general principles of probiotics and of their application in other species can allow the practitioner to make reasonable choices.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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