Evidence that probiotics can be used to control gastrointestinal diseases in horses is currently weak, according to researchers.
Scientists from Switzerland, Denmark and Canada have carried out a review of evidence relating to their effectiveness, the findings of which have been published in the Journal of Veterinary Internal Medicine.
Angelika Schoster, Scott Weese and Luca Guardabassi said they considered the aim of developing one probiotic to aid in the prevention or treatment of all diseases in horses was unrealistic.
“Each bacterial strain has different effects,” they said.
“The choice and combination of strains for a therapeutic formulation needs to be specific for each disease and should be based on the in vitro properties of the strains.
“Randomized placebo-controlled clinical trials under controlled conditions then are necessary to provide evidence for each probiotic formulation in horses.”
Use of over-the-counter products was questionable, they concluded, based on what they assessed as a lack of regulation regarding quality control of commercial products. This was particularly so in the absence of scientific information on safety and clinical effectiveness.
“Efficacy trials should be conducted and published in peer-reviewed journals before recommending use,” the trio suggested.
“These products also should be carefully evaluated for their composition and concentration by the investigators of the clinical trials to ensure efficacy and reproducibility of results.”
Despite these limitations, probiotics were generally regarded as safe, cost effective and easy to administer, they said. However, some evidence for potential negative effects in foals exist.
“Therefore, additional research is warranted to test possible applications in equine veterinary practice.”
The focus of probiotic research should shift from currently used agents to species that were more abundant in the intestinal microbiota (the gut microbes) of the horse, they said.
Such research should exploit new knowledge of the composition of the equine microbiota, and particular emphasis should be given to bacterial species associated with the microbiota of healthy horses, they suggested.
The approach of administering one, or a few strains together, should be rethought, they said, based on the background on the vast microbiota.
“Given the promising results of fecal microbiota transplantation in humans, the clinical efficacy of this approach should be tested for prevention and treatment of enterocolitis in horses,” the trio suggested.
Schoster, who is with the Clinic for Equine Internal Medicine at the University of Zurich, and her colleagues said gastrointestinal microbiota was extremely important for human and animal health, with investigations into its composition and therapeutic modification receiving growing interest in human and veterinary medicine.
Probiotics, they said, were a way of modifying the microbiota and have been tested to prevent and treat diseases.
But, despite their widespread availability and use, scientific, peer-reviewed evidence behind commercial probiotic formulations in horses was limited.
They said that although promising results had been achieved in laboratory-based studies, benefits in horses themselves have been more difficult to prove.
“Whether the ambiguous results are caused by strain selection, dosage selection or true lack of efficacy remains to be answered.”
Although these limitations existed, probiotics were increasingly being used because of their lack of severe adverse effects, ease of administration, and low cost, they said.
However, they concluded: “Although probiotics have shown promise in the treatment of selected diseases in humans, the evidence that they can be used to control gastrointestinal diseases in horses so far is weak.”
Weese is based at the Department for Pathobiology at University of Guelph in Canada, and Guardabassi at the Faculty of Health and Medical Sciences at the University of Copenhagen in Denmark.
Schoster, A., Weese, J.S. and Guardabassi, L. (2014), Probiotic Use in Horses – What is the Evidence for Their Clinical Efficacy?. Journal of Veterinary Internal Medicine, 28: 1640–1652. doi: 10.1111/jvim.12451
The full review can be read online here.