Probiotic Use in Horses – What is the Evidence for Their Clinical Efficacy?

Abstract

The gastrointestinal microbiota is extremely important for human and animal health. Investigations into the composition of the microbiota and its therapeutic modification have received increasing interest in human and veterinary medicine. Probiotics are a way of modifying the microbiota and have been tested to prevent and treat diseases. Probiotics are proposed to exert their beneficial effects through various pathways. Production of antimicrobial compounds targeting intestinal pathogens, general immune stimulation, and colonization resistance are among these mechanisms. Despite widespread availability and use, scientific, peer‐reviewed evidence behind commercial probiotic formulations in horses is limited. Additionally, quality control of commercial over‐the‐counter products is not tightly regulated. Although promising in vitro results have been achieved, in vivo health benefits 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 exist, probiotics are increasingly used because of their lack of severe adverse effects, ease of administration, and low cost. This review summarizes the current evidence for probiotic use in equine medicine. It aims to provide veterinarians with evidence‐based information on when and why probiotics are indicated for prevention or treatment of gastrointestinal disease in horses. The review also outlines the current state of knowledge on the equine microbiota and the potential of fecal microbial transplantation, as they relate to the topic of probiotics.

Effect of a Probiotic on Prevention of Diarrhea and Clostridium difficile and Clostridium perfringens Shedding in Foals

“…Probiotics exert their beneficial effect through several pathways, including production of antimicrobial compounds targeting intestinal pathogens and their toxins, as well as general immune stimulation and colonization resistance 6. Few studies in horses have been performed to date to evaluate the efficacy of probiotics in prevention or treatment of enteric disease 4, 7, 8. The 2 studies on probiotic use to prevent neonatal foal diarrhea failed to show a lack of significant effect of probiotic treatment 3, 9.…”

The use of Probiotics in Horses with Gastrointestinal Disease

“…Some authors (Gibson and Fuller, 2000;Saarela et al, 2000) favor host species-specific probiotics, although across-species efficacy is proved for some probiotics (Lee et al, 2000). Others (Weese et al, 2004;Schoster et al, 2014) consider that probiotic strains should be selected based on their probiotic properties tested in vitro and not their origin.…”

“…However, very low levels of viable organisms, obviously less than claimed by the label and products containing other species of organisms, were commonly reported (Hamilton-Miller and Shah, 2002;Weese, 2002b;Weese and Martin, 2011). Inadequate content of commercial probiotic formulations makes their efficacy unpredictable (Schoster et al, 2014). These studies emphasize the caution in commercial probiotic product selection, but also the importance of bacteria viability control in research studies.…”

“…These studies emphasize the caution in commercial probiotic product selection, but also the importance of bacteria viability control in research studies. When purchasing and using a probiotic product most horse owners and veterinarians believe the worst consequence of using them is their ineffectiveness (Schoster et al, 2014). However, adverse effects of probiotic administration in horses have been reported in experimental studies, although their incidence was not recorded in retrospective studies (Ward et al, 2004;Weese and Rousseau, 2005;Schoster et al, 2015a).…”

“…The number of reports on adverse effects in probiotic use in horses has to be observed considering little objective studies done on the topic. Some serious concerns have been raised, supporting the hypothesis that typical probiotic genera can act as potential reservoirs of resistance for food or gut pathogens (Gueimonde et al, 2013;Schoster et al, 2014). Most of the available data on antibiotic resistance are available for lactobacilli, which have been proven to transfer genes to different gram-positive bacteria, but also acquire resistance genes from them (Mater et al, 2008).…”