Stabilizing the Horse's GI Microbiome
Health of the intestinal microbiome goes hand-in-hand with equine digestive health. Microbiome manipulation is the subject of a research article focused on ways to improve intestinal health [Song, S.J.; Woodhams, D.C.; Martino, C., et al. Engineering the microbiome for animal health and conservation. Experimental Biology and Medicine 2019. DOI: 10.1177/1535370219830075].
“Research shows that microbial dysbiosis, described as an ‘imbalance’ of the typical microbiota caused by perturbation, is often linked to negative health conditions. Dysbiosis could arise in a number of ways: an overgrowth of pathogenic microbes (or opportunistic pathogens); a depletion or absence of beneficial microbes; or an overall decrease in microbial diversity.”
Antibiotics are often incriminated in adversely affecting beneficial microbes, leading to dysbiosis and unfavorable effects on health. The report mentions that horses might develop colitis due to gut dysbiosis caused by differences in the abundance of certain microbiota rather than the differences in their presence or absence.
Supplementation with a variety of nutrients—prebiotics and probiotics—is a common strategy tried by horse owners and veterinarians to help improve equine digestive health. The use of prebiotics is intended to provide nutrients to existing beneficial microorganisms in the gut.
Probiotics are reported to help host immunity against pathogens, such as through alteration of biofilms, helping with epithelial turnover of the gut, producing antimicrobial molecules, and activating host immune responses. Further, it is suggested that probiotics might prevent colonization and proliferation of pathogens through competitive exclusion to stabilize the microbiome. These favorable effects need more evidence-based research.
One big dilemma for the use of probiotics in horses is that the organisms must be isolated, cultured and provided in a stable form that can withstand equine digestive juices. Another known problem with probiotics is that ingredients listed on commercial labels on the bucket are not always present in the product. With no FDA oversight to ensure the veracity of label claims, this problem is not likely to be overcome any time soon.
Another microbiome-stabilizing strategy that is gaining popularity in the equine industry is the use of transplantation of feces from a healthy donor.
Phage therapy—one that targets an individual species or strain of bacteria—is yet another suggested means to selectively target dysbiosis. Along similar lines, use of pyocins—phage tail-like structures that punch a hole through bacterial cell membranes to kill the pathogen—is a potential therapy. Another emerging technology uses gene editing via CRISPR-Cas, which might ultimately be applied to animal health.
More research is yet to be done in all these techniques and technology. For now, prevention of equine dysbiosis is key and relies on limiting use of antibiotics, feeding forage-based diets to horses, good biosecurity to limit the risk of infectious disease, and implementing management strategies that minimize stress in living, training, transport and competition.