Gut Microbes Don't Differ Significantly Between Horse Breeds
The equine intestinal microbiome—the population of bacteria, fungi, yeast, and protozoa residing in the large intestine and cecum—could be considered its own dynamic, intricate, and powerful ecosystem thriving within the horse’s gastrointestinal (GI) system. While researchers originally thought the microbiome’s composition could be breed-specific and, therefore, had the potential to influence horse health and behavior in ways not yet realized, this didn’t turn out to be the case upon further exploration.

According to an international group of researchers led by Núria Mach, PhD, from INRA, AgroParisTech, Universite Paris-Saclay in France, “Understanding gut microbiota similarities and differences across breeds in horses has the potential to advance approaches aimed at personalized microbial modifications, particularly those involved in improving sport athletic performance.”

Intestinal microbiota has multiple roles in equine health, such as aiding in digestion and nutrient absorption, vitamin and fatty acid synthesis, protecting the horse from infectious microorganisms, stimulating the immune system, and providing energy to the horse by fermenting forage.

The magnitude of this microscopic power is further demonstrated by the fact that there are approximately one billion microorganisms per gram of ingesta in the cecum. To date, scientists have identified approximately 108 genera of bacteria in the equine gut..

“Research also shows that nondomesticated horses have more robust or ‘diverse’ (and diversity is a good thing) intestinal microbiomes than domesticated animals and that selective breeding for performance-related traits could also be selecting for different intestinal microbiomes,” Mach said.

If this theory holds true, then such breeding could alter the microorganism populations that make up the intestinal microbiome and, therefore, could affect energy production and metabolism, either positively or negatively.

To explore this further, Mach and co-workers collected fecal samples from 189 healthy horses of the following breeds:

  1. Anglo Arabian;
  2. Belgian sport;
  3. French Saddle;
  4. Hanoverian;
  5. Lusitano; and
  6. Oldenburg.

All horses resided in the same controlled environment at a riding school in France. The researchers collected fecal samples at two separate time points eight months apart to assess the stability of the horses’ microbiomes.

Despite finding some differences in fecal microbiota diversity (i.e., the number of microorganisms identified in fecal samples) between breeds, overall the authors concluded, “… breed exerted limited effects on the equine fecal microbiota.”

This seems to be, at least in part, due to the existence of a stable “core” microbiota composed of approximately 30 genera. These were consistent across all studied breeds and the two time points.

“In sum, genetic ancestry did not significantly impact microbiome structure in this study,” said Mach. “This means that no specific bacterial species currently contributing to the intestinal microbiome can serve as a biomarker for sport performance in horses.”

The study, “Inter-breed diversity and temporal dynamics of the faecal microbiota in healthy horses,” is scheduled to be published in an upcoming edition of Journal of Animal Breeding and Genetics. The abstract is available for free online.