Intestinal Microbiomes of Fit and Unfit Horses Explored

The hindgut microbiome is a mighty force within the horse’s body, playing key roles in fiber fermentation, energy production, and immunity. New research shows that the microbiome may also contribute to athletic performance and that deliberately altering the horse’s diet could improve fatigue resistance and cardiovascular fitness.^*

“Although we are still far from knowing exactly how to control the microbiome, we could eventually manipulate the microbiome through dietary strategies. We may be able to enhance or deplete certain types of microbes to naturally augment a horse’s ability to compete,” explained Kathleen Crandell, Ph.D., a Kentucky Equine Research nutritionist.

As an introductory experiment, 11 endurance horses competing in a 160-km ride were recruited to study the effect of fitness and microbiome composition. Blood and fecal samples were collected prior to, during, and following the ride. Fitness was determined based on a heart rate threshold, i.e., heart rate decreased to less than 64 beats per minute within 20 minutes of recovery at each veterinary checkpoint. Among other tests, fecal samples were analyzed to identify the bacteria present in the intestinal microbiome.

Two interesting findings reported in the study included:

1. Microbes that produce methane were found more frequently in fit individuals. Methane is not absorbed by the horse and not used as energy like short-chain fatty acids. In fact, methane is generally viewed as a waste product. These data therefore suggest that methane may exert anti-inflammatory and antioxidative effects in the gut, which could be beneficial as endurance exercise is inherently inflammatory in nature.
2. Microbiomes were more diverse in fit horses, and the microbiomes of less fit horses contained fewer bacterial species. Further, bacteria in the Lachnospiraceae family were more dominant in less fit horses than fit animals.

“Nutritional interventions aimed at decreasing Lachnospiraceae may make room for other species that could increase microbiome diversity, including bacteria that would contribute to improved athletic performance,” explained Crandell.

While research in this field is clearly in its infancy, the data generated in this study certainly provide a jumping-off point to further evaluate which components of the intestinal microbiome could contribute to fitness.

Specifically, the research team suggested that a more detailed understanding of the role of the microbiome in mitochondrial function (cellular organelles specialized in energy production) will be “instrumental in developing dietary strategies that optimize cardiovascular capacity and, therefore, athletic performance.”

One current strategy for supporting a healthy microbiome is to stabilize the pH of the hindgut, keeping it from becoming too acidic. An acidic pH negatively affects the viability of beneficial bacteria while controlling disease-causing bacteria. “EquiShure, a hindgut buffer available from Kentucky Equine Research, helps maintain the integrity of the bacterial population in the digestive tract by buffering the pH,” Crandell advised.

 ^*Mach, N., C. Midoux, S. Leclercq, S. Pennarun, L. Le Moyec, O. Rue, C. Robert, G. Salle, and E. Barrey. 2022. Mining the equine gut metagenome: Poorly-characterized taxa associated with cardiovascular fitness in endurance athletes. Communications Biology 5(1):1032.