WHAT is the microbiome and does it impact on your horse’s wellness and performance? Horses, as we all know, are grazing animals that have evolved to survive on high fibre grass based diets. Yet, what may be surprising to some is that horses, like us humans, are not able to breakdown and digest grass based fibre on their own.

Instead, they have developed a special mutually beneficial relationship with billions of bacterial microbes in their gut that help breakdown this fibre and convert it into material/chemicals of nutritional value. It is this microbial population that is typically referred to as the gut microbiome.

The make-up of this microbial population, i.e. what amounts of what bacteria are present, differ in the foregut (stomach and small intestine) from that of the hindgut (cecum, large and small colons, and the rectum).

In the foregut, the microbial population make-up is such that they can digest starch and sugars. Where as in the hindgut, the microbial population make-up is different and can also utilise fibrous material, such as cellulose and hemicellulose fibres, that is not digested in the foregut.

This fibrous material is typically more difficult to break down as it is found in the cell wall of plants and give the cell wall is structure and strength. Fermentation of this fibre in the hindgut results in the generation of valuable nutrients, such as volatile fatty acids (VFAs). These VFAs are absorbed across the hindgut wall, enter the bloodstream and are transported to different tissues where they are used as an energy source.

In simple terms, one can consider the bacteria in the hindgut as being made up of three major groups: (i) fibre (cellulose) fermenters; (ii) starch-sugar fermenters; (iii) bacteria that utilise lactate. For a healthy hindgut, one wants to maintain a healthy bacterial population balance across these groups. With a high fibre low sugar-starch diet, the fibre fermenting bacteria will dominate, generating nutritionally valuable chemicals and help maintain a stable environment in the hindgut.

Sudden addition of large amounts of starch or sugars, such as sudden change to concentrates or rich grass, can result in increased amounts of starch-sugar reaching the hindgut and a corresponding rapid increase in the population of the starch-sugar fermenting bacteria in the hindgut. These bacteria ferment the starch-sugar material, generating lactic acid that will contribute to acidification of the gut environment. This acidic environment will be detrimental to the fibre fermenters, whose population can drop as the number of starch-sugar fermenters increase.

The population of lactate utilising bacteria can help alleviate the situation by removing the lactic acid, helping to reduce the acidity of the hindgut. However, if the sudden addition of large amounts of starch or sugars in the diet has resulted in a rapid increase in starch-sugar fermenters that the lactate utilising bacteria may struggle to keep up.

In such a situation, the hindgut microbiome can become out of balance and can contribute to diseases/conditions such as colic, acidosis, endotoxaemia (release of endotoxins into the blood stream from some families of bacteria in the gut as they die-off), as well as weight loss, all of which will negatively impact on wellness and performance. Maintaining a healthy gut, and especially a healthy hindgut, is important and significant consideration, in consultation with your vet and nutritional advisor, should be given to the feeding regime of your horse. So go with your gut, a healthy gut!