An Army Inside

Your horse’s intestines are teeming with millions of friendly bacteria that could provide the key to his overall health. Richard Hepburn MRCVS explains

- Richard Hepburn

IN both human and veterinary medicine there is a growing understanding of the importance of gut microorganisms to overall health, and their role in various disease states.

This is an emerging science that is complex and rapidly evolving. In man, there is an increasing appreciation of the link between the gut microbiome (see glossary, opposite) and immunity and metabolic function. This is in addition to the alterations to this microbiome that are linked to intestinal disease such as irritable bowel syndrome, as well as obesity and metabolic disorders including type 2 diabetes. In the horse, similar changes are being identified, although equine intestinal physiology is fundamentally more complex.

The horse’s stomach and small intestine lead to the hindgut, which comprises the caecum, ventral colon, dorsal colon, small colon and rectum. Within the hindgut there are differences in the microbiota — the community of microorganisms — between these regions, with the main change occurring at the junction of the ventral and dorsal colon, known as the pelvic flexure.

The microbiota from the dorsal colon through to the rectum are very similar to those found in fresh droppings. Given the importance of the dorsal colon to fermentation of dietary fibre, this allows researchers to study the impact of changes in faecal microbiota. If this relationship did not exist, more invasive techniques would be required to sample intestinal contents.

The gut of the horse has two sets of genetic material. The genes inside the cells that make up the gut wall are inherited from the horse’s sire and dam, and remain almost stable throughout his life. In addition, there’s the microbiome, acquired from the horse’s environment and dynamic in its population.