“Bowel-on-the-bench:” Proof-of-concept of a three stage, in vitro, fermentation model of the equine large intestine.

The intestinal microbiota of the horse, an animal of huge economic and social importance worldwide, is essential to the health of the animal. Understanding the intestinal ecosystem and its dynamic interaction with diet and dietary supplements currently requires the use of experimental animals with consequent welfare and financial constraints. Here, we describe the development and assessment, using multiple analytical platforms, of a three vessel, continuous flow, in vitro model of the equine hindgut. After inoculation of the model with fresh horse feces, the bacterial communities established in each vessel had similar taxonomic distribution to that of the source animal. Short chain and branched chain fatty acid (SCFA/BCFA) production within the model at steady-state was consistent with expected bacterial function although higher concentrations of some SCFA/BCFAs, were apparent relative to that of ex vivo gut content. We demonstrate inter-model repeatability and the ability of the model to capture some aspects of individual variation in bacterial community profiles. This proof-of-concept study, including recognition of model limitations, supports its future development as a tool for investigating the impact of disease, nutrition, dietary supplementation and medication on the equine intestinal microbiota. Importance The equine gut model that we have developed and described has the potential to facilitate the exploration of how the equine gut microbiota is affected by diet, disease and medication. It is a convenient, cost-effective and welfare-friendly alternative to in vivo research models.