Relationship of Hindgut Bacteria and Chronic Laminitis in Horses

Horses are hindgut fermenters. This term means that after fiber passes through the horse’s stomach and small intestine, it enters the hindgut where it is digested through the action of billions of microbes that aid fermentation.

Any change in diet can cause a shift in the bacterial population, changing the pH balance and putting the horse at risk for colic, laminitis, and other problems. Serious diseases and metabolic upsets can also cause changes in the dominance of various types of bacteria in the hindgut. To gain an understanding of microbial populations, researchers at Texas A&M University looked at types and numbers of microbes in the hindguts of ten normal horses and eight horses with chronic laminitis.

New technology has greatly expanded the ability of researchers to examine hindgut bacteria. Studies using next-generation sequencing (NGS) have discovered thousand of previously unknown microbial species that are grouped as operational taxonomic units (OTUs). Up to 96% of these OTUs can’t be assigned to commonly found bacterial groups such as the Clostridia, Streptococci, and Lactobacilli strains known to populate the hindgut.

Fecal samples from horses in the chronic laminitis group had different levels of common bacteria from those found in normal horses, and there was more bacterial diversity in horses with chronic laminitis. The bacterial communities were dominated by Firmicutes (69% in controls, 57% in laminitic horses) and Verrucomicrobia (18% in controls, 28% in laminitic horses). Also, more OTUs were observed per individual in the laminitic horses than in the controls.

The large individual variation in bacterial communities was not explained in this study, and the function of OTUs deserves further research. Data recorded in this study may provide a foundation for future investigations of hindgut bacteria and relationships to the development and progression of chronic laminitis.