Characterising the Metabolic and Microbiological Disturbances Induced by Equine Grass Sickness

Characterising the Metabolic and Microbiological Disturbances Induced by Equine Grass Sickness
Joy Leng, Chris Proudman and Jonathan Swann
University of Reading

The gut bacteria of horses have long been associated with grass sickness since the presence of the bacteria Clostridium botulinum within the gut was first implicated in the disease nearly 100 years ago. However, there has been no research on how grass sickness affects the horse’s normal gut bacteria, aside from the identification of C. botulinum and its toxin. Here, we carried out a matched case-control study to better understand how grass sickness affects the equine gut bacteria and metabolism during the illness. A total of 40 horses were sampled over two years (2012-2013), 19 grass sickness horses, 6 hospital controls and 15 matched controls with the help of vets and Philip Leverhulme Equine Hospital, part of the University of Liverpool. Lab1

All samples collected underwent metabolite profiling using nuclear magnetic resonance (NMR) spectroscopy to assess the effect of grass sickness on the horse’s metabolism and to identify new markers of the disease. To complement this bacterial DNA was extracted from the faecal samples and sequenced to determine changes to the gut bacteria associated with the presence of grass sickness. Distinct differences were found in both of these analyses when comparing grass sickness and healthy horses. Lab4Bacterial diversity was reduced in horses with grass sickness and bacteria that utilise lactate were increased. These changes are consistent with those previously seen in equine colitis and in human inflammatory bowel disease. Metabolic analysis showed a reduction in bacterial activity within the gut of horses with grass sickness and a shift in the use of energy, often seen during severe illness in both horses and humans.

The ability of the urinary metabolites to differentiate between healthy horses and those with grass sickness was assessed using these metabolic signatures to diagnose a separate set of horses (10 healthy and 5 EGS). This analysis demonstrated that the urinary metabolic profile was effective for diagnosing grass sickness in the horse. This diagnostic signature was refined to the four principle urinary metabolites altered in horses with grass sickness (hippurate, 4-cresyl sulphate, trimethylamine-N-oxide and O-acetyl carnitine). This refined model had a good ability for distinguishing ill horses from healthy ones.

This research furthers our understanding of how grass sickness affects the horse and the bacteria that resides within its gut. It is one of the very few research projects applying these state-of-the-art techniques on horses rather than humans. Understanding the implications of this new evidence and integration of this information into a new diagnostic test is ongoing.

This study was funded by The Equine Grass Sickness Fund.