Equine metabolic syndrome, a common equine condition, often proves difficult for veterinarians to diagnose and treat. Recent UF/IFAS research into genetic factors contributing to the disease provides guidance on how to manage horses so owners can prevent the disease.
The syndrome, also known as EMS — is a serious disease. It’s a collection of clinical signs including obesity, difficulty regulating blood sugar, high blood insulin concentrations and sensitivity to carbohydrates in the diet. It is the leading risk factor for laminitis, commonly known as foundering, which is noted as a common reason for euthanasia in horses by the American Association of Equine Practitioners.
“Clinically, we don’t have a great consensus for what defines abnormal versus normal factors for diagnosing EMS,” said Samantha Brooks, UF/IFAS associate professor of equine physiology. “The condition is defined as many shades of grey. Every horse is unique, and their environment is, too. We need more research to better define the disease and what is normal versus what is dangerous. This research used new methods to give us fresh clues to the mystery that is EMS.”
One of the tests used to diagnose the disease is a glucose tolerance test, similar to the test pregnant women take to diagnose gestational diabetes. The veterinarian administers a syrupy high glucose, or sugar, solution to the horse and takes blood samples over the course of several hours. This procedure is expensive, time intensive and, for horses that have EMS, it can be tricky to administer safely.
“The tests to diagnose this disease that are considered to be the gold standard are not easily done,” Brooks said. “This includes several types of glucose-tolerance tests. It is expensive, and for some of these horses, a test that gives a huge dose of sugar might not be without risk.”
“Obesity is one of the key signs of EMS,” said Laura Patterson Rosa, animal science recent PhD graduate and lead author of the study. “Obesity is not the only sign, nor the hallmark of this condition, but is present in most cases. Likewise, not every horse with obesity has EMS. In our study we were able to separate out individual metabolites, or small chemicals in the blood that are ‘by-products’ of the metabolism. Some of these metabolites were correlated more uniquely to obesity, rather than the cluster of signs that define EMS. Since these two conditions are related, and often are seen together, we need better diagnostics to help specifically distinguish EMS. This research hopes to not only provide new diagnostics, but also improve our understanding of the basic biology behind why EMS happens.”
What the research found
For this study, researchers tried an entirely new approach combining analytical chemistry to examine the metabolite markers found in the blood, along with thousands of genetic markers to look for regions of the genome correlating to those metabolite markers. Four locations in the genome stood out in the research, and any or all of them could lead to targeted prevention of EMS.
“Identifying these metabolites, as well as the genetic factors influencing them, as a way to figure out their role in EMS was a bit like working a jigsaw puzzle backwards in order to find that one key piece,” said Brooks. “My favorite region of the genome that we’ve correlated to metabolite markers for EMS contains two genes previously linked to obesity and body weight traits in cattle, humans and mice.”
Based on their molecular weight, one specific metabolite identified might be linked to how horses metabolize their plant-based diet, or they could indicate liver damage in severe cases of EMS. If the metabolite is plant-related, diets could be adjusted to shift the horse away from some of the metabolic pathways that contribute to their obesity. If instead this metabolite indicates a liver problem this could be a valuable clue to how veterinarians might treat this disease. Additional work is needed to positively identify this particular metabolite.
These small metabolite markers could be easily identified in a blood sample. This would eliminate the need for the previous lengthy glucose testing and simplify diagnosis to a one-time blood draw that could indicate the metabolic state of the animal.
“The idea that you could get a snapshot of EMS severity in a one-time blood draw is really appealing and would be a significant improvement in what we have for diagnostics now,” said Brooks. “If we can identify what this particular molecular weight compound is, we might also know where we get off-track with the horse’s health and end up down to road to dangerous EMS.”
Understanding that obesity is a key element of the disease and managing the weight of the horse is key to prevention of EMS. Approximately two-thirds of horses are obese, according to a U.K. study. Obesity is common in horses for the same reason it is in people.
“We don’t participate in physical labor the way we did 100 years ago, and we have improved diets that are designed to meet all of our needs,” said Brooks. “Also, we have easily accessible, and tasty, junk food and treats. This all contributes to problems with obesity and maintaining our blood sugar, for both horses and humans.”
“The most surprising discovery was that some of genes correlating to EMS and obesity are related to perception of smell and bitter taste,” said Rosa. “We all know horses with specific flavor preferences, especially for treats, and perhaps it is their perception of individual foods that is altering their feeding behavior and putting them at risk for EMS. It was extremely interesting to see sensation genes correlated to EMS and obesity.”
Researchers hypothesize that natural variations in these genes might lead to horses preferring sweeter feeds, or even that it may cause a lack of distinction and indiscriminate feeding behavior, ultimately contributing to overeating and obesity.
The Arabian breed as a model for genetic research
The study specifically utilized genetics of Arabian horses. Focusing on Arabians provided a relatively controlled population with similar genetic backgrounds. The breed is also an excellent model to study because they may be more susceptible to EMS.
“Arabians are famously hardy, and it is often jokingly suggested that they can ‘survive on air,’” Brooks said. “They are resilient and easy-keeping animals that were selected to survive in the difficult conditions near the desert. As a result, we think they might have genes that make them more susceptible to obesity and EMS when kept on lush pastures and modern concentrated feeds.”
The Arabian breed has also contributed to the development of many other modern horse breeds. The chance of finding a genetic component that applies to other breeds is far higher using Arabians as the model, as opposed to studying Shetland or Welsh ponies, which are also susceptible to EMS but do not share as much genetically with other groups of horses.
The results of this study are quite promising. However, researchers need to conduct additional work including a clinical trial to validate the findings on a larger sample set of horses, including other breeds.
“If we want any future success at making a dent in this terrible disease, momentum has to come from horse owners and field veterinarians that are frustrated that they do not have the tools they need to manage EMS quickly and effectively,” said Brooks. “We need support and research funding to clinically validate the results of this study, and get new tools into the hands of veterinarians.”