Endocrine-disrupting chemicals (EDCs) in a horse’s environment could play a role in the development of equine metabolic syndrome (EMS). This finding, made by Morris Animal Foundation-funded researchers, could explain some of the variability in EMS severity that can’t be explained by other commonly measured factors, such as diet, exercise, and season.

“This is a pivotal piece of a very complicated jigsaw puzzle,” said Molly McCue, DVM, MS, PhD, Dipl. ACVIM, professor and interim associate dean of research in the University of Minnesota College of Veterinary Medicine, in St. Paul. “There are a lot of horse owners out there who are very diligent about providing their horses fantastic care, but the horse is still diagnosed. It’s important to be aware that these chemicals contribute to the problem so we can look for ways to reduce horses’ exposure to them.”

The team studied more than 300 horses from 32 farms in the United States and Canada. They focused on Welsh ponies and Morgan horses, as these breeds are more likely to develop EMS than others. The team collected data on the horses’ lifestyles, including diet, exercise, and past illnesses, as well as their farm location.

Researchers also examined blood plasma samples from the horses and looked for EDCs that have effects on estrogen and aryl hydrocarbon receptors. Simultaneously, they determined whether an individual horse had blood test results consistent with EMS (including evaluating insulin and glucose levels at rest and following a sugar challenge). Finally, they analyzed the results to look for correlations between plasma EDC concentration and these variables