Associations between endocrine disrupting chemicals and equine metabolic syndrome phenotypes.
Authors: S. Durward-Akhurst, N. Schultz, E. Norton, A. Rendahl, H. Besselink, P. Behnisch, A. Brouwer, R. Geor, J. Mickelson, M. McCue
Journal: Chemosphere
Summary
Equine Metabolic Syndrome encompasses insulin dysregulation, excessive adiposity and laminitis risk, yet conventional factors such as diet, exercise and season account for only part of the variation observed between affected and unaffected animals, suggesting involvement of other environmental contributors. Durward-Akhurst and colleagues measured endocrine disrupting chemicals (EDCs)—compounds that mimic or interfere with hormone signalling—in plasma samples from 301 horses across 32 farms, quantifying aryl hydrocarbon and oestrogen receptor-active chemicals using TEQ (toxicity equivalency quotient) and EEQ (17β-estradiol equivalency) units. Notably, oestrogen-like EDCs (EEQ) showed positive associations with insulin and glucose concentrations both fasting and following oral sugar challenge, as well as with circulating leptin, whilst compounds measured as TEQ correlated with elevated triglycerides. Proximity to contaminated sites (superfund locations) and sex were also significant variables, with horses living within 100 miles of designated superfund sites showing lower oestrogen-equivalent burdens, and intact mares demonstrating higher EDC exposure than males. These findings represent the first evidence linking environmental chemical contamination to measurable metabolic dysfunction in horses, implying that grazing environment and chemical exposure may warrant consideration in EMS risk assessment and management strategies alongside the traditional focus on nutrition and exercise.
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Practical Takeaways
- •EMS may be influenced by environmental chemical exposures beyond traditional risk factors—consider farm location and potential contamination sources when evaluating horses with metabolic syndrome
- •Horses on farms within 100 miles of Superfund sites showed altered EDC profiles; farm environmental audits may be warranted for EMS-prone herds
- •Current EMS management focusing only on diet and exercise may be incomplete; chemical exposure reduction strategies warrant investigation as part of comprehensive EMS prevention
Key Findings
- •Endocrine disrupting chemicals (EDCs) were detectable in plasma of 301 horses across 32 farms, with TEQ levels 0.59-536.36 pg/g and EEQ levels 4.35-15,000 pg/ml
- •EEQ (estrogen receptor-active EDCs) was positively associated with glucose, insulin, and leptin concentrations, and post-oral sugar challenge responses
- •TEQ (aryl hydrocarbon receptor-active EDCs) was positively associated with serum triglyceride concentration
- •Environmental EDC exposure may explain previously unexplained variability in EMS phenotype development beyond diet, exercise, and season