Atmospheric Stagnation and Particulate Sedimentation as Risk Factors for Equine Grass Sickness

Background: Equine Grass Sickness (EGS) is a devastating polyneuropathy linked to grazing. While a causative neurotoxin is suspected, the environmental conditions facilitating its production or ingestion remain unknown. Objectives: To determine if atmospheric ”Saddle Points”—regions of low wind speed created by converging air flows—are spatially and temporally correlated with EGS onset, and to analyse the particulate matter (PM) fractionation within these zones. Study Design: Retrospective case-control study. Methods: EGS cases (n=48) from 2025 were matched with 48 location-controlled sites. Atmospheric data (Copernicus ERA5/CAMS) were used to identify Saddle Points characterized by wind speeds