Monitoring Estra‐4,9‐Diene‐3,17‐Dione Exposure in Equine Hair

ABSTRACT

This study investigated the incorporation of estra‐4,9‐diene‐3,17‐dione (dienedione) and its metabolites into equine hair following exogenous administration and evaluates the potential application of hair analysis for long‐term doping surveillance. Mane hair samples were collected from three Thoroughbred castrated horses before and after oral administration of dienedione and from untreated colts for comparison. Dienedione was detected in post‐administration hair from all treated horses but was absent in corresponding pre‐administration samples. Segmental distribution patterns indicated contributions from both systemic incorporation via hair follicle and external absorption, such as sweat or sebum, with considerable interindividual variability. Three dienedione metabolites (M3a, M7a and M7b), previously reported to exhibit prolonged persistence in plasma and urine, were also detected in hair from the treated horses and showed similar segmental distribution. The absence of detectable dienedione and its monitored metabolites in hair from untreated colts, despite their endogenous presence in urine, suggests that hair analysis may provide more definitive information for the interpretation of dienedione findings following exogenous administration.