Differentiation of boldenone administration from ex vivo transformation in the urine of castrated male horses

Boldenone is an anabolic-androgenic steroid that is prohibited in equine sports. However, in certain situations, it is endogenous or is believed to be formed by microbes in urine, and therefore, an approach for the differentiation is required. Following the identification of Δ1-progesterone and 20(S)-hydroxy-Δ1-progesterone as potential biomarkers of microbial activity, the presence of six steroids was investigated in the postrace urine of castrated male horses (geldings, n = 158). In line with endogenous findings from several other species when ultrasensitive methods are employed, boldenone was detected at low concentrations in all urine samples (27.0-1330 pg/ml). Furthermore, testosterone and androstenedione were detected in 157 samples (≤12,400 and 944 pg/ml, respectively), boldienone in two samples (≤22.0 pg/ml) and 20(S)-hydroxy-Δ1-progesterone in 20 samples (≤66.0 pg/ml). Δ1-Progesterone was not detected in any population samples analysed on arrival at the laboratory. The ex vivo transformation of boldienone, boldenone, androstenedione, Δ1-progesterone and 20(S)-hydroxy-Δ1-progesterone was induced following the storage of urine samples at room temperature for 7 days but not after refrigeration. Because the administration of inappropriately stored feed sources also resulted in an increase in 20(S)-hydroxy-Δ1-progesterone concentrations, a biomarker approach to distinguish steroid administrations was proposed. In situations where the presence of boldenone would exceed a proposed action limit, the presence of Δ1-progesterone and 20(S)-hydroxy-Δ1-progesterone would be investigated. If either Δ1-progesterone or 20(S)-hydroxy-Δ1-progesterone would exceed 50 and 100 pg/ml, respectively, for instance, then this would indicate ex vivo transformation or consumption of altered feed rather than steroid administration.