Determination of the exogenous character of testosterone in bovine urine by gas chromatography-combustion-isotope ratio mass spectrometry

A new approach was developed in order to control testosterone abuse in animal production. A gas chromatographic-combustion-isotope ratio mass spectrometric (GC-C-IRMS) method was used to distinguish the exogenous character from the endogenous character of the main metabolites of testosterone (epitestosterone and etiocholanolone) in cattle urine. This method is based on a comparison between the carbon isotope ratio (C-13/C-12) of testosterone metabolites and those of testosterone endogenous precursors. After urinary steroid purification, extracts were acetylated with acetic anhydride and injected into the GC-C-IRMS system. In order to validate the method, testosterone enanthate was administered to a 4 year old cow. The C-13/C-12 isotope ratios of testosterone exogenous metabolites appeared to be significantly different to the C-13/C-12 precursor ratios and were detected until 3 weeks after the anabolic administration. These preliminary results appear to be promising for the difficult control of natural hormones in livestock.