Characterization of exogenous testosterone in livestock by gas chromatography/combustion/isotope ratio mass spectrometry: influence of feeding and age

The detection of exogenous testosterone in bovine urine was investigated by using gas chromatography/ combustion/isotope ratio mass spectrometry (GC/C/IRMS). The carbon isotopic ratio measurement of epitestosterone, etiocholanolone (testosterone metabolite) and DHEA (testosterone precursor) in female bovine urines after testosterone enanthate administration was carried out. An important modification in the C-13/C-12 ratio of testosterone metabolites was observed, such that significant differences between precursor and metabolites of testosterone occurred until three weeks after intramuscular administration of testosterone enanthate, The factors influencing the C-13/C-12 of endogenous steroids were studied especially through cattle feeding and age. The DHEA mean delta(13)C value was found to vary between -25 and -26% when hay and concentrate diet were used for fattening. On the other hand the delta(13)C value observed when maize silage was used increased to -20 parts per thousand. Testosterone metabolites showed the same delta(13)C increase as their precursor. Moreover, we observed a clear relationship between age and efficiency of misuse determination. Indeed, because of the lower concentration of natural hormones in young animals, the contribution of exogenous molecules increases significantly compared with older subjects. Consequently, demonstration of administration is easier to achieve in calves than in mature animals. Copyright (C) 2000 John Wiley & Sons, Ltd.