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, etiochola nolone (testosterone metabolite) and DHEA (testosterone precursor) in femal e bovine urines after testosterone enanthate administration was carried out . An important modification in the C-13/C-12 ratio of testosterone metaboli tes was observed, such that significant differences between precursor and m etabolites of testosterone occurred until three weeks after intramuscular a dministration of testosterone enanthate, The factors influencing the C-13/C -12 of endogenous steroids were studied especially through cattle feeding a nd age. The DHEA mean delta(13)C value was found to vary between -25 and -2 6% 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 inc rease as their precursor. Moreover, we observed a clear relationship betwee n age and efficiency of misuse determination. Indeed, because of the lower concentration of natural hormones in young animals, the contribution of exo genous molecules increases significantly compared with older subjects. Cons equently, demonstration of administration is easier to achieve in calves th an in mature animals. Copyright (C) 2000 John Wiley & Sons, Ltd.