Modification of 17β-estradiol metabolite profile in steer edible tissues after estradiol implant administration Original Research Article

17β-Estradiol can be used, alone or in combination with other natural or synthetic steroid hormones, to improve weight gain and feed efficiency in breeding cattle. Approved in the USA, Canada, Argentina, Australia and New Zealand, natural hormones are strictly forbidden within the European Union. Differentiation of non-treated and anabolized animals is still now nearly impossible only on the basis of steroid residue measurement by mass spectrometry (MS). A very specific and sensitive method using gas chromatography–high resolution MS (HRMS) was developed and validated for 17α-estradiol, 17β-estradiol, their corresponding hydrophilic phase II metabolites (glucurono-, glycosido-, and di-conjugates forms) and lipoidal fatty acid esters. Muscle, liver, kidney and fat samples from control or Revalor® single or multi-implanted steers have been assayed. The results demonstrated the possibility of differentiating untreated and implanted animals on the basis of their metabolic profile, using the analysis for 17β-estradiol in fat (free and fatty ester forms) and kidney (glucuronide form), as well for 17α-estradiol in liver (free form). A multi-dimensional statistical approach confirmed the conclusions and permitted a synthetic descriptive model to be built.