A RIKILT yeast estrogen bioassay (REA) for estrogen residue detection in urine of calves experimentally treated with 17-estradiol

17-Estradiol is one of the most powerful sex steroids illegally used in bovine production. The objective of this study was to evaluate the application and the specificity of the RIKILT yeast estrogen bioassay (REA) for the detection of molecules with estrogenic activities in the urine of calves experimentally treated with anabolics. Four groups of six calves each received an injection of 17-estradiol intramuscularly (group B), androsterone and gliburide (group A), and testosterone (group C) molecules at different dosage for 40 days. Group D was the control. The ability of the REA test to detect estrogenic activity in urine samples from all animals was assessed. All estrogen-treated animals (group B) showed as being positive up to 7 days after administration of the highest dosage of 17-estradiol, while the other three groups showed as being negative. The identity of estrogenic molecules in the urine of group B (17-estradiol, 17-estradiol) was confirmed by gas chromatography-mass spectrometry (GC/MS). This is the first time the REA test has been applied to detect 17-estradiol in the urine of calves treated with the hormone in vivo. The technique may offer an advantageous laboratory method for the veterinary surveillance of illegal steroid use.