Multi-residue screening of bovine urine on xenobiotic oestrogens with an oestrogen radioreceptor assay

An improved radioreceptor assay (RRA) is used for the screening of urine samples from cattle for the presence of exogenous oestrogenic anabolic compounds, e.g., stilbenes and zeranol. The method includes extraction of the hormones from urine samples with simultaneous purification using reversed-phase C18 cartridges. High-performance liquid chromatography is used to isolate the anabolics from the naturally occurring oestrogens. Fractions containing the stilbenes and zeranol are collected and subsequently analysed using the RRA with the oestrogen receptor, isolated from immature calf uteri, as a binder and tritiated 17 beta-oestradiol as a tracer. Urine samples from untreated calves and cows and samples from calves treated with zeranol-trenbolon acetate, dienoestrol or hexoestrol or samples containing diethylstilboestrol were analysed with this RRA method. Sensitivity, specificity and predictive values were calculated at different classification levels (0.4, 0.5, 0.6 and 1.0 ng/ml 'apparent' oestradiol in urine). An optimum sensitivity (89%) with a maximum specificity (95%) was reached at a classification level of 0.6 ng/ml. At this level the detection limits in urine samples are 0.5 ng/ml for hexoestrol, 0.6 ng/ml for diethylstilboestrol, 0.9 ng/ml for dienoestrol and 5.0 ng/ml for zeranol.