Non-invasive screening for treatment of heifers with the anabolic steroid melengestrol acetate (MGA) by feces analysis

For eight weeks, two heifers each had been orally administered daily doses of 0, 1.5, or 5 mg melengestrol acetate (MGA) in a feed premix. Four heifers received the labeled dose of 0.5 mg/day. Regular feces samples were taken throughout the experiment. A rapid screening method for the determination of MGA in feces was developed, consisting of liquid extraction, clean-up on solid-phase extraction cartridges and quantification by enzyme immunoassay (ELISA). Residues in feces were dose-dependent with mean values of < 0.25, 2.0, 4.4, or 15.4 ng/g for 0, 0.5, 1.5, and 5 mg/day doses, respectively. In contrast to urine analysis, feces analysis appeared to be a suitable means of non-invasive screening before slaughter for surveillance of MGA treatment and verification of its compliance with labeled dosage.