Control of illegal medroxyprogesterone acetate-application in veal calves by residue analysis in adipose tissue using...

Procedures for the determination of medroxyprogesterone acetate (MPA) in adipose tissue collected at time of slaughter allowing the control of MPA application to veal calves are described. Screening radioimmunoassays after sample clean-up were sufficient for a first survey of MPA treatments in livestock herds. Validation of all positive samples was performed by two-dimensional (silica gel diol phase and RP-18 phase) HPLC/RIA immunograms. Megestrol acetate and melengestrol acetate with cross-reactivities of 31% and 0.3% respectively were clearly separated by the RP HPLC. With an absolute detection limit of 4 pg MPA/tube (90% relative binding) negative control samples did not exceed 6 pg/tube, equivalent to 6 pg/g fat in the validating method. Seventeen days after intramuscular (i.m.) injection of 24 mg MPA only 32 pg MPA/g fat were found, while i.m. injection of 60 mg MPA and a waiting period of 19 days resulted in 2700 pg MPA/g fat. After feeding two calves 20 micrograms MPA per head daily for 1 week followed by 200 micrograms MPA per head daily for 2 weeks 359 and 468 pg MPA/g fat were measured. In plasma as well as in adipose tissue more than 80% of the whole immunoreactive material was MPA itself, without indications for the presence of cross-reacting MPA metabolites as confirmed by HPLC/RIA immunograms. Based on day of slaughter ratios of accumulation of MPA from plasma into fat of MPA-fed veal calves were 52 and 72 respectively. In urine MPA was only detectable a few days after injection; as compared to a plasma concentration of 950 pg MPA/ml the amount in urine was only 37 pg MPA/ml and also 325 pg unidentified MPA-equivalents/ml.