When residues of nortestosterone (NT) were found in the urine of cattle, racehorses or bodybuilders, exogenic administration was thought to be proven. In previous literature, no records were found of the endogenic presence of this molecule. In the horse-racing world, Houghton and Courthot found that NT is normally present in the urine of the stallion. Belgian and Dutch researchers found that NT is also present in the urine and edible parts of the intact boar. Vandenbroeck et al. (1991) suggested the endogenous presence of NT (in the beta form) in the pregnant cow. Meyer (1992) reported the presence of NT (in the alpha form) in relatively high amounts in the urine of the cow peri-partum and the neo-natal calf. These observations may have important consequences for veterinary meat inspection in the EU. Therefore, in Belgium a large scale experiment was set up in co-operation with the EU Community Reference Laboratory (RIVM). In this paper the present state of the results in this area is presented. A large number of urine samples (> 50) of pregnant non-treated cows were collected and analysed by gas chromatography-mass spectrometry (GC-MS) in 4 different laboratories. Further samples (> 100) were taken, but only analysed in one laboratory. The results proved clearly that NT may indeed be detectable in the alpha form in the urine of pregnant cows, from at least 2 months, but most probably from 4-5 months before partus.

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For several years, the misuse of dexamethasone and its esters in livestock production has been clearly demonstrated. The first part of the present study deals with the elaboration of a sensitive and specific method for the determination of residues of dexamethasone in excreta at the ppb level. Sample preparation for urine and faeces, including high-performance liquid chromatography (HPLC) fractionation, was carried out. The detection was based on established methodology employing negative chemical ionization-mass spectrometry (NCI-MS) after oxidation of the dexamethasone. In comparison with previous literature, the yield of oxidized dexamethasone was substantially improved and the oxidation procedure was made more simple and robust. In the second part of the study, the relationship between the dose of dexamethasone administered and the levels of the drug in excreta was investigated using this method, as was the ratio between drug levels in urine and faeces. Treatment was carried out for 7 d with an oral dose of 50 mg d-1, the maximum levels found in urine and faeces were 980 and 744 ppb, respectively. While the elimination via faeces responded much slower at the start and the end of treatment, the final part of both excretion profiles were very similar and a level of 1 ppb was reached in both matrices 9 d after the end of treatment. Gas chromatography-mass spectrometry (GC-MS) results obtained for the urine samples were compared with those obtained with direct enzyme immunoassay.

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