The detection of the illegal use of clenbuterol (CBL) as a growth promoter has relied on detecting residual concentrations of the drug in body fluids or tissues. Analysis of retinal extracts has recently been shown to considerably extend the detection period following withdrawal. The withdrawal periods required to eliminate residues from the liver and retina were investigated by medicating 20 cattle with CBL for 30 days; 6 control animals remained unmedicated. Residual concentrations were monitored throughout this period and for the subsequent 140 days. Concurrent changes in muscle areas and backfat thicknesses were recorded by ultrasound. CBL was detectable in liver up to the 56th day of withdrawal (0.35 ng/g, SD = 0.5), but retinal concentrations remained well above detectable concentrations throughout the withdrawal period (22.5 ng/g, SD = 6.5). There were small gains (3-4%) in the muscle areas of treated cattle during medication as compared to controls (p > 0.05). These comparative gains remained during withdrawal. Backfat thicknesses in treated animals were 40% lower than in controls at the end of medication (p < 0.01). However, by 70 days after withdrawal this difference had disappeared (p > 0.05) owing to accelerated fat deposition in the treated group. The retina has been shown to be a highly effective target matrix for detecting CBL administration after long withdrawal periods.

Improvements have been made to a previously described multi-mycotoxin method that involved a membrane cleanup step. Using 2-dimensional thin layer chromatography and appropriate solvent systems, aflatoxin B1 can be detected in mixed feedstuffs and various ingredients at levels ranging from 0.1 to 0.3 μg/kg. Corresponding detection limits for ochratoxin A and sterigmatocystin are 5 to 20 μg/kg and for T-2 toxin and zearalenone 20 to 200 μg/kg.

A multimycotoxin thin layer chromatographic screening method is described which is applicable to most animal feedstuffs. Interference from nonspecific lipid, pigment, and other components of simple and mixed feeds is reduced to a minimum by using a membrane cleanup step. Aflatoxins B1, B2, G1, and G2, citrinin, diacetoxyscirpenol, ochratoxin A, patulin, penitrem A, sterigmatocystin, T-2 toxin, and zearalenone may be reliably detected. The sensitivity of the method is generally low for mixed feeds but even so aftatoxin B4 can be detected at a level of 3 ppb and ochratoxin A at 80 ppb. While the basic method is less sensitive for sterigmatocystin (330 ppb), patulin (600 ppb), zearalcnone (1000 ppb), and the trichothecenes (1000–4000 ppb), it may be adapted so as to reduce the above detection limits when the presence of these toxins is suspected. Lower levels may be detected in extracts of simple feeds.

A quantitative procedure widely used in European Economic Community (EEC) countries has been successfully scaled down to produce a rapid method for determination of af latoxin B1 (and other anatoxins) in animal feeds. Without modification, the method may be used for simultaneous ochratoxin A determination in simple feeds, but a slightly different extraction procedure is required for compound feeds. Validity of the method has been demonstrated by comparison with the full EEC procedure for aflatoxin B1 and the Nesheim method for ochratoxin A. Analyses may be completed within 2 h and there is a considerable savings in materials over the 2 reference methods. The procedure is also less hazardous because volumes of toxic extract are small, and the operator is exposed to minimum solvent vapor.

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