Ct. Elliott et al., OBSERVATIONS ON THE EFFECTS OF LONG-TERM WITHDRAWAL ON CARCASS COMPOSITION AND RESIDUE CONCENTRATIONS IN CLENBUTEROL-MEDICATED CATTLE, Veterinary research communications, 17(6), 1993, pp. 459-468
The detection of the illegal use of clenbuterol (CBL) as a growth prom
oter has relied on detecting residual concentrations of the drug in bo
dy fluids or tissues. Analysis of retinal extracts has recently been s
hown 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 d
ays; 6 control animals remained unmedicated. Residual concentrations w
ere monitored throughout this period and for the subsequent 140 days.
Concurrent changes in muscle areas and backfat thicknesses were record
ed by ultrasound. CBL was detectable in liver up to the 56th day of wi
thdrawal (0.35 ng/g, SD = 0.5), but retinal concentrations remained we
ll above detectable concentrations throughout the withdrawal period (2
2.5 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 thickness
es in treated animals were 40% lower than in controls at the end of me
dication (p<0.01). However, by 70 day; after withdrawal this differenc
e had disappeared (p>0.05) owing to accelerated fat deposition in the
treated group. The retina has been shown to be a highly effective targ
et matrix for detecting CBL administration after long withdrawal perio
ds.