Tissue distribution and residues of clenbuterol, salbutamol, and terbutaline in tissues of treated broiler chickens.

To examine the tissue distribution and residues after withdrawal of various beta-agonists (i.e., clenbuterol, salbutamol, and terbutaline) 160 1-d-old broiler chickens were assigned to four groups. During treatment (16 to 35 d), the birds were fed a control diet or a diet containing 1 ppm of clenbuterol, 10 ppm of salbutamol, or 10 ppm of terbutaline. After d 35 all groups received the control diet. Five birds of each group were then slaughtered and tissues were collected on d 0, 1, 2, 3, 7, 14, and 43 following withdrawal of beta-agonists from the feed. Extraction of beta-agonists from the tissues was carried out by a new method using hetero-bifunctional solid phase extraction. The amount of beta-agonists in the extracts was measured by an enzyme immunoassay (EIA). The highest concentrations of beta-agonists were found in feathers: 224 ng of clenbuterol/g, 1,140 ng of salbutamol/g, and 1,159 ng of terbutaline/g. Clenbuterol accumulated above plasma levels in all tissues that were investigated (liver, kidney, stomach, muscle, fat, feather, eye). Salbutamol was most concentrated in feather, eye, liver, and kidney; terbutaline accumulated only in feather, liver, and kidney. Overall, clenbuterol showed the highest accumulation in the tissues analyzed. A withdrawal period of greater than 2 wk was required for residues in edible tissues to decline below detectable levels.