Weight increase of the thyroid gland as a tentative screening parameter to detect the illegal use of thyreostatic compounds in slaughter cattle.

A total of 45 normal or enlarged thyroid glands of adult slaughter cattle were weighed and analyzed by thin-layer chromatography for the presence of residues of the following thyreostatic compounds: thiouracil, methylthiouracil, propylthiouracil, phenylthiouracil, and methimazole. In 21 glands, mostly from imported animals, residues of methylthiouracil or methimazole were detected. These thyroids ranged in weight from 68-245 g (mean value 118 g). Glands in which no residues were found, varied in weight between 20 and 124 g (mean value 42 g). Taking an upper limit of 60 g as normal, 4 out of 22 were false-positive' with respect to the 5 thyreostatic compounds screened for, while no false-negative cases were scored. On the basis of these results the weight increase of the thyroid gland is proposed as a simple indirect parameter in the screening for the illegal use of thyreostatic compounds in slaughter cattle.