[Tissue reactions and residues in slaughter cattle after administration of long-acting oxytetracycline formulations].

Samples from 40 slaughter cattle were investigated over 10 weeks for determining macroscopic tissue reaction following intramuscular administration of Liquamycin/LA (Pfizers) into the thigh and Terramycin/LA (Pfizers) G 333 into the neck respectively. Antibiotic residues in the lesions were assessed under ultra violet light and by microbiological means. Antibiotic residues were still detected after 7 weeks in the thigh and 5 weeks in the neck. One week old lesions in the thigh consisted mainly of a local necrotic centre, up to 120 mm in diameter, with a haemorrhagic zone and surrounded by oedema and petechia in adjacent muscle. This was gradually replaced by mainly fibrotic tissue as the weeks went by and eventually by local abscess formation still apparent 10 weeks later. Much the same pattern was seen in the neck but of milder degree and shorter duration - 6 weeks. Alarming is the fact that only in one case out of 40, a lesion could be detected in the carcass on the slaughter line, the others could have passed fit for human consumption in an abattoir. Because the manufacturer suggests a 28 day withholding period before slaughter and after administration of the product, results of this investigation raise several questions on format, completeness and contents of such directions for use and their implications for meat inspection, meat hygiene and public health.