RESIDUES FROM LONG-ACTING ANTIMICROBIAL PREPARATIONS IN INJECTION SITES IN CATTLE

Objective To investigate tissue residues of two long-acting oxytetracy cline (OTC) preparations in cattle. Design A randomised drug residue t rial. Animals Two hundred and forty beef cattle in 24 groups of ten. P rocedure Two blind-coded 200 mg/mL OTC preparations were used in five treatment regimens of various combinations of injection sites (from on e to five) and administrations (one or two). Five cattle from each gro up were slaughtered at 21, 30 and 60 days after injection and the inje ction site, urine, kidney and diaphragm muscle analysed for residues. Results The OTC concentration exceeded the maximum residue limit in ki dney in animals slaughtered 21 days after treatment, which is the pres cribed withholding period. Concentration at the injection site was muc h greater than the maximum residue limit 30 days post-treatment, but n ot 45 days post-treatment. The residue was smaller when OTC had been i njected in multiple sites. There was no difference between the two OTC preparations. Conclusion A review of the maximum injection volume, si te of injection and the withholding period is needed for long-acting O TC formulations.