CONTAMINATION OF ANIMAL FEEDING STUFFS WITH UNDECLARED ANTIMICROBIAL ADDITIVES

A study was carried out on 397 feedingstuffs and 11 premixes on which 161 (39.5%) were declared free of medication and 247 (60.5%) were medi cated. These were subjected to analysis for the presence of antibiotic s. Of the 247 medicated feeds 87 (35.2%) contained undeclared antimicr obials of which 59 (23.9%) were at a concentration sufficient to allow quantification by HPLC. Of the 161 unmedicated feeds 71 (44.1%) were shown to contain detectable antimicrobials of which 42 (26.1%) contain ed concentrations which could be quantified by HPLC. The most frequent ly identified contaminating antimicrobials were chlortetracycline (CTC ) (15.2%), sulphonamides (6.9%), penicillin (3.4%) and ionophores (3.4 %). Four samples (ionophores-3, sulphadimidine-1) contained therapeuti c concentrations and one sample a supra-therapeutic concentration (mon ensin). The remainder were sub-therapeutic. all the contaminating conc entrations of sulphadimidine detected were sufficient to cause violati ve tissue residues if fed to animals immediately prior to slaughter.