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 medicated. These were subjected to analysis for the presence of antibiotics. Of the 247 medicated feeds 87 (35.2) contained undeclared antimicrobials 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) contained concentrations which could be quantified by HPLC. The most frequently identified contaminating antimicrobials were chlortetracycline (CTC) (15.2), sulphonamides (6.9), penicillin (3.4) and ionophores (3.4). Four samples (ionophores#x2014;3, sulphadimidine#x2014;1) contained therapeutic concentrations and one sample a supra#x2010;therapeutic concentration (monensin). The remainder were sub#x2010;therapeutic. All the contaminating concentrations of sulphadimidine detected were sufficient to cause violative tissue residues if fed to animals immediately prior to slaughter.
展开▼
