MICROBIOLOGICAL DETERMINATION OF AVOPARCIN IN ANIMAL FEEDSTUFFS CONTAMINATED WITH CHLORTETRACYCLINE

The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations 1985 r equire avoparcin in compound feeds to be determined by an official mic robiological method. This method is susceptible to interference from i onophore antibiotics and chlortetracycline (CTC) which may be present in the feed owing to cross contamination during milling. The maximum c oncentration of CTC which may be tolerated by the offical method is 0. 5 mg kg(-1). An alternative microbiological assay with a tetracycline- resistant test organism which remains accurate when 40 mg kg(-1) CTC i s added, is recommended for routine laboratory assay.