Microbiological determination of avoparcin in animal feedstuffs contaminated with chlortetracycline

Abstract

The Medicines (Animal Feeding Stuffs)(Enforcement) Regulations 1985 require avoparcin in compound feeds to be determined by an official microbiological method. This method is susceptible to interference from ionophore antibiotics and chlortetracycline (CTC) which may be present in the feed owing to cross-contamination during milling. The maximum concentration of CTC which may be tolerated by the official 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 is added, is recommended for routine laboratory assay.