This document describes a method for determination of the massic activity (Bq/kg) of 131I, 134Cs and 137Cs in animal feed in monitoring laboratories. General guidance on the preparation of feed samples and the measurement of the three radionuclides 131I, 134Cs and 137Cs by high resolution gamma-ray spectrometry is provided. The current document aims to be complementary to existing standards. More information on sample preparation, moisture content determination and gamma-ray spectrometry can be found in specific standards referred to in this document. For example, generic advice on the equipment selection, detectors and quality assurance for gamma-ray spectrometry can be found in ISO 20042. The method was fully statistically tested and evaluated in a collaborative trial comprising five animal feeding stuff samples for the radionuclides 131I, 134Cs and 137Cs. Details on the successfully tested working range for each of the examined radionuclides are described in Annex C.