On line control provides real time measurement of the feed quality as it is being manufactured. Real time measurement may contribute to a better information of the quality. It allows to detect eventual disturbances of processing and to make the equipment self-running. Numerous methods are available for each step of feed processing: near infra-red spectroscopy for proximate analysis (proportioning), laser diffraction for particle size (grinding/classifying), abrasion test (pelleting). A particular attention has to be paid to sampling methodology and to the validity of the relationships between the considered quality criteria and process variables.