Effluent management causes acute problems in the Reunion Island where livestock farming is concentrated in the highlands with too little land available for spreading. A conceptual representation was developed from data collected through farm surveys, bibliographical analyses and expertise, in order to represent and better understand the management of animal wastes at the farm level. It synthesizes practical knowledge about farmer practices organised in interconnected modules representing the production, storage (discharge, emptying and transport), spreading, transformation and importing/exporting of effluents. This knowledge is described as structural and management variables and decision rules. From our findings, it appears that effluent management strongly depends upon the time left by other production activities and it is more reasoned by farmers in terms of spreading dates than in terms of quantities to be spread over. This representation aims at being sufficiently generic to account for most of the farming situations found in the Reunion Island. It can also serve as a basis to build computer models to help agricultural stakeholders evaluate and improve management strategies at the farm or, even, community levels.