There have been important changes in the working conditions of farmers these last decades. The general increase in the size of farms and the reduction of the family labour had as a consequence a striving for controlled work paces ever more frequently expressed. These changes raised questions, particularly in the systems with herbivorous livestock, in view of the obligations exacted by the animals. They appear also in the context of incitations to modify the production methods and the utilization of space, which are linked to environmental challenges or to problems of product quality, with implications on the organization of work. We illustrate here a method linking the forage systems and the organization of work, whether when re-shaping a system or when implementing one. This involves the consideration of the interactions between the production process, the labour force, and the combined economic and private activities of the farmers, with the way they influence the crop year's development. We propose a model of the organization of work that describes and qualifies these interactions for limited periods or for the whole year. The aim of this model is to yield information on the forms in which work on animal farms is organized (way in which the farmers confront the tasks to be carried out and the collective labour, taking into account the constraints linked to their other economic activities and to their own desired life-style). It contributes thus to the debate on the tools for the conception of diagnoses of the farm workings that will include the organization of work; this will make it possible to discuss technical or organizational changes on the farms.