This paper presents a simulation project of winter forage harvests management on pyrenean farms.The coupling of a decision process madel with a production process madel, bath derived from previous studies in this area, allows the building of a simulation tool in arder to predict the results of alternative managements. ln this work we intend to consider changes in farm structure (fields characteristics and farm equipment) and in management practices. The main objective is to give an account of the role of the heterogeneity of the meadows fields as a constraint for organizing forage systems. We discuss the choices made during the building of this madel and of a prototype computer-simulation tool.