Abstract : Livestock farming has recently come under close scrutiny, especially in response to environmental issues. In this context, farmers may want to redesign their livestock farming systems in depth, in order to take more account of sustainable development. Systemic modelling is a relevant tool to gain holistic views of systems; I therefore challenge its potential to support such dynamics. My research question is as follows: "How to model the operation of livestock farming systems in order to support farmers in their redesign processes?". To answer this question, I carried out two complementary subprojects that consisted in: (i) analysing, through a literature review, the strengths and weaknesses of published models of livestock farming systems to support farmers in such dynamics; (ii) suggesting a method to build conceptual models of livestock farming systems operation truly structured through farmers' participation. This method was devised and tested with converted and converting dairy farmers to organic farming in the Natural Regional Park from Pilat (France, south-eastern part of Massif Central). My results show that: (i) modelling the operation of livestock farming systems in a participatory way with farmer groups is a good way to foster farmers' individual and collective thinking, which supports them in redesigning their livestock farming systems; (ii) compared with models from the literature, the models that were built with farmers through the participatory method I devised do present some qualities with regards to subsystems, time scales and disciplinary viewpoints integration. My thesis therefore offers some clues to renew the analysis frameworks used by livestock farming systems scientists, and to strengthen the links between their two following objectives: understanding the operation of livestock farming systems, and accompanying their evolution towards more sustainability. Thus, this thesis aims at fostering livestock farming systems scientists' contribution to systemic innovations in livestock farming.