To improve sustainability, farmers may want toredesign their livestock farming systems in depth. Systemicmodelling has proved an efficient tool to study complexissues regarding farming systems, but it remains inefficientto support farmers in their system redesign processes. Thispaper describes and discusses a novel method to modellivestock farming systems with groups of farmers to helpthem redesign their own systems. Modelling livestock farmingsystems at the farm scale with farmer groups is anoriginal approach in livestock farming system modelling.Following a constructivist approach, our method involvesworking with farmers already involved in redesign processesand building causal maps according to their own representations,without using models previously created byscientists. Applying the method, we built two causal mapsof livestock farming system operation, each one built with agroup of five farmers including both those converting andconverted to organic farming. Converting to organic farmingwas considered as one example of a redesign process.On the basis of a subjective assessment by both the participatingfarmers and researchers, and an analysis of mapstructures, we assessed the method’s strengths and weaknesses.We considered that one of its main advantages lay inits collective dimension: sharing, comparing and questioninginterested the participating farmers greatly; however, itrequires good facilitation skills and suitable group composition.Furthermore, the formalising process identified, forexample, vicious circles in system operation, which madethe farmers think about solutions for breaking them. Finally,analysis of map structures identified similarities and differencesbetween the two groups that were discussed with bothof them during a final workshop; this activity continuedfarmers’ self-reflection about their systems, which may helplead to innovative and more sustainable livestock farmingsystems.