Technical groups of dairy farmers have developed autonomous and economical farming systems using bottom-up innovation processes. Nurse cow reaning, a new ay to rear young calves, was designed within such groups. The aim of our research was to analyse how organic dairy farms implement these rearing systems. We conducted qualitative interviews with farmers to explore relations between rearing practices, farmers' objectives and farm characteristics. Our results indicate that this innovation is based on a few elements : (1) it was designed in a systemic manner, (2) it fits with farmers' production and economic goals and (3) it can be adapted to each farm.