Combining life cycle analysis (LCA) and simulation modelling (SM) has been used to assess and improve a collective manure management plan set up in Brittany (north-western France) by a group of farmers to comply with current Nitrogen reduction regulations in agriculture. The plan studied aimed at organizing the spreading of slurry surpluses produced by 11 pig farms (representing 57.6 tons N/year) on crop land loaned by 22 crop farms located approximately 44 km away. LCA was used according to its normalized methodology to statically assess the potential environmental impacts based on 4 criteria: eutrophication, climate change, acidification and use of non-renewable energy. COMET, the dynamic systems model used in this study, has been implemented with the Vensim® software by coupling: logistics models, to simulate the transportation and spreading of manure, both at the individual (within farms) and collective (transfer plan) levels; biophysical models, mainly empirical, to simulate ammonia (NH3) and methane (CH4) emissions as the main criteria of the environmental evaluation with COMET. The approach encompassed four steps that alternated between the LCA and SM methodologies: (i) LCA was initially performed to assess the environmental impacts of two disposal scenarios, i.e. slurry biological treatment or transfer for application to remote crop farms. The analysis concluded the transfer scenario had the least environmental impact as, if properly implemented, it may save on the use of chemical fertilizers. (ii) SM using the COMET model simulated the logistics and agricultural feasibility of the transfer scenario to verify to what extent the collective management plan can be fully completed in due time on appropriate cropping systems. (iii) A second iteration of LCA was made to assess the environmental impacts of simulated variants of the transfer scenario, this time using simulation outputs instead of reference database information. These analyses showed important differ