The comparison of the environmental performance of contrasting agricultural production systems using life cycle assessment (LCA) requires very specific data for each production mode, especially for direct emissions on the farm. In a case study of pig production, three contrasting production scenarios were defined: conventional good agricultural practice (GAP), organic agriculture (OA), and red label (RL). An expert panel produced methods for the estimation of emissions for key-processes of these scenarios. Clear differences were obtained for these emissions between the three scenarios. Finally, the summation of the main emissions for the entire life cycle allowed the identification of weak points for each scenario, which can be explained by the differences obtained for the emissions of the key-processes studied. © 2006 Elsevier Ltd. All rights reserved.