Animal production intensification puts pressure on resources, leads to environmental impacts, animal welfare and biodiversity issues. Livestock products provide key components of the human diet and contribute to rural territories through ecosystem services such as nutrient and biomass recycling. Life cycle assessment (LCA) is key to assess environmental impacts in livestock systems and products. A harmonization of LCA methods is necessary to improve evaluations in these areas as LCA still lacks accuracy and robustness in addressing sustainability across livestock systems and products. Here, a participatory harmonization approach was applied to provide a framework to evaluate LCAs of current and future livestock systems. A total of 29 workshops with targeted discussions among 21 LCA experts were organised, together with two anonymous surveys to harmonise evaluation criteria. First, key research topics for improving LCAs of livestock systems were identified as follows: i) Food, feed, fuel and biomaterial competition, crop-livestock interaction and the circular economy; ii) Biodiversity; iii) Animal welfare; iv) Nutrition; v) GHG emissions. Next, general evaluation criteria were identified for livestock focussed LCA methods, considering livestock systems characteristics: Transparency and Reproducibility, Completeness, Fairness and Acceptance, Robustness and Accuracy. Evaluation criteria specific to each key topic were also identified. This participatory method was successful in narrowing down general and specific evaluation criteria through targeted discussion. Moreover, this study provided a holistic participatory framework for the evaluation of LCA methods addressing the impacts of livestock systems across a range of key topics which can be further used for other sectors
