The European Union (EU) relies on imports to feed livestock. In particular, protein self-sufficiency in EU for feed is not reached. Most of imported protein rich feed consist of soybean meals, which raises questions in terms of deforestation, consumer expectations for GMO-free products and security of supply. In this context, the 2014 CAP aims at improving protein self-sufficiency in EU for feed by developing production of protein-rich crops, such as legumes. Nevertheless, the development of legumes still faces economic and environmental challenges (Watson et al., 2017), such as lower annual gross margins per hectare than those of major crops and regulatory constraints which prohibit the spreading of animal manure on most legumes. The purpose of this paper is to implement an appropriate stylized framework to assess the impacts of increased protein self-sufficiency through legume development at the regional level. Both economic and environmental impacts have to be studied. Mathematical programming models offer a prospective analysis, which permits to assess agricultural practices even though they have not been introduced at large scale yet. Among mathematical programming, bio-economic models permits to assess both economic and environmental impacts. In the case of legume production, several bio-economic models have been conducted, at the field scale and at the farm scale (Schläfke et al., 2014). Such models are relevant because decision-making processes take place at the farm scale and because they help appraising farm’s sustainability. However, they fail to give indicators at higher scales, while this may be useful to policy makers. Hybrid models (Britz et al., 2012) address this issue by aggregating results from the farm to the region. These models usually take into account the diversity of farms but they badly represent the heterogeneity of soil and climate conditions. In the case of legume production, conditions such as soil pH and water deficit have to be taken into account because they limit the possibilities of implanting legumes. Besides, one of the levers to increase the production of legumes has been very little studied: the complementarity of farms. On the one hand, livestock farms could export animal manure to crop farms, which are deficient in nitrogen for crop fertilization. On the other hand, crop farms could produce legumes and trade it in order to feed animals of livestock farms. Our hypothesis is that increasing protein self-sufficiency through legume exchanges between farms can have positive economic and environmental impacts. MATERIAL AND METHODS The bio-economic model SYNERGY proposed here is in direct line with these considerations. First, it is a hybrid model implemented at farm scale and then, aggregated at the regional level. Second, it takes into account various types of farm (crop farm, dairy farm, hog farm) as well as the heterogeneity of soil and climatic conditions. Third, the complementarity of farms is highlighted by accounting for exchanges of legumes and animal manure between farms. SYNERGY optimizes the sum of each farm’s expected income at the regional level. It is composed of five modules: four modules describe farm activities (i.e., the cropping module, the fertilization module, the livestock module and the feeding module). Thanks to farm activities, farmers produce commodities (i) to self-supply needs for their management systems (e.g., a livestock farmer can use crops grown on its farm to feed his animals) and, (ii) to sell them on markets. Depending on the commodity, commodities can be exchanged on either local markets (i.e., to other farms of the region), on worldwide market or on both markets. The fifth module permits to assess environmental impacts through nitrogen-related indicators: SyNE (System Nitrogen Efficiency) and SyNB (System N Balance) based on (Godinot et al., 2014) have been integrated. SYNERGY is implemented on a stylized area inspired from a small region of western France where livestock farms are dominant. Three scenarios are simulated: the baseline scenario (B), which should reproduce the observed data; the scenario (SC1) where local exchanges between farms are made possible; the scenario (SC2) where, in addition to these local exchanges, a GMO-free certification is implemented for animal commodities for produced from legume-based rations instead of soybean-based rations. SYNERGY generates three types of outputs: (i) an assessment of protein self-sufficiency in animal feed, (ii) an economic assessment by calculating incomes and, (iii) an environmental assessment by calculating the nitrogen-related indicators SyNE and SyNB. All these assessments are done at the farm scale, and at the regional level through a scaling process. RESULTS AND DISCUSSION SYNERGY model currently incorporates limited and highly constrained technical alternatives (i.e., soybean-based ration vs legume-based). Thus, the first results can only be interpreted in relation to the trends they present. When local exchanges between farms are possible (scenario SC1), protein self-sufficiency rises at the regional level, as do incomes. However, this greater self-sufficiency is not associated with an increase in the legumes area, but only with local exchanges of cereals. Thus, protein self-sufficiency is not only linked with protein rich materials but must be seen in a more comprehensive way by taking into account all sources of proteins. When a GMO-free certification is added(scenario SC2), the legumes area increases significantly and exchanges of legumes between crop farm and livestock farms happen. Protein self-sufficiency is improved thanks to a substitution of soybean-based rations for legume-based rations. However, the self-sufficiency is not strengthened compared to scenario SC2. One of the reason is that the legume-based ration for pig is less effective than the soybean-based ration. Concerning the environmental assessment, in both SC1 and SC2 scenarios, SyNE indicator decreases and SyNB indicator increases in all types of farms. Thus, farms become less efficient in N and N losses become higher than in the baseline scenario (B). CONCLUSION The purpose of this paper was to implement an appropriate stylized framework to assess the impacts of increased protein self-sufficiency through legume development at the regional level. The results show that protein self-sufficiency can initially be strengthened at the regional level, thanks to local exchanges of cereals. It can also be enhanced to the same extent by the development and exchanges of legumes, when a market for differentiated feeds such as GMO-free animal products, exists. Thus, SYNERGY model highlights that the complementarity between livestock farms and crop farms is a relevant lever for improving regional protein self-sufficiency.