47. Multi-objective formulation is an efficient methodology to reduce environmental impacts of pig feeds F. Garcia-Launay 1,* , A. Wilfart 2 , L. Dusart 3 C. Nzally 1 , , D. Gaudré 4 , Y. Dronne 5 , S. Espagnol 4 1 PEGASE, INRA, Agrocampus-Ouest, 35590 Saint-Gilles, France 2 SAS, INRA, Agrocampus Ouest, 35042 Rennes, France 3 ITAVI, 37380 Nouzilly, France 4 IFIP, Institut du porc, BP 35104, 35651 Le Rheu, France 5 FeedSim Avenir, 35042 Rennes, France * Corresponding author: Email: Florence.garcia-launay@rennes.inra.fr ABSTRACT The production of pig feeds has a major contribution to climate change, energy use and land occupation impacts of the animal product. Nonetheless, the traditional least-cost (LC) feed formulation methods minimize the cost of the feed mix, without consideration of its environmental impacts. The objective of this study was to estimate the potential mitigation of environmental impacts calculated by Life Cycle Assessment through a multi-objective formulation of pig feeds, in the French context. The linear programming problem built searches the best feed formula under nutritional constraints with a multi-objective function including an economic price index (price of the feed mix relative to LC formulation) and an environmental impacts index (environmental impacts relative to LC formulation). A weighting coefficient between price and environment () ranging from 0 to 1 was included. Growing and finishing feeds were formulated with two scenarios of feed ingredients availability (current limited LIM, increased NLIM) and 4 scenarios of feed ingredient prices. When increasing  from 0 to 0.5, the environmental indexes of the growing and finishing feeds dropped down to -10% in LIM and down to -17 to -20% in NLIM scenario, respectively. Concomitantly, the average feed price increased by 1.5% in LIM and 1.7% in NLIM. For  higher than 0.5, the environmental index was almost no further reduced. At =0.5, all the impacts considered were reduced relatively to LIM-LC, excepted for land occupation in NLIM. The low-impact feeds incorporated higher proportions of pea and wheat middlings and lower proportions of meals (rapeseed and sunflower) than LC formulated feeds. The multi-objective formulation of pig feeds is an efficient methodology to find low-impact feeds according to a given economic scenario. Improving the availability of some feed ingredients (pea, co-products of wheat…) at the territory level would allow (at same feed’s nutritional composition) further reduction of pig feeds impacts relatively to the current French context. Multi-objective formulation can provide a decision support tool to the feed industry to produce low-impact feeds for the pig production chain. Keywords: optimization, feed formulas, linear programming, pig feeds. 1. Introduction Pig production systems (PPS) are facing societal, environmental and economic challenges all around the world. Animal production is expected to increase in the following years to feed the raising human demand for animal products (FAO, 2011). PPS should also reduce their environmental burden. They are associated various environmental impacts like climate change, land use, and eutrophication particularly in territories with high concentrations of livestock (North West France, Netherlands…). The rising of the feed ingredients prices (cereals and meals from oilseeds and protein crops) and the volatility of the animal products prices also reduce the stability and the average level of the gross margin of pig producers (EC, 2013). In farrow-to-finish PPS, feeds account for 60% to 70% of the feeding cost and the production of feeds has a major contribution to climate change (55%-75%), energy use (70%-90%) and land occupation (85%-100%) impacts of the animal product (Basset-Mens and van der Werf, 2005; Dourmad et al., 2014). Both feeds’ cost and environmental impacts are highly determined by their composition in feed ingredients. Some of them, like soybean meal, account for more than 10% of the feed composition and are characterized by relatively high price and impacts (Wilfart et al., 2016). Some other feed ingredients are incorporated into small amounts into feeds but have high environmental impacts per kilogram, e.g. feed-use amino acids and monocalcium phosphate (Garcia-Launay et al., 2014). Therefore, there is possibly a great potential to reduce the environmental impacts of animal products through the formulation of low-impact feeds (Nguyen et al., 2012). Nonetheless, the traditional least-cost (LC) feed formulation method minimizes the cost of the feed mix, without consideration of its environmental impacts. LC formulation incorporates the feed ingredients to meet nutritional requirements according to production objectives, while minimizing the cost of the feed mix, using a linear programming model which calculates the feed cost as the objective function. However, the maximal technical performance does not necessarily correspond to the