1. Université Clermont Auvergne, INRAE, Vetagro Sup, UMR Herbivores, Saint-Genès-Champanelle, France
2. Department of Economics and Management, University of Helsinki, Helsinki, Finland
3. INRAE, University Bordeaux, CNRS, BSE, Pessac, France
4. Department of Agricultural and Resource Economics, University of Connecticut, Connecticut, USA