1. Graduate Program in Agricultural Economics, Colorado State University, Fort Collins , CO 80523, USA
2. Agricultural and Resource Economics Department, Colorado State University, Fort Collins , CO 80523, USA
3. Department of Economics, Administration and Sociology, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba , 13403, Brazil
4. Laboratory of Epidemiology and Biostatistics, School of Veterinary Medicine and Animal Science, University of São Paulo, São Paulo , 05508060, Brazil