1. Department of Animal and Food Sciences, University of Delaware, Newark, DE 19717, USA
2. Statistics Program, Department of Food and Resource Economics, University of Delaware, Newark, DE 19717, USA
3. Department of Poultry Science, University of Georgia, Athens, GA 30602, USA
4. Station de Recherches Avicoles, Institut National de la Recherche Agronomique, Nouzilly 37 380, France
5. Department of Animal and Avian Sciences, University of Maryland, College Park, MD 20742, USA