1. Animal Sciences Group of Wageningen University and Research Centre, Animal Production Division, P.O. Box 65, 8200 AB Lelystad, The Netherlands
2. Institute of Animal Husbandry and Breeding (470c), Section Farm Animal Ethology and Small Animal Sciences, Garbenstr. 17, D-70599 Stuttgart, Germany
3. ADAS UK Ltd., Gleadthorpe, Meden Vale, Mansfield, Nottinghamshire, NG20 9PF, UK
4. INRA, Unité de Recherches Avicoles, Centre de Tours-Nouzilly, 37380 Nouzilly, France
5. Danish Institute of Agricultural Sciences, Dept. of Genetics and Biotechnology, Tjele, Denmark.
6. Faculty of Veterinary Medicine, University of Zaragoza, Miguel Servet 177 (50013) Zaragoza, Spain
7. University of Bristol, School of Clinical Veterinary Science, Langford House, Langford, Bristol, BS40 5DU, UK
8. Swedish University of Agricultural Sciences, Dep. of Animal Nutrition and Management, Avian Division, Kungsängen Research Centre, 753 23 Uppsala, Sweden