1. Independent Scientist, P.O. Box 323, 6700 AH Wageningen, The Netherlands
2. Department
of Agroecology and Environment, Faculty of Agricultural Science, Aarhus University, Blichers Allé 20, P.O. Box 50, 8830 Tjele, Denmark
3. Department
of Animal Sciences, Faculty of Agricultural Science, Aarhus University, Blichers
Allé 20, P.O. Box 50, 8830 Tjele, Denmark