1. Animal Nutrition Group, Department of Animal Sciences; Wageningen University; PO Box 338 NL-6700 AH Wageningen The Netherlands
2. Faculty of Organic Agricultural Sciences, Department of Animal Nutrition and Animal Health; University of Kassel; Nordbahnhofstraße 1a D-37213 Witzenhausen Germany
3. Department of Farm Animal Health, Faculty of Veterinary Medicine; Utrecht University; PO Box 80163 NL-3508 TD Utrecht The Netherlands