1. DSM Food Specialties, R&D−FTD, P.O. Box 1, 2600 MA Delft, The Netherlands, Animal Nutrition Group, Wageningen University & Research Center, P.O. Box 338, 6700 AH Wageningen, The Netherlands, and Division Nutrition and Food, Animal Sciences Group, Wageningen University & Research Center, P.O. Box 65. 8200 AB, Lelystad, The Netherlands