1 Animal Production Systems Group, Wageningen University & Research, P.O. Box 338, 6700 AH Wageningen, the Netherlands. Electronic address: evelien.deolde@wur.nl.
2 Marketing for Food and Agricultural Products, Faculty of Agricultural Sciences, University of Goettingen, Platz der Goettinger Sieben 5, 37073 Göttingen, Lower-Saxony, Germany.