Henk Bovenhuis1, Sabine van Engelen1, Marleen H P W Visker2. 1. Wageningen University and Research, Animal Breeding and Genomics, PO Box 338, 6700 AH, Wageningen, the Netherlands. 2. Wageningen University and Research, Animal Breeding and Genomics, PO Box 338, 6700 AH, Wageningen, the Netherlands. Electronic address: marleen.visker@wur.nl.