1. University of Copenhagen, Grønnegårdsvej 3, 1870 Frederiksberg C, Denmark.
2. Department of Animal and Poultry Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada.
3. Prairie Swine Centre, Saskatoon, SK S7H 5N9, Canada.
4. Institute of Animal Nutrition, Department of Veterinary Medicine, Freie Universität Berlin, Königin-Luise-Strasse 49, Berlin 14195, Germany.