1. Department of Animal Science and Animal Health, Division of Animal Nutrition, Royal Veterinary and Agricultural University, DK-1870 Frederiksberg, Denmark
2. Department of Medical Physiology, University of Copenhagen, DK-2200 Copenhagen, Denmark
3. Unité Mixte de Recherches sur le Veau et le Porc, INRA, 35042 Rennes Cedex, France