1. Department of Animal Health and Welfare; Danish Institute of Agricultural Sciences; Research Centre Foulum; PO Box 50 DK-8830 Tjele Denmark
2. Department of Cattle Nutrition; Danish Cattle Federation; Udkaersvej 15, Skejby DK-8200 Aarhus N Denmark
3. Department of Animal Science and Animal Health; Royal Veterinary and Agricultural University; Grønnegårdsvej 8 DK-1870 Frederiksberg C Denmark