1. Bovine Health Department, Royal GD Animal Health, P.O. Box 9 7400 AA Deventer, The Netherlands
2. R&D Department, Laboratory, Royal GD Animal Health, P.O. Box 9 7400 AA Deventer, The Netherlands
3. Epidemiology and Statistics Department, Royal GD Animal Health, P.O. Box 9 7400 AA Deventer, The Netherlands