1. Teagasc, Animal & Bioscience Research Department, Moorepark, Fermoy, Co. Cork, Ireland
2. Department of Agriculture, Food and the Marine, Backweston Campus, Celbridge W23 X3PH, Co. Kildare, Ireland
3. Centre for Veterinary Epidemiology and Risk Analysis (CVERA), UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, D04 W6F6, Ireland
4. Teagasc, Animal & Bioscience Research Department, AGRIC, Grange, Dunsany, Co. Meath, Ireland
5. Department of Agriculture, Food and the Marine Laboratories, Athlone Regional Veterinary Laboratory, Coosan, Athlone N37 N471, Ireland