Discussion

Aims: To assess the extent of obsolete data retained in the National Equine Database and to evaluate the extent of spatial separation between horse and owner location and apply this information to developing a credible national distribution of horses in Britain. Methods: The amount of obsolete data retained in NED was estimated using a survey of 11,000 NED-registered horse owners. A national distribution of horses was developed based on adjustments for overall population size using previously calculated missing data, owner-horse spatial separation and land usage. Results: Of 1382 questionnaires completed, 380 passports were obsolete (27.5%; 25.2 - 29.9%), with 162 (11.7%; 10.0 - 13.4%) of those being passports retained for deceased horses and 218 (15.8%; 13.9 - 17.7%) being passports with incorrect ownership details. Fifty-three percent (49.9 - 56.1%) of owners kept their horses at their home address, and 92% (90.3 - 93.7%) of horses resided within 10 km of their owners. These data, used in conjunction with previously estimated missing data, subsequently facilitated development of a national distribution of horses in Britain suitable for risk modelling of equine infectious diseases. Conclusions and practical relevance: Although missing and obsolete data act to cancel each other out to some extent, they would affect NED's efficiency to rapidly locate horses and owners in the event of a major disease outbreak. Taking these data into account, the horse population was calculated at 1.1016 million, within 95% confidence limits of 1.0776 million - 1.1256 million horses. Appropriate adjustment for population size, owner-horse spatial separation and land usage would facilitate meaningful use of the national horse population derived from NED for equine disease surveillance purposes. Acknowledgements: The authors would like to acknowledge the generous support received from the Horserace Betting Levy Board. James Wood is supported by the Alborada Trust and the RAPIDD program of the Science and Technology Directorate, US Department of Homeland Security.