1. The Royal Veterinary College, University of London, London NW1 0TU, UK
2. Department of Clinical Studies, New Bolton Center, University of Pennsylvania, Philadelphia, PA 19348, USA
3. Faculty of Veterinary Medicine, University of Calgary, Calgary, AB T2N 1N4, Canada
4. Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 1N4, Canada