David Reddick, Head of Animal Health at Moredun Scientific and Willie Donachie, visiting professor at the University of Glasgow and Heriot Watt University explain how validated experimental models of livestock infectious disease are important tools for the generation of efficacy data for candidate veterinary medicinal products. The article outlines key elements in the development and successful application of experimental models, including the strain of the pathogen used in the experimental challenge, and volume and titre of challenge material.