This article traces and contextualizes the development of veterinary policy in Kenya from 1900 to 1940, with particular reference to three diseases: East Coast Fever, bovine pleuro-pneumonia and rinderpest. Disease affected almost every aspect of society and economy in Kenya, but the threat that it posed was constructed and confronted differently by the various constituencies – official, settler and African – that made up the divided pastoral economy. Policy emerged and changed from containment to eradication as the result of continuous argument, in which the Colonial Office played a key role, about both the nature of disease and the most effective way of combating it.