This chapter explores how the debate on veterinary medicine may be taken beyond the study of the political and economic effects of stock control and into the area of the historical sociology of knowledge. It focuses on the interaction between vets and the Maasai of Kenya and Tanzania during and after the colonial period. The chapter suggests that modern epidemiological events should be interpreted in the light of conflicts between state policy and pastoralist strategy. It deals with the practical outcome of disputes over knowledge and authority, for different systems of veterinary knowledge informed different and competing strategies of stock management in postcolonial as well as colonial times. The chapter outlines briefly how Maasai stock owners have attempted to deal with disease and how this has conflicted with state policy.