This paper analyses the importance of boundaries in the control of animal disease. On the one hand, establishing geographical and disciplinary boundaries is seen to be vital to the control of disease. In practice, however, boundaries are unstable, disrupted and frequently transgressed. Disease and its diagnosis vary in space, while disciplinary boundaries between epidemiology, laboratory and clinical practices can collapse from the non‐coherence of disease. Drawing on the concepts of ‘disciplinary borderlands’ and fluid space, the paper analyses how uncertainty over disease diagnosis establishes a veterinary borderland in which disciplines are merged and combined and difficult to tell apart. From archival research and interviews of key informants, the paper describes the history of the control of bovine tuberculosis (bTB) in New Zealand. Focusing on disputes around the diagnosis of bTB in the West Coast region, the paper shows how the problem of non‐specificity (locally referred to as ‘heiferlumps’) undermined attempts to impose a universal version of disease and control policy. In this new veterinary borderland, attempts to manage the non‐coherence of disease shifted from denial to viewing disease as a moral problem in which farmers’ own knowledges were central to the definition and management of disease. In doing so, boundaries between traditional disease disciplines were broken down, and new hybrid veterinary practices established to create geographically variable disease control rules and procedures. In conclusion, the paper considers the wider consequences for the management of animal disease arising from greater farmer involvement in animal disease management.