This article advances historical understandings of health, veterinary medicine and livestock agriculture by examining how, in mid-twentieth-century Britain, the diseases of livestock were made collectively knowable. During this period, the state extended its gaze beyond a few, highly impactful notifiable diseases to a host of other threats to livestock health. The prime mechanism through which this was achieved was the disease survey. Paralleling wider developments in survey practices, it grew from small interwar beginnings into a hugely expensive, wide-ranging state veterinary project that created a new conception of the nation’s livestock as a geographical aggregation of animals in varying states of health. This article traces the disease survey’s entanglements with dairy cows, farming practices, veterinary professional politics and government agendas. It shows that far from a neutral reflection of reality, surveys both represented and perpetuated specific versions of dairy cow health, varieties of farming practice and visions of the veterinary professional role. At first, their findings proved influential, but over time they found it harder to discipline their increasingly complex human, animal and disease subjects, resulting in unconvincing representations of reality that led ultimately to their marginalization.