This paper explores the wartime creation of veterinary expertise in cattle breeding, and its contribution to the transition between two very different types of agriculture. During the interwar period, falling prices and steep competition from imports caused farmers to adopt a ‘low input, low output’ approach. To cut costs, they usually butchered, marketed or doctored diseased cows in preference to seeking veterinary aid. World War II forced a greater dependence on domestic food production, and inspired wide-ranging state-directed attempts to increase (...) agricultural output. However, the weak connection between veterinary services and livestock productivity meant that the drive for greater milk yields did not automatically translate into a demand for improved veterinary health care. Rather veterinary expertise had to be actively created and made relevant to the new context. Leaders of the profession secured this goal through establishing a government-backed ‘scheme for the control of certain diseases of dairy cows’. Drawing on pre-existing but rarely applied reproductive technologies, the scheme provided the opportunities and education necessary for more extensive veterinary interventions in cattle breeding. I show how its operation transformed understandings of fertility, raised veterinarians to the status of experts, won them the patronage of farmers and the state, and facilitated the shift to a productivity-oriented agriculture. (shrink)