In Western countries during the post-World War II decades, endemic viral diseases were increasingly important to health. Such diseases have attracted limited historical attention. Due to changing methods of livestock production, they were particularly prevalent on the farm. This article uses a case study of the cattle disease, bovine viral diarrhoea (BVD), to demonstrate their historical significance. Spanning North America, the UK and Australia, it reveals the complex nature of BVD, and how and why its clinical, aetiological, epidemiological and host species identities evolved over time. This analysis sheds new light on how endemic viral diseases of livestock were experienced, understood and distributed in this period, and the influence exerted by changing agricultural practices, concerns about biological warfare and the development of virology as applied to veterinary medicine.