Johne's disease in dairy herds 1. Understanding the disease

Background: Johne's disease (JD) is regarded as an incurable, chronic, debilitating disease of cattle that causes scour, weight loss and death. However, these clinical signs are rarely seen and tend to be sporadic with a low prevalence, even in affected herds. Increasing interest in the management of JD, particularly in dairy herds, has been brought about by recognition that it is associated with many other conditions such as mastitis, lameness, poor productivity and decreased production efficiency. Affected herds typically have high forced culling rates and inefficient productivity. Modern dairy farming – particularly the increase in herd size and the husbandry procedures around parturition and neonatal calf care – has led to an increased risk of the spread of JD within herds and, thus, rising prevalence, albeit in the subclinical form. However, these trends can be reversed with benefits for all concerned. Aim of the article: This is the first article in a two‐part series and aims to give guidance on how JD can be controlled, managed and avoided in modern dairy herds, as well as how to comply with the guidance and requirements of the National Johne's Management Plan. The second article, to be published in a subsequent issue of In Practice, discusses how to achieve effective control using the plan.