Detection of a high prevalence of paratuberculosis in a previously test‐negative conventional dairy herd in the Netherlands

Abstract Johne's disease, or paratuberculosis, in cattle, caused by Mycobacterium avium subspecies paratuberculosis (MAP), can cause substantial economic losses on dairy farms. This case study describes the finding of a MAP prevalence of 8% in a Dutch dairy herd with a 10‐year history of biennial enzyme‐linked immunosorbent assay‐negative testing in individual milk samples of lactating cows. This case illustrates the strengths and limitations of the different laboratory tests and testing schemes for MAP screening in dairy herds. A cluster of MAP‐shedding cattle on this farm was related to a birth cohort, which suggests a common source of infection early in life. Our observations stress the importance of preventive management to reduce the potential and hidden spread of MAP in test‐negative herds.