Detection of Mycobacterium avium paratuberculosis in Naturally Exposed Dairy Calves

Abstract

Johne's disease (JD) is a chronic disease of ruminants caused by Mycobacterium avium paratuberculosis (MAP). It has generally been accepted that cattle become infected as calves by ingesting MAP shed by adult cows. Due to MAP's slow-growing nature, JD has a long incubation period with clinical signs not becoming evident in infected cattle for years. However, infected cattle often shed MAP before the onset of clinical signs, albeit intermittently and at low levels. With a recent study documenting horizontal transmission of MAP from calf to calf, identifying infected cattle in the early stages of JD has become even more important. Fecal culture (FC) on Herrold's egg yolk media (HEYM) is only 50% sensitive in identifying subclinically infected adult animals. Studies using an automated liquid culture system report improved test sensitivity, capable of identifying MAP at lower levels than culture on HEYM. The purpose of this study was to determine if fecal shedding of MAP could be detected in naturally exposed dairy calves using a liquid culture system (ESP II).