Clinical and Subclinical Diseases Predisposing to Johne's Disease in Dairy Cattle

Abstract

Paratuberculosis or Johne's disease (JD) is a chronic and progressive intestinal disease in ruminants caused by Mycobacterium avium subsp paratuberculosis (MAP). The usual route of infection is fecal-oral, with young cattle becoming infected by exposure to infected adults or their environment. The factors that trigger MAP fecal shedding or JD clinical disease are not understood and little information is provided about it in the literature; why do some cows that already shed the organism in the feces suddenly break into the clinical phase, whereas other shedding herdmates continue in the subclinical phase? The objectives of this study were to identify associations between clinical or subclinical diseases and risk for subsequent occurrence of clinical Johne's disease (JD) and onset of fecal shedding after 305 days in milk (DIM).