Occurrence of faecal shedding of Mycobacterium avium subs. paratuberculosis by calves

Paratuberculosis or Johne´s disease is a chronic granulomatous enteric disease afflicting cattle, sheep, goats and other ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Calves are infected mainly via an oral route, especially from manure and environment contamination by infected adult cattle. It is generally assumed that calves rarely shed MAP bacteria and that calf-to-calf transmission is of minor importance. The aim of the study was to evaluate occurrence of faecal excretion of MAP by calves born to MAP-positive and MAP-negative dams in a low MAP prevalence herd. The study involved 66 dam-calf pairs. Samples of faeces were collected: for each cow once about 2–3 weeks to parturition, and for each calf 3 times at 2–5, 180–185 and 360–365 days of age. All samples were studied for the presence of MAP by culture or by PCR of IS900 insertion sequence MAP DNA. Faecal samples of the dams demonstrated 15/66 dams with at least one positive result. Analysis of MAP shedding prevalence in the faeces of calves originating from MAP-positive and MAP-negative dams shows that in 15 MAP-positive dams- 10 out of 15 calves (66.66%) at the age of 180–185 days and at the aged of 360–365 days 11 out of 15 calves (73.33%) were MAP-positive in faecal samples. In the case of MAP-negative dams: 7 out of 51 calves (13.72%) at the age of 180–185 days, and 8 out of 51 calves (15.68%) at the age of 360–365 days were MAP-positive. MAP-infection cases in calves coming from infected and healthy dams prove the occurrence of calf-to-calf transmission and that contact with infected calves increases the risk of MAP spreading among healthy calves.