Incidence of Paratuberculosis after Vaccination againstM. paratuberculosisin Two Infected Dairy Herds

Vaccination against paratuberculosis of all newborn animals has been performed since April 1984 in two dairy herds with a high incidence of clinical cases of paratuberculosis, using a vaccine containing heat-inactivated M. paratuberculosis in a water/mineral oil emulsion. Animals slaughtered between April 1984 and January 1991 were included in the study. Histology, bacterioscopy and culture on Smith and modified Löwenstein-Jensen media were performed using jejunum, ileum and draining lymph nodes. The animals present on the farm in April 1984 constituted a retrospective non-vaccinated group, giving an indication of the initial infection rate. After vaccination, the percentage of animals culled for clinical paratuberculosis decreased significantly (7.8 to 1.8%; P < 0.005), as did the percentage of animals with positive histology (11.8% to 5%). The incidence of infected animals, defined by positive results in histology and or bacterioscopy and/or culture, however, increased from 21.8% to 25.9%.