Incidence of paratuberculosis after vaccination against M. paratuberculosis in 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%.