This prospective longitudinal observational study was conducted to evaluate the effect of a standardized control program on the incidence of Johne's disease in 8 dairy herds in Minnesota. Depending on recruitment year, herds were followed for between 5 and 10 yr. Program compliance was evaluated using a cohort risk assessment score by birth cohort. Fecal samples from cows in study herds were tested annually using bacterial culture to detect Mycobacterium avium ssp. paratuberculosis (MAP), and serum samples from study cows were tested using an ELISA to detect antibodies to MAP. Clinical Johne's disease was also recorded. Cohort risk assessment score decreased along birth cohorts. Depending on the follow-up period in each herd, 5 to 8 birth cohorts were followed to describe changes in time to MAP bacterial culture positivity, serum ELISA positivity, MAP heavy shedding status, and clinical Johne's disease. The analysis of time to bacterial culture positivity, serum ELISA positivity, heavy fecal shedding status, and clinical Johne's disease using a time-dependent Cox regression indicated a reduction of the instantaneous hazard ratio by birth cohorts and by cohort risk score; however, the strength of association between the cohort risk score and each of the 4 disease outcomes decreased over time. The age at which the cows first tested positive for bacterial culture, serum ELISA, and heavy fecal shedding, and the age of the cows at onset of clinical Johne's disease signs remained constant for all birth cohorts. Based on herd risk scores, overall herds complied with the recommended management practices in the program. Results were consistent with a within-herd reduction of Johne's disease transmission, and that reduction was associated with herd-level management practices implemented as part of the control program.
Bibliographical noteFunding Information:
We thank the study herd owners, managers, and employees for their participation and enthusiastic collaboration with the disease control program. We also thank the Minnesota Board of Animal Health district veterinarians and staff for their collaboration and support of the JD demonstration herds, and the Minnesota Veterinary Diagnostic Laboratory (St. Paul) for diagnostic testing and sample storage. We acknowledge the anonymous reviewers for their time and suggestions to improve this manuscript. Finally, we thank the USDA-APHIS Veterinary Services and the Johne's Disease Integrated Program funded by USDA National Institute for Food and Agriculture (Washington, DC) for providing partial funding for this study.
Copyright 2012 Elsevier B.V., All rights reserved.
- Disease control program
- Johne's disease