Scientists at the University College Dublin, in partnership with noted Australian epidemiologist, Evan Sargeant, and Animal Health Ireland, evaluated multiple diagnostic testing strategies for Irish dairy herds. The aim of their study was to evaluate the suitability of a range of national surveillance methods, both for case detection and for providing confidence of herd freedom from MAP infection, in terms of herd sensitivity, positive and negative predictive values, overall cost, and utility, including any logistical factors associated with their use.
Strategies the scientific team evaluated included:
- ELISA on individual milk samples from all lactating cows in a herd annually.
- ELISA on serum samples from all adult cows in a herd annually.
- ELISA on serum samples collected at slaughter from culled cows (serum already being collected for the Irish brucellosis program); with estimates made for testing 50%, 75% or 100% of culled cows.
- ELISA on bulk tank milk.
- PCR on 6 environmental fecal samples.
- PCR on pooled fecal samples (5/pool) for all adult cows.
In general, testing for the MAP organism by PCR on pooled fecal samples from all adult cows performed best, when cost was not a consideration. MAP detection at the herd-level using environmental fecal sample collection provided the best combination of herd testing accuracy and affordability.
This is consistent with findings in the U.S. where environmental fecal samples are a component of the Voluntary Bovine Johne’s Disease Control Program. Environmental fecal testing was also the basis of the last (2007) survey of U.S. dairy herds as reported by Lombard et al. (Preventive Veterinary Medicine 108:234-238, 2013.)
Readers are strongly encouraged to read the full Open Access report in the Journal of Dairy Science (volume 102, pages 1-14) to appreciate the many nuances of the findings of this excellent study.