David J. Wilson, Kerry A. Rood, Jennifer Bunnell, Chelsea Whitehouse, Todd M. Byrem, Gregory M. Goodell
Dairy herd-level prevalence of Mycobacterium avium subsp. paratuberculosis (MAP), causative agent of Johne’s disease (JD), Mycoplasma spp., and Bovine Viral Diarrhea (BVD) virus were estimated in Utah and surrounding states and compared to previous surveillance results. Milk was collected at 3-4 day intervals on 5 dates (duplicate samples) from each bulk tank on participating farms, samples analyzed separately. One frozen sample was shipped to a laboratory for JD/MAP testing with ELISA and real-time PCR, the other paired sample was shipped to another laboratory for mycoplasma and BVD testing. Mycoplasma was cultured on modified Hayflick medium, standard methods; BVD testing was real-time, RT-PCR. 151/209 (72%) eligible dairy farms participated. Farms detected positive (some had multiple diseases) were: 58 JD (38%); 4 mycoplasma (3%); 14 BVD (9%). Sensitivity of testing was: 284/528 milks = 54% for JD, 17/61 = 28% for mycoplasma (lower than previous reports), 41/117 = 35% for BVD. Of 67 herds positive for JD in 2009, 28 (42%) remained positive, 14 (21%) became test-negative, and 25 (37%) were lost to follow up. Of 16 herds positive for mycoplasma in 2007, one (6%) remained positive, 8 (50%) became testnegative, and 7 (44%) were lost to follow up. Bulk milk remains a practical way to screen dairy herds for presence of JD, mycoplasma and BVD, provided that repeated sampling is used. Mycoplasma-positive herds were more likely to become test-negative in bulk milk in subsequent years than were JD-positive herds. Prevalence of BVD was similar to but slightly lower than previously reported.
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