Abstract
Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease, a chronic progressive enteritis. It is generally assumed that calves rarely shed MAP bacteria and that calf-to-calf transmission is of minor importance. The objectives were 1) to estimate the prevalence of MAP-shedding young stock in MAP-infected dairy herds, and identify predictors for test-positive young stock; and 2) to estimate proportions of MAP-contaminated young stock group housing pens and air spaces, and furthermore, identify predictors for test-positive pens. Fecal samples were collected from 2606 young stock on 18 MAP-infected dairy farms. Environmental fecal samples were collected from all group-housing pens and dust samples were collected from all barns. All individual samples were analysed using IS900 and F57 qPCR; fecal samples positive by either PCR and all environmental and dust samples were cultured. Overall, 8.1, 1.2 and 2.0% of cattle were positive on IS900 qPCR, F57 qPCR and bacterial culture, respectively. Young stock housed on farms with culture-positive environmental samples collected from adult cow housing and manure storage had higher odds of testing IS900 qPCR-positive than young stock housed on farms with only negative environmental samples. Furthermore, 14% of collected environmental samples, but no dust samples, were test-positive. Age of cattle in the pen was a significant predictor for environmental sample results. Young stock excreted MAP bacteria in their feces which provided strong evidence for calves as sources of within-herd transmission of MAP on dairy farms known to be infected with this organism.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0192-1) contains supplementary material, which is available to authorized users.
Highlights
Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease (JD), a chronic progressive enteritis in ruminants [1]
Herds Based on the average herd size of 145 cows in Alberta [23], it was expected that 10 cattle within an age range of three months would be available for sampling at any point in time in each herd, which would result in an overall total of 180 cattle in this age group, a sample size sufficient to detect a minimum prevalence of 2% [24]
The environmental sample culture result was used as the outcome and the percentage MAP shedding calves was included by using either percentage of 1) IS900, 2) F57, or 3) culture-positive cattle in a pen (0, 1 – 20%, or > 20%) as predictor
Summary
Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease (JD), a chronic progressive enteritis in ruminants [1] This disease is common in dairy herds and causes substantial economic losses through decreased milk production and slaughter value, and increased risk of premature culling [2,3]. Frequency of shedding as well as fecal concentrations of MAP bacteria increase [7,8]. The objectives were: 1) to estimate prevalence of MAP shedding young stock in MAP-infected dairy herds, and identify predictors for test-positive young stock; and 2) to estimate proportions of MAP-contaminated young stock group housing and air spaces, and identify predictors for test-positive pens
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