Farm management and soil risk factors are known to effect ovine Johne's disease (OJD) prevalence, but little is known about their impact after adjusting for each other. This study aimed to evaluate both sets of factors simultaneously in 92 sheep flocks in Australia in 2004-05.

Pooled faecal samples were collected from an identified cohort of sheep in every flock to estimate OJD infection status and soil samples from the paddocks grazed by this cohort of sheep to measure soil characteristics. A questionnaire was administered to farmers by face-to-face interview to obtain information about husbandry and management factors. Multivariable ordinal logistic regression, generalised- and general-linear mixed model analyses were conducted to test the simultaneous association of management and soil factors with OJD.

Both farm management and soil risk factors were significant in the final models. OJD prevalence was higher in sheep whose dams were maintained at a higher stocking rate and had lower condition scores during lambing. Prevalence was also higher in flocks that grazed sheep along the roads shared by neighbours and that had adopted some OJD control practices. Soil organic carbon%, an indicator of soil organic matter content, had a positive linear association with OJD prevalence.

Our results suggest that both farm management and environmental factors are important in the epidemiology of OJD. Implications of the study results for OJD control programmes will be discussed.