Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne's disease (JD), a chronic, nontreatable enteritis of ruminants. The pathogen causes substantial losses to the dairy industry and might be associated with Crohn's disease in humans. Eradication of MAP through programs that are solely based on 'test and cull' is ineffective because current tests lack sufficient accuracy for reliable detection of infected cattle. Consequently, current MAP control programs focus on prevention of new

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... infections through implementation of best management practices. The overall aim of this thesis was to evaluate the Alberta Johne's Disease Initiative (AJDI), a management-based MAP control program. Research in this thesis focussed on estimating MAP herd-prevalence, evaluating environmental samples as a diagnostic tool, identifying risk factors for MAP infection, and identifying factors that influenced management improvements. A total of 370 farms participated in the AJDI and were visited annually by their herd veterinarians who conducted risk assessments, collected environmental fecal samples, and discussed management changes. Sixty-eight percent of Alberta dairy farms were MAP-infected and environmental samples collected from lactating cow alleyways and manure lagoons were most frequently culture-positive, suggesting that these samples are important to guarantee high environmental sample accuracy. Furthermore, farms with manure-contaminated cattle and pens, poor feed hygiene, or high purchase rates and low purchase precautions were more likely to be MAP-infected; therefore; improvements in these management areas might be most effective in controlling the spread of MAP. Although most farms subsequently improved management, positive test results and agreed management changes increased the rate of management improvements (which were cost effective). It is noteworthy that the current program overlooks hygiene of young cattle, because 2% of heifers shed MAP which indicates that management improvements in this area may reduce M [...]