The objective of this prospective longitudinal field study was to describe changes in the incidence of seroconversion, fecal shedding, and culling of dairy cows with clinical signs of Johne's disease in 6 Minnesota (USA) dairy herds participating in the Johne's Disease Demonstration Herd Project from 2000 through 2005. Implementation of this program was evaluated using an annual herd risk assessment and adult cattle were tested annually using serum ELISA and bacterial culture of feces to evaluate progress made using the control program through time. After 6 years of follow-up, there was a significant reduction in the incidence of seroconversion, fecal shedding and cows with clinical signs of Johne's disease. For 3 herds achieving recommended management changes with a risk assessment score under 30 in the last year evaluated, test results from the control program were consistent with a reduced risk of infection in calves. Further investigations including controlled trials are underway to evaluate if specific management interventions recommended within the Johne's disease control program are effective in preventing new MAP infections.