Spread and control of Johne’s disease in a dairy herd
This graph depicts a computer simulation of different methods for control of Johne's disease. It is based on a herd of 100 milking dairy cattle where one cow was infected with M. paratuberculosis at the start of the simulation (year 0), and a control program was started when the prevalence of infection in the herd reached 10% (year 11).

The model illustrates:

1. It takes many years for the a M. paratuberculosis infection to reach 10%.
   
2. Once it gets started, the infection spreads quickly.
   
3. Different methods of control decrease the prevalence of infection at different rates.
   
4. The fastest method of infection control results when animal husbandry changes are made AND a test-and-cull program is instituted.
   

Disclaimer: This is only a mathematical model based on probability statistics and epidemiology. It is not designed to predict real results in herds; successful control of Johne's disease may be accomplished much faster or slower depending on many conditions specific to each farm or herd. Models of this type are most useful to demonstrate concepts and relationships for teaching purposes.