Johne's Disease

In response to feedback from the veterinary community and members of the cattle industry, the Department of Livestock (DOL) is increasing education and outreach efforts about Johne’s Disease.

Johne’s is a contagious and usually fatal bacterial disease that primarily affects the small intestine of cattle and other ruminants. The Johne’s bacterium (Mycobacterium avium subspecies paratuberculosis (MAP)) is primarily spread between animals through feces.  Clinical signs of the disease include diarrhea and weight loss, despite a normal appetite and are rarely seen until two or more years after initial infection, which usually occurs within 6 months of birth. As an animal ages, susceptibility to MAP decreases and a larger dose of the bacteria is required for infection.

To better understand the prevalence of Johne’s disease in Montana, we reviewed recent Johne’s testing data from 2017-2019. Our findings highlight a lack of knowledge about the occurrence of Johne's in Montana. The number of cattle tested within the three-year period is low. More, positive cases are being diagnosed despite the low numbers of cattle tested. Only 0.3% of Montana’s cattle herd was tested between 2017-2019, yet 146 premises were identified as having Johne’s disease.

Johne's Testing Data

The map below represents Montana Johne's tests for FY25 (7/1/2024 - 6/30/2025) by county.  Click the map to display the interactive map with more in-depth detail.

The chart below (Chart 1) displays Johne’s testing in the top twenty counties based on cattle inventory. Cattle inventory is shown with the cow icon and the percent of cattle tested is represented by the orange bar. Readers should note that less than 3% of cattle were tested in all counties included below. The data source for cattle inventory by county is 2019 Per Capita Data.

Chart 1.  Percentage of cattle tested for Johne's based on cattle inventory

To emphasize the risk of low testing activity, below is summary of animal movement from a single Montana premises. This case shows how quickly Johne’s disease can spread through cattle sales and movement.

Data was gathered from a single operation with a history of Johne’s positive animals. All data represents primary sales from the source operation to customers, between January 2015 and May 2018. The number of customers purchasing animals from the source operation may be an underestimate and do not account for cattle buyer sales and further distributions. During this time period, the source operation sold cattle to 225 individual customers, 139 of those were in-state and 86 out-of-state. A total of 1795 cattle were sold, 888 of those in-state and 907 out-of-state.

The maps below (Figure 1 and 2) show the Montana counties, states and countries receiving cattle from the source operation over the four-year period.

The chart below (Chart 2) breaks down the number of customers who purchased cattle and the number of cattle sold, by year.

Chart 2.  Number of cattle sold by one Johne's positive operation between 2015-2018

Johne's Disease is particularly concerning in the seedstock sector of the cattle industry.  As mentioned above, most animals are infected while they are calves but do not present with signs of the disease until later in life.  Animals such as replacement females or bulls, may be infected when purchased, despite appearing healthy.