Two basic types of tests are available for Johne's disease: tests focusing on the bacterium (MAP) in manure and tests for antibodies in blood (the ELISA being the most common). Culture is somewhat more sensitive than ELISA at detecting infected cattle, but the ELISA is faster and cheaper. For a comprehensive discussion of diagnostic tests readers should go to the diagnostics section of this site.
Annual testing of adult cattle in the herd permits an owner to find and cull the subclinical (i.e., still healthy, but MAP-infected) cows that are shedding the organism on the premises. (The higher the ELISA result, the more likely the cow is shedding). If a whole herd test is not feasible, for a partial herd test sampling should focus on the older animals and those in poorer body condition.
If any of the cows are test-positive, their offspring still in the herd should be considered at risk for infection and should either be culled or tested annually. Because MAP bacteria are excreted not only in feces but also directly into colostrum and milk and can also infect the unborn fetus, transmission of MAP in beef cattle herds is most likely to occur from dam to off-spring rather than to other calves and herd-mates. Consequently, the highest risk of infection follows family lines: daughters of infected cows have a greater likelihood of being infected than do daughters of non-infected cows. Herd owners wishing to make most rapid progress toward elimination of Johne's disease from their herd will be well advised to cull daughters of ELISA- or culture-positive cows starting with the last daughter born and working backwards in calving history.
However, the calf rearing environment and management will greatly influence risk of infection. On operations where young calves are more confined for longer times with infected adult cattle shedding MAP in their manure, the risk of transmission from adults to non-offspring calves can be significant.
. . transmission at breeding
To "rescue" the genetics of valuable cows, embryo transfer is considered a safe means of producing non-infected calves from infected cows. Thorough embryo washing is required and careful selection of paratuberculosis-free recipients is a must.
that facilitate infection spread
While working hard to control the infection, remember not to undo all your good work by re-introducing MAP. As discussed in the Prevention section, avoid bringing cattle into your herd from unknown sources. This can happen by leasing bulls, purchasing dairy cattle (which have a higher incidence of Johne’s disease than beef cattle) for nurse cows, fertilizing pastures with manure from other herds (particularly dairy herds) or implanting a valuable embryo in a healthy-looking but MAP-infected recipient cow, who then produces an infected calf.
a) Ponds that drain contaminated pastures may harbor MAP for over a year and are very potent means of infection spread and so they should be fenced off. Clean well water in clean stock tanks should be provided. If manure-contamination of water troughs occurs, be aware when cleaning the troughs that the organism collects in the sediment. Don’t just dump it on the ground; discard it away from calves.
b) Over-crowding in wet muddy lots should be avoided, particularly during calving season. If cattle are gathered up for calving, the pasture, calving pens and the cows should be kept as clean and dry as possible. Dam and newborn calf should be removed from the calving area to a lower risk environment as soon as possible.
c) Some producers set up hutches to shelter calves during bad weather. The hutches are small enough to allow the calves to enter but too small for cows, limiting the build-up of and exposure to potentially MAP-contaminated adult manure.
d) Move your mineral feeder away from water sources, reducing congestion and heavy manure contamination in the drinking area.
e) Hay bales/rolls for winter feeding should be placed in different sites to prevent accumulation of contaminated feces in one area (areas which are often congregation sites for susceptible calves).
f) Grazing contaminated pastures is a possible means of infection transmission. Adult animals are at low risk for becoming infected by this route. Till contaminated pastures and wait for time and environmental conditions (repeated changes in temperature, minimize shaded soil by cutting grass/crops/shrubs) to kill off MAP on fields. While a majority of the organisms die within three months, a small population can remain for up to a year. Put off stocking contaminated pasture with young animals as long as feasible.
Prevention is far more cost-effective than control after infection. If herds are infected, a steady consistently applied control program will succeed and potentially eradicate the MAP infection. The foundation of a Johne's control program in cow-calf operations is a test-and-cull plan.
For information on the frequency of Johne's disease in U.S. beef cow-calf herds and recommendations from other experts on how to control Johne's disease, readers should go to the articles section of this site, or check out the brochure at www.animalagriculture.org. Just click on the “Johne’s Initiative” tab at the top of the web page.