Johne’s Disease: Control and Elimination (part 3)

– William Shulaw, Extension Veterinarian, Cattle and Sheep, Ohio State University

Controlling or eliminating Johne’s disease in a herd takes time and commitment. A final observation from the Demonstration Herd Project is that the herd owner must become well informed about the disease and set realistic goals. If this includes making rapid progress, and perhaps eventual elimination, careful consideration regarding retaining home-raised heifer replacements must be given. One of our beef herds had made the decision to try to eradicate Johne’s disease from their herd before they were enrolled in the Project in 2004. To their great credit, the owners had recognized the possibility that a replacement heifer could become infected as a calf and not begin shedding for several years. This could destroy a lot of hard work and expense after considerable progress toward that goal had been made by exposing a future calf crop to MAP. Before 2004, they made the decision not to keep their own heifers until they had reason to believe the disease was gone or nearly so. Toward that end, they have purchased some heifers from a herd enrolled in Ohio’s Test-Negative Status Program. After removal of two cows following the first sampling in the fall of 2004, and one more after sampling in the spring of 2005, they have had six consecutive, semi-annual, whole-herd tests with all negative culture and blood test results.

In contrast, the other beef herd could not afford to make the decision not to keep some of their own heifers, but they do wish to eventually eliminate Johne’s disease from the herd. About 20% of the cows were culture-positive on the first test in the fall of 2004 and 8% the following spring. Subsequently, semi-annual cultures revealed one or two positive cows per sampling. In 2007 all tests were negative. However in the spring of 2008, the apparently healthy, but heavy-MAP-shedding, home-raised heifer cited in the above example of environmental contamination was detected. This is very disappointing but not really surprising. Actually, although it is hard to see any good in this, it is better to have found her as a two-year-old than as a three or four-year-old. This is one of the many frustrating aspects of this insidious disease.

To summarize, some take home messages for beef producers from this Project include:

* Cows shedding MAP into the environment can make the udder of many of their herdmates sources of infection for the calves.

* Beef cattle herd owners need to carefully consider the timing of any diagnostic testing so that results will be available with sufficient time before the calving season begins to cull or segregate infected cows and to remove potential contamination from the calving area before the new calves arrive.

* Pooled sample manure culture can allow the producer and the veterinarian to better characterize the extent of MAP infection in the herd than using blood testing, and they can then determine if there are individual animals that should receive further testing to identify the infected ones.

* The herd owner must become well informed about the disease and set realistic goals in light of their individual situation and current technology.

Direct Federal and state support to producers for control of Johne’s disease has dwindled to nearly nothing. However, several million Federal dollars have been allocated for research on the disease over the last five years, and on a worldwide basis, attention on this important disease is increasing in both the livestock and human health sectors. In Ohio, we have been evaluating the usefulness of testing breeding age heifers to find infected animals early in life as well as the potential uses of a more rapid test on manure, the PCR assay. Last April, the National Animal Health Monitoring System released its Dairy 2007 report which showed that at least 68% of US dairy farms are infected. Among other information, the report also states, “These results suggest that at least one-fourth of U.S. dairy operations may have a relatively high percentage of infected cows in their herds.” The available information suggests that the situation is not yet so serious for the beef cattle industry. The national Johne’s Disease Demonstration Herd Project has given us new insights into the control of this disease, and additional information is expected from analysis of the national database that now exists from this project. We hope beef producers will take advantage of what we know about prevention and control of this disease to reduce spread within and between their herds.