Managing Bovine Tuberculosis in Minnesota’s Wild Deer
Board of Animal Health: Current Updates
Background
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In the TB management areas there have been problems with individuals talking deer outside of the TB management zone. |
Since 2005 bovine tuberculosis (TB) has been discovered in 11 cattle operations in northwestern Minnesota. The strain is consistent with bovine TB found in cattle in the southwestern U.S. and Mexico.
The Minnesota Department of Natural Resources (DNR) conducted surveillance for the disease in hunter-harvested deer within a 15-mile radius of the infected farms every fall since 2005. To date, the disease has been confirmed in 18 free-ranging deer, and eight deer sampled this winter are suspects for the disease and await final test results. All infected deer have been adult animals and were taken within five miles of a cluster of four bovine TB-infected cattle operations.
Because of these discoveries, the U.S. Department of Agriculture (USDA) downgraded the state's bovine TB status from "free" to "modified accredited advanced" in 2006. As a result, cattle producers across the state face mandatory testing of cattle and restrictions on cattle movement.
The discovery of additional bovine TB-infected livestock operations, as well as the increased number of infected wild deer, has resulted in the state dropping another level in status to "modified accredited" in 2008. The DNR is committed to assisting the Minnesota Board of Animal Health (BAH) in regaining the state's bovine TB-free status.
Current efforts to manage bovine TB in wild deer
Following the discovery of more infected deer in fall 2007, DNR decided to take more aggressive action to minimize the disease in wild deer.
In February 2007, DNR contracted with USDA Wildlife Services for assistance with deer removal within the Bovine TB Management Zone, with focus in a 140 square-mile core area that encompassed all the locations of infected deer found to-date. The primary method of deer removal by USDA in these critical areas was sharpshooting from the ground, although an aerial shooting operation was conducted in April to supplement the reduction effort.
The goal with this deer removal effort was to reduce the opportunity for deer-to-deer or deer-to-livestock transmission of bovine TB by removing potentially TB-positive deer through a reduction of deer densities in critical areas. The BAH, the Minnesota State Cattlemen's Association (MSCA), and the Minnesota Deer Hunters Association (MDHA) all support this method of deer removal and believed it was immediately necessary to accomplish our goal.
Just prior to the start of the deer removal efforts, DNR conducted an aerial survey to assess deer numbers and distribution within the Bovine TB Management Zone and the core area. This survey work was done to help guide deer removal efforts by focusing on key areas with high deer concentrations.
A population estimate of 803 ±133 deer was determined for the 140 square-mile core area alone. Even though a large number of deer were harvested from this area in 2007, DNR did not achieve a significant reduction in deer abundance from 2006 to 2007.
DNR plans to continue putting pressure on this deer herd. Liberal hunting is planned in the TB-affected area this fall but specific details are not yet available. The department also may contract with sharpshooters again next winter. Enforcement officers continue to search for illegal deer feeding sites, which can lead to enforcement investigations aimed at stopping these illegal activities.
Trained DNR staff examined all deer and lymph nodes were extracted for further testing for bovine TB. A total of 962 deer were removed by sharpshooting, including both the ground and aerial operations. An additional 125 deer were removed by landowners in the special landowner/tenant shooting zone. Eight deer were found to be suspects for bovine TB; six had clinical signs consistent with the disease and two had at least one abscessed lymph node. Final confirmation on these 8 suspect cases is expected in mid-summer. All of deer confirmed with the disease or currently suspects of bovine TB infection were harvested within five miles of previously infected cattle operations.
Future plans
DNR is currently working with BAH to assist in efforts needed to achieve split-state status from the USDA. Although DNR is again planning for a liberal hunting season in the TB-affected area, specific details of these efforts are not yet available.
DNR will continue monitoring for the disease through sampling of hunter-harvested deer. DNR is planning to conduct hunter-harvested surveillance within the larger bovine TB surveillance zone in fall 2008, with a sampling goal of 1,000 deer. This level of surveillance will continue every fall until we have two consecutive years of no positives. At that time, DNR may suspend surveillance efforts for a three-year period and then sample deer again to be sure the infection is eliminated is wild deer.
For more information on bovine tuberculosis contact Dr. Michelle Carstensen, DNR wildlife disease coordinator, (651) 296-2663
