Montana Department of Livestock Reports Brucellosis Affected Herd in Beaverhead County

August 20, 2025

On Friday August 15, the Montana Department of Livestock (MDOL) received confirmation that an animal from a Beaverhead County herd within Montana’s Designated Surveillance Area (DSA) tested positive for brucellosis. The herd has been placed under quarantine pending the completion of an epidemiological investigation.

The positive bull was identified as a brucellosis suspect during required testing at a livestock market in late July. The animal was euthanized and taken for necropsy at the Montana Veterinary Diagnostic Laboratory (MVDL) where tissues were collected and sent to the United States Department of Agriculture’s (USDA) National Veterinary Services Laboratory (NVSL) in Ames, Iowa for confirmatory testing. NVSL was able to grow the Brucella abortus organism from one of the lymph nodes collected from the animal.

The disease investigation will include testing and tracing of animal contacts and movements to ensure that the disease is not present in other livestock herds. MDOL will work with the affected operation to minimize the impact of this diagnosis by conducting a tailored and focused investigation.

Montana’s DSA exists due to the risk of disease spillover from infected wildlife in the Greater Yellowstone Area (GYA). Program testing requirements help ensure that cases of brucellosis in livestock are detected before animals leave the DSA. Successful early detection provides confidence to Montana’s trading partners that any Montana cattle they may receive are brucellosis free. Brucellosis causes reproductive issues in livestock including abortions, still births, and neonatal mortalities.

“While detections of brucellosis are a hardship on operations, this detection is still a reflection of the success of our state brucellosis program,” said Dr. Brenee Peterson, MDOL veterinarian. “Through the work of DSA producers and local veterinarians, we continue to detect the disease early and prevent the export of a brucellosis infected animal to one of our trading partners.”

This herd is the 14th brucellosis affected herd confirmed in Montana since the implementation of the DSA in 2010. The most recent detection was within the DSA in Madison County in April of 2023. While the source of infection for this latest infected bull has not yet been determined, DNA genotyping and epidemiological investigations have concluded that the previous 13 infections came from wild elk. Prior investigations have also confirmed that brucellosis has not spread to neighboring herds through fence-line contact.

The mission of MDOL is to control and eradicate animal diseases, prevent the transmission of animal diseases to humans, and to protect the livestock industry from theft and predatory animals. For more information on the Montana Department of Livestock, visit www.liv.mt.gov.

Source: Montana Department of Livestock