HELENA — An animal in Gallatin County recently tested positive for brucellosis, according to the Montana Department of Livestock.
According to a release, on Wednesday, December 24, the Montana Department of Livestock (MDOL) received confirmation that an animal from a Gallatin County herd within Montana’s Designated Surveillance Area (DSA) tested positive for brucellosis. This is the second detection of brucellosis in livestock in Montana in 2025. The herd has been placed under quarantine, and an epidemiological investigation is ongoing.
A brucellosis disease investigation includes looking at animal movement and contact tracing with the affected herd. The investigation may look as far as three years back into a herd’s history to ensure the disease is not present in any other livestock herds. In this case, the affected herd does not utilize shared grazing, has a minimal number of herds that run adjacent, and conducts voluntary annual whole herd testing, resulting in a relatively small scope investigation.
Voluntary whole herd testing is a valuable tool for producers. Voluntary testing allows an operation to control when animals are handled, to control when brucellosis is found (if present), to find the disease early, to minimize the risk of intra-herd spread, and to minimize the impact and duration of quarantine. The brucellosis positive animal was identified as a brucellosis suspect during voluntary fall whole herd testing. The animal was pregnant at detection and was removed from the herd before she was able to spread the disease through an abortion or during calving. Early removal allowed the required quarantine of the herd to be minimized with no expected impacts to routine management practices/movements.
“Detections of brucellosis are inevitably burdensome for an operation,” says Dr. Tahnee Szymanski, State Veterinarian. “Our goal at MDOL is that the work that DSA producers do on an annual basis can be leveraged towards a highly tailored and focused investigation that reduces the impact to an operation when brucellosis is found.”
Montana’s DSA exists due to the risk of disease spillover from infected wildlife in the Greater Yellowstone Area (GYA). Brucellosis causes reproductive issues in livestock, including abortions, still births, and neonatal mortalities. Program testing requirements help ensure that cases of brucellosis in livestock are detected before animals leave the DSA. Successful early detection helps assure Montana’s trading partners that any Montana cattle they may receive are brucellosis-free. MDOL is hopeful that trading partner confidence will result in fewer movement requirements for Montana-origin livestock and specifically for DSA-origin livestock.
This herd is the 15th brucellosis-affected herd confirmed in Montana since the implementation of the DSA in 2010. The most recent detection was within the DSA in Beaverhead County earlier this year. While the source of infection for this latest infected animal has not yet been determined, DNA genotyping and epidemiological investigations have concluded that the previous 14 infections came from wild elk. Prior investigations have also confirmed that brucellosis has not spread to neighboring herds through fence-line contact.
