Montana: Brucellosis found in Madison County Herd

Helena, Mont. – On Monday, December 30th the Montana Department of Livestock reported that a single cow on a Madison County ranch within Montana’s brucellosis Designated Surveillance Area (DSA) has been confirmed positive for brucellosis.

The brucellosis-infected cow was identified during a voluntary whole-herd test. The animal was euthanized, and infection was subsequently confirmed at the National Veterinary Services Laboratories in Ames, Iowa when the bacteria was cultured from tissue collected from the animal. The ranch has been placed under quarantine and an epidemiological investigation has begun. All other animals on the ranch tested negative for the disease.

State Veterinarian Dr. Marty Zaluski, Montana Department of Livestock, said the discovery of the single animal provides evidence that annual whole herd testing is an effective method for DSA producers to protect themselves. Among other benefits, early detection helps to prevent disease spread within a herd, minimizing the time needed to clean up a herd and remove quarantine. The positive animal was tested negative the prior year.

“It can be concerning when a brucellosis affected herd is discovered, but our DSA producers and veterinarians should be commended for their efforts and compliance with regulations,” Zaluski said. “A high rate of testing, much of it voluntary, is the primary reason we continue to find affected herds rapidly, which not only minimizes the impact on that producer but protects our state and our trading partners,” Zaluski added.

Past cases of brucellosis in livestock were the result of transmission from infected wild elk as determined by an epidemiological investigation that included genetic fingerprinting (genotyping) of the cultured bacteria.

This is the 10th brucellosis affected herd found since the creation of the DSA in 2010. Prior to the creation of the DSA, if two or more affected herds were detected in a two-year period, the State would have lost brucellosis Class Free Status. Due to the current USDA regulations and Montana’s DSA, our state is not at risk of dropping in Class Status.

The mission of the Montana Department of Livestock 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

–Montana Department of Livestock