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Livestock at a ranch in Madison County are undergoing quarantine after an animal there tested positive for brucellosis, Montana officials announced on Wednesday afternoon.

The Montana Department of Livestock received a notice Wednesday that an animal from a Madison County herd located in the state’s brucellosis Designated Surveillance Area had tested positive for the disease.

A whole herd was tested for brucellosis in December, but the positive animal tested as “suspect” at that time. Pathologists from the Montana Veterinary Diagnostic Laboratory forwarded the samples to the National Veterinary Services Laboratories in Ames, Iowa, where the positive result was confirmed.

The Madison County herd is the 11th brucellosis-affected herd detected since Montana’s DSA was first created in 2010, the department wrote in a news release. Past transmissions have been from wild elk, but the source of the most recent infection hasn’t yet been determined.

“A high rate of testing, much of it voluntary, is the primary reason we continue to find affected herds rapidly,” said State Veterinarian Marty Zaluski in the release. “A robust testing program minimizes the impact to that operation and protects our state and trading partners.”

The positive animal tested negative a year prior, which means the Department of Livestock can lessen the scope of the investigation into the incident, staff wrote.

Brucellosis is an infectious disease that can cause domestic cattle or cattle to abort or produce weak young. It gets transmitted when animals come into contact with the birth tissues and fluids of infected animals. Humans can also contract the disease, often through unpasteurized milk products.

Humans with brucellosis can stay infected with the bacteria for the rest of their lives, and the disease is very hard to treat, said Eric Liska, brucellosis program veterinarian for the Montana Department of Livestock.

In livestock, “major abortion events can be traumatic to the herd and to the producer,” Liska said. “Owners can lose a great deal of money and potentially lose their livelihoods if their animals abort.”

Because brucellosis is difficult to detect, the Madison County herd will likely be tested two to four consecutive times, each no less than 30 days apart, Liska said. The herd must quarantine until all positive animals are removed. The final test comes after calving.

The Department of Livestock also takes steps to ensure adjacent herds aren’t affected. Past transmissions to livestock in the DSA have come from wildlife — elk, primarily — but staff still check neighboring herds.

The DSA is a large chunk of southwest Montana that spans Gallatin, Park, Madison and Beaverhead counties. The area marks the portion of the state where brucellosis exists in wildlife, and wildlife can expose cattle and domestic bison to the disease.

Ranchers who own livestock in the region must meet additional brucellosis testing and livestock identification requirements. Department staff run about 100,000 brucellosis tests each year, and that’s approximately the number of animals that utilize the DSA, Liska said.

“Our compliance has been amazing,” he said. “Producers have been just fabulous at making sure if their animals are required to be tested, they do.”

Before the creation of the DSA in 2010, if two or more herds were affected by brucellosis in a two-year period, the state would have lost its brucellosis Class Free Status with the U.S. Department of Agriculture.

Under current regulations, Montana can maintain its Class Free Status if positive brucellosis cases are detected within the DSA, since the federal agency accepts the area’s surveillance program. Poor management of the disease could trigger loss of that status, Liska said.

If Montana did lose its brucellosis Class Free Status, all cattle in the state would have to be tested for the disease before leaving the state, according to Liska. That last happened in 2008, and the state lost over $10 million, he said.

“It would be very expensive for our producers and for our state. There would be a huge loss of income and it certainly would damage our livestock industry,” he said. “We want to avoid loss of Class Free Status, and we want to make sure we find the disease as quickly as possible.”

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Helena Dore can be reached at or at 582-2628.

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