BILLINGS, Mont. - Seven cows traced to a Bridger ranch - including one shipped to Iowa - have tested positive for the livestock disease brucellosis, state officials said Friday.

If a second herd is found to have the disease, which causes pregnant cattle to abort their calves, Montana could lose its coveted brucellosis-free certification from the federal government. That would force a prolonged and costly testing and vaccination program for the state's 2.5 million cattle, state officials and industry representatives said.

The source of the outbreak near the small community just north of the Wyoming border is under investigation by Montana and federal agriculture agents. State officials said that will include testing of other herds that might have come into contact with the diseased one to determine if the brucellosis already has spread.

Brucellosis was thought to be eradicated from livestock in Montana in 1985. But the disease persisted in elk and bison herds in and around Yellowstone National Park, and recent outbreaks in two neighboring states, Idaho and Wyoming, were linked to elk.

"We are concerned about our brucellosis-free status," Gov. Brian Schweitzer said. "Federal and state agencies are investigating the test results now, and we will continue to work toward solutions to keep Montana's brucellosis-free status."

The likelihood that the outbreak originated from Yellowstone's bison was characterized as "remote" because of the extreme measures state and federal officials have taken to keep the animals separated. That includes slaughtering bison that wander onto rangeland.

A link between elk and the diseased herd remains a possibility, state officials said.

Almost 300 cows from the affected Bridger herd will be quarantined until the investigation is complete, state Department of Livestock officials said. The U.S. Department of Agriculture requires the herd to be slaughtered within 60 days for the state to keep its brucellosis-free status.

Even if the outbreak in Montana is limited to a single herd, the perception of the state's livestock industry could suffer, said Jay Bodner, with the Montana Stockgrowers Association. Errol Rice, the association's vice president, added that it was "presumptuous" for state officials to discount a possible connection with Yellowstone bison pending the results of the investigation.

Sen. Max Baucus, D-Mont., said Friday the state must "do all we can" to protect the reputation of its livestock and what he called the "cachet" Montana beef has on the market.

A brucellosis outbreak in northwest Wyoming beginning in 2003 cost that state's livestock industry millions of dollars and prompted neighboring Colorado to temporarily close its borders to Wyoming cattle, said Jim Magagna, vice president of the Wyoming Stock Growers Association.

Wyoming finally regained its brucellosis-free certification from the federal Department of Agriculture last September, said Teresa Howes with the U.S. Department of Agriculture.

But the consequences of the outbreak are still being dealt with through more aggressive testing and vaccination programs, Magagna said. The state has spent $4 million on the programs to date, and livestock producers have suffered an additional $5 million in losses, Magagna said.

And with the disease still present in wildlife, he said another outbreak could occur.

"None of us see the light at the end of the tunnel as to how we can actually eliminate brucellosis in the greater Yellowstone area because of the wildlife side of it," Magagna said.

Idaho lost its brucellosis-free status in 2005 and has yet to regain it. The only other state not brucellosis-free is Texas.

The first sign of the Montana outbreak came in early May, after a shipment of 51 cows from the Bridger herd was sent to Iowa via Baker, Mont., state officials said.

An initial screening test performed in Baker indicated brucellosis in a single cow. But the results came back after the shipment already had left for Iowa, where a more accurate tissue sample test done at Iowa State University on May 8 confirmed the disease.

The Montana Department of Livestock traced the diseased animal to a herd of 301 cows in Bridger, where results from tests on six more animals came back positive Friday.

The 50 surviving cows from the Iowa shipment will be slaughtered, said Dustin Vande Hoef with the Iowa Department of Agriculture and Land Stewardship.