State officials and the owner of a Paradise Valley cow recently sickened with brucellosis this week quashed a rumor that brucellosis came to Montana from exotic Mexican cattle, not local wildlife.

"Absolutely not," said Christian Mackay, executive officer of the Montana Board of Livestock. "(Mexican cattle) were not the source of the outbreak."

Brucellosis appeared last week for the second time in 18 months in Montana cattle. That will cause the state to lose its brucellosis-free status and could be a multimillion dollar hit to the state's cattle economy.

Brucellosis is a serious disease of ruminant animals, such as cattle, bison and elk, that can cause females to abort their calves. Federal policy has long called for eradicating the disease from U.S. livestock and it is rare in the United States.

However, brucellosis persists in bison and elk in and around Yellowstone National Park, where wildlife decades ago contracted it from domestic stock. Montana, Wyoming and Idaho all have had recent cases of the disease and are part of a complicated federal and state plan intended to keep bison from spreading the disease to domestic animals. That plan does not involve elk, which can also spread the disease.

The Mexican-source rumor evidently sprung from the fact all of the cattle that have come down with brucellosis in Montana were either a certain Mexican-associated breed of cattle called Corriente or had contact with Corriente.

Mexico is not brucellosis free.

The disease first appeared in Montana cattle at a ranch near Bridger in May 2007. Some of that herd was Corriente, Mackay said, some was Angus and others were cross bred with Angus. No Corriente on that ranch were from Mexico, Mackay said. State and federal investigators did an extensive genealogical study of those cattle, particularly the Corriente. They traced the Corriente cattle back several generations, never coming across an ancestor from Mexico.

Instead, he said, all those cattle came from Montana or Wyoming, and none had brucellosis.

That same herd had also spent some time at a ranch near Emigrant, near Yellowstone.

A similar investigation is now under way for the most recent outbreak, which also affected a Corriente cow.

Art Burns, owner of the cow, said the animal was born and raised in Montana.

The U.S. Animal and Plant Health Inspection Service also did a genetic analysis of tissue from one of the cattle infected in 2007. They concluded the disease did not come from fellow cattle, said Rachel Iadicco, an APHIS spokeswoman, a finding that runs counter to the Mexican theory.

The agency did not run similar DNA tests on all the infected cattle in the Bridger outbreak, she said, because typically such tests show the same results for all animals in an infected group.

The Mexican theory seemed to have two major proponents: The most vocal is bison and wildlife groups who oppose the current brucellosis management plan, which focuses solely on bison and, at times, calls for killing them. The rumor also spread through the state's stock growing community, perhaps because Corriente are not raised for beef and may have a lower status in the eyes of beef producers.

The Buffalo Field Campaign, which has long called for protecting, not slaughtering bison, issued a release after the second outbreak suggesting Corriente were behind the disease. Another wildlife group, Buffalo Allies of Bozeman, put out a release calling for Gov. Brian Schweitzer to pull out of the current brucellosis management plan because Corriente, not bison, were behind the outbreak.

Chris Klatt, of Buffalo Allies, said he sent out the release because he heard Corriente were involved. Klatt said he didn't know the latest Corriente cow to be sickened was from Montana, not Mexico.

Errol Rice, executive director of the Montana Stockgrowers Association, said he heard the Corriente theory from some in the cattle industry, but dismisses it.

"As soon as they hear the word 'Corriente,' that's the first knee-jerk reaction," Rice said. "But none of those cattle were actually imported, the probability of them contracting it from Mexico is pretty much zero."

Other than the popular associations with Mexico, there is nothing about Corriente that renders them uniquely susceptible to brucellosis, said James Spawn, of the North American Corriente Association in Kansas City, Mo.

His organization has 900 registered Corriente breeders across the United States. Spawn said he didn't know of any American Corriente infected with brucellosis except the ones in Montana's greater Yellowstone area.

He also said the idea that all Corriente are from Mexico is patently false. Corriente are the descendants of cattle brought to the New World from Spanish and other European explorers. The animals were generally allowed to range freely and evolved into a unique species, known to be smaller and heartier than beef cattle, which have been bred for muscle mass.

Beef cattle largely replaced Corriente, although a few persisted in a nearly wild state in Central and South America with a few outliers in the southern United States.

Today, the breed has been formalized and are mostly bred for rodeo stock, Spawn said. Corriente are used in team roping and calf wrestling. Both males and females have horns.

The animals have gained popularity among some few beef producers, he said, because they are heartier than many traditional breeds and can deliver their calves without human assistance. Their use in the beef industry is limited, he said, although most rodeo stock eventually ends up on a dinner plate.

Corriente are also not a foreign breed to Montana. A past president of the North American Corriente Association and current member of the group's advisory board is a rancher from Garryowen.

Reporter Jennifer McKee: 443-4920 or jennifer.mckee@lee.net