Bison in Yellowstone. Officials are renewing their attention to bison as the source of the disease brucellosis after a string of infections in livestock.

In the frigid January of 1997, dozens of hunters for Montana’s Department of Livestock stalked the border of Yellowstone National Park looking for bison. Against the stark winter landscape, it was easy for the hunters to spot the giant, humpbacked beasts. As the animals crossed over the invisible park border, the hunters aimed Winchester Model 70 rifles at their lungs.

Shots snapped, and hundreds of bison dropped to the snow. Many, wounded in their guts and rumps, needed second and third slugs before they were killed. Although the meat was to be donated to local Native Americans, some members of those very tribes came to protest the slaughter. A park ranger described these grisly scenes as a “free fire.”

Behind the mass hunts were Montana’s cattle ranchers. The ranchers considered bison to be the biggest threat to what is today a $3 billion annual agribusiness industry in the state. Killing bison that left the park’s territory was the only way, they believed, to protect Montana’s famous beef cattle from a disease called brucellosis. That condition can cause cows to abort and lose weight (read: meat). As with any meat-borne bacteria, the least trace of brucellosis can tarnish the reputation of any state’s supply of beef. But the problem with killing the animals that are seen as its carriers, critics say, is that no Yellowstone bison has ever given brucellosis to a cow.

Nevertheless, on Feb. 12, days after passage of the latest farm bill, Yellowstone officials began shipping bison to slaughterhouses and said they will soon kill as many as 600 more, for the same reason as ever: to protect cattle from brucellosis. The version of the bill President Barack Obama signed on Feb. 7 bundles millions for brucellosis surveillance, testing and vaccine development — which animal activists fear could lead to more bison killings — into a larger pool for academic research. That amount is $3.5 billion, part of the astronomical $956 billion farm bill.

Livestock officials believe the funding could lead to a breakthrough that helps all animals.

"The hope would be to move toward assuring that we effectively prevent brucellosis in livestock,” said Jim Magagna, executive vice president of the Wyoming Stock Growers Association, “and control it in wildlife."

But wildlife advocates say that because so many Yellowstone bison have been killed under the dubious guise of protecting cattle from brucellosis, any new spending lobbied for by the cattle industry is a threat to wildlife. They say that brucellosis management is unfair and riddled with inconsistency. It is a waste, they say, to spend more money without reconsidering bison management.

“This is politics, this is not just dealing with a disease,” said Kathryn QannaYahu, a Montana hunter and environmental activist.

Since 1985, more than 7,000 Montana bison have been killed from a Yellowstone herd that now totals around 4,500. (Other animals, such as Wyoming elk, have been killed too.) This has infuriated environmentalists, who have watched bison numbers restored from virtual extinction.

Sen. Mike Enzi, R-Wyo., slipped $35 million for brucellosis work into the Senate’s version of the farm bill. The sum astounded some researchers. The Wyoming Stock Growers Association and others lobbied for the funds in part because brucellosis study slowed after Sept. 11, 2001. The Department of Homeland Security flagged the bacteria as a potential tool for terrorists. It can cause flulike symptoms in humans, though it is now rare in developed nations. It is less severe in wildlife, veterinarians say.