BILLINGS, Mont. -- DNA testing points to elk as the most likely source of a recent livestock disease infection near Yellowstone National Park, according to a federal report.

Brucellosis is a bacterial disease that causes cows to prematurely abort their young.

Efforts to guard against its transmission -- largely through periodic slaughters of Yellowstone bison -- have proven ineffective: Seven cases have been confirmed in recent years in Montana, Idaho and Wyoming.

The disease has been eradicated elsewhere in the country.

Thursday's report from the National Veterinary Services Laboratory in Ames, Iowa, said the brucellosis strain found in May in a cow in Pray, Mont., "appears to be similar to strains recovered from bison and elk."

The cow had no contact with bison, according to state officials. The report was released by Montana State Veterinarian Marty Zaluski and laboratory officials could not be reached immediately for comment.

"This is the smoking gun we were looking for," Zaluski said. "We're not really happy to attribute this to any one species or another, but it does give us direction as far as where we need to conduct the risk mitigation."

The role of elk in spreading brucellosis to cattle has raised tensions between livestock producers and sporting groups worried over the potential for reductions in herd sizes. It has also fueled an interstate argument over Wyoming's use of artificial elk feedgrounds, which concentrates the animals in small areas and allows the disease to circulate within herds.

In Montana, state wildlife officials have started laying the groundwork for expanded wildlife disease testing and more public hunting, to cut down elk numbers and keep them out of areas with cattle. Those efforts could start as soon as this fall.

Last week, Montana Fish, Wildlife and Parks Commissioners doubled the quota for a possible special management hunting season around Yellowstone, to 2,000 elk.

That number represents the ceiling of any hunt that might be adopted, said Pat Flowers, Fish Wildlife and Parks regional supervisor for the Yellowstone area.

Flowers said he accepted the federal findings on elk "at face value," but added that his agency will seek its own analysis to confirm the report.

"If this proves to be true, we need to look at how do we either change population numbers or change how elk are distributed on the landscape," Flowers said.