Cattle entering North Dakota from most of Montana will have to be tested for brucellosis, a contagious disease that weakens animals, reduces milk production and results in lost pregnancies.

The State Board of Animal Health enacted the testing requirement Wednesday after seven cattle in southern Montana recently tested positive for the disease.

The brucellosis affected cattle were in Carbon County, Mont., about 300 miles from the North Dakota border. The federal government is in the process of testing additional cattle in Montana to determine if the infection is more widespread.

In debating a course of action, the board members weighed the financial impact that immediate testing would have on ranchers and livestock sellers versus the potential damage from a brucellosis outbreak in North Dakota.

They decided to make an exception for all cattle from eastern Montana, which are hundreds of miles away from the infected herd and commonly cross the North Dakota border for grazing and auctions.

State veterinarian Susan Keller said immediate testing is necessary because the financial and health consequences of a brucellosis outbreak are greater than the impact of mandatory testing.

"The impact of brucellosis is huge to the cattle industry and the bison industry," Keller said.

According to the U.S. Department of Agriculture, brucellosis would cost the U.S. cattle industry $80 million a year if left unchecked. In the 1950s, before widespread testing and education about the disease, losses averaged about $400 million, according to the USDA.

The disease is spread from animal to animal through direct contact and contact with bodily fluids. Humans also can become infected though similar contact and it is then known as undulant fever.

With education, testing and vaccines that are 70 percent to 80 percent effective, brucellosis has been largely contained in recent years, according to the USDA.

Idaho and Texas are the only states that haven't been declared free of the disease, Keller said. North Dakota received its brucellosis free status in 1982.

The testing requirement will be in effect until at least June 20, when the animal health board holds its next meeting.

(Reach reporter Jonathan Rivoli at 223-8482 or jonathan.rivoli@;bismarcktribune.com.)