BILLINGS, Mont. - A second case of the livestock disease brucellosis in just over a week has turned up in a Montana cattle herd, coinciding with new restrictions on animals exported to Texas because of worries that infections could spread beyond the region.

Friday test results from a federal animal health laboratory confirmed the latest infection in a bull that came from a herd of about 550 cattle in southern Montana's Park County, state veterinarian Marty Zaluski said.

Another case was confirmed in a Madison County cow Sept. 26, and the disease has since been found in two more animals from that 1,100-head herd.

Brucellosis can cause pregnant cattle to prematurely abort their young. It's been largely eradicated in the U.S. but persists in wildlife from the Yellowstone region of Montana, Idaho and Wyoming.

Since 2007, when Montana suffered its first livestock infection since 1985, 19 cows and 14 domestic bison in the state have tested positive for brucellosis. Zaluski says that low number demonstrates the state's costly efforts to limit transmissions through more aggressive testing are working.

But the latest back-to-back infections illustrate that brucellosis remains an active problem for ranchers in the Yellowstone area. And livestock officials elsewhere are paying attention: On Monday, a new rule goes into effect in Texas that restricts the movements of cattle imported from the Yellowstone area until they can be re-tested for the disease.

Zaluski said the rule was unnecessary and will dampen cattle sales.

Texas State Veterinarian Dee Ellis said Texas is simply trying to protect itself from a disease that plagued the state's livestock industry for decades before it was eliminated.

"You've got a wildlife reservoir (for brucellosis) that's a moving target and we weren't comfortable with just one negative test" for cattle being exported from the Yellowstone region, Ellis said. "We're just saying we want to test these animals sometime after they get here."

About 20,000 cattle annually are shipped to Texas from Montana, Idaho, and Wyoming, although it's uncertain how many come from the Yellowstone region itself, Ellis said.

The last time Montana had two brucellosis infections within a short period, in 2007 and 2008, it triggered federal sanctions that hampered livestock exports and harmed the reputation of the state's billion-dollar cattle industry.

Those rules have since been eased, but individual states have authority to impose their own restrictions.

Ellis said the Texas Animal Health Commission would pay for the additional tests that will be done on animals imported from the Yellowstone area. And he promised flexibility in the movement restrictions on the animals, which he said were not meant to be as severe as quarantine for a diseased animal.

But few producers will want to put up with the added hassle, Zaluski said.

He claimed Texas's rule was unwarranted given the additional testing put in place after Montana temporarily lost its brucellosis-free status in 2008. He also warned that the rule could set a precedent for other states because it discredits efforts by Montana ranchers and animal health authorities to effectively manage the disease.

With frequent testing, cattle producers can catch the disease soon after it's transmitted to cattle from wildlife such as elk, which protects against infections spreading unchecked within livestock herds, Zaluski said.

All of the animals infected in the two most recent cases had received brucellosis vaccinations. While the vaccinations don't protect animals from initial exposure, they can prevent miscarriages that serve to spread brucellosis when other animals come into contact with an aborted fetus.

"We've succeeded in limiting transmissions with a herd, but unfortunately you aren't able to entirely prevent infections," Zaluski said.

The infected bull from Park County was killed Sept. 23 so tissue samples could be taken after a positive field test. Testing on animals from herds adjacent to the ranches with infections are continuing in both Madison and Park counties.