BILLINGS, Mont. (AP) — Montana livestock officials are proposing an expansion of an animal disease zone around Yellowstone National Park after finding elk that were exposed to brucellosis.

The proposal would require cattle producers south of Dillon to ramp up herd vaccinations and take other precautions to guard against livestock infections. The area west of Yellowstone has an estimated 28,000 cattle.

Other states have imposed trade sanctions on Montana when brucellosis has gotten into cattle. But recent changes in federal regulations have lessened the sanctions when infections occur.

State veterinarian Marty Zaluski says the expansion is needed to demonstrate to other states that Montana is addressing the disease. About 46,000 cattle already are in the zone.

Brucellosis can cause pregnant animals to miscarry. It has been eradicated nationwide but persists in Yellowstone's wildlife.