Billing, MT -

Yellowstone National Park administrators say shooting wild bison with vaccine-laced "biobullets" to prevent the spread of an animal disease would be too ineffective to justify the expense.

Tuesday's announcement means a program that has led to the periodic capture and slaughter of thousands of migrating bison will continue.

For more than a decade, wildlife officials have weighed shooting Yellowstone bison with absorbable, vaccine-laced bullets to prevent the spread of the disease brucellosis to livestock. The concept was supported by cattle ranchers.

About half of Yellowstone's 4,600 bison test positive for the disease, which causes pregnant animals to prematurely abort their young.

Yellowstone's chief scientist, David Hallac, says vaccinations would cost $300,000 annually but do little to drive down infection rates. A final decision will be announced after a 30-day public review period.