Farmers and ranchers won't be forced to register their cows, pigs and chickens in a nationwide database aimed at helping track the outbreak of disease, the Bush administration said Wednesday.

Hoping to dampen widespread opposition to the animal tracking program, the Agriculture Department has decided it should remain voluntary.

"Really embracing this as a voluntary program ... will help the trust issues that some farmers and ranchers have raised about the national animal identification system," said Bruce Knight, undersecretary for marketing and regulation.

"I'm certainly hoping to move beyond some of the very emotional debates on animal ID," Knight said in an interview with The Associated Press.

First promised in response to the discovery of mad cow disease in this country, the tracking system would pinpoint an animal's movements within 48 hours after a disease was discovered.

Investigators never found all 80 of the cattle that came to the U.S. from Canada with the infected dairy cow that became the country's first case of mad cow disease in 2003.

Many cattle ranchers are wary of the program because they want records kept confidential and don't want to pay for the system. The industry estimates it could cost more than $100 million annually.