(AP) A packed house filled USDA's animal ID listening session on Tuesday, where farmers called for the federal government to scrap a national livestock identification system, saying it would fail to make food safer and intrude on private businesses. The incident occurred at a USDA listening session on the proposed National Animal Identification System that was held in Missouri.

"You guys don't know what the heck you're doing," David Hannes, a farmer from Mountain Grove near the Arkansas border, told USDA employees at a town hall meeting.

USDA proposed NAIS in 2004 to ensure the safety of the nation's animal agriculture herd in the event of a disease outbreak or other contamination scenario. The point is to be able to trace an animal back through the marketing channels to its place of origin. For some industries, the record keeping, tracking and database issues are sticking points to acceptance.

USDA veterinarian David Hopson said the tracking system would help officials respond to :disease outbreaks more quickly because they would know where livestock are and have been. The system also will help open foreign markets to American meat products faster. "We need a good system in place to keep our U.S. livestock healthy," Hopson said.

Individual states decide whether to participate in the animal tracking program and whether to make farmers' participation voluntary or not.

A 2008 Missouri law bars the state Department of Agriculture from participating in a mandatory livestock tracking program without the explicit approval of the Legislature. Michigan became the first state in 2007 to make parts of the program mandatory by requiring radio frequency identification ear tags to be attached to cattle and dairy cows.

The U.S. pork industry has had an identification program in place since 1989.

USDA held Tuesday's meeting at a hotel in Jefferson City, Mo., and drew producers from Arkansas, Missouri, Illinois, Kansas and Wisconsin. It is one of several listening sessions that USDA is conducting to measure the issues involved with NAIS in the field.

Several dozen protesters, including some farmers, stood outside the hotel, while inside, the audience greeted critics with loud cheers, standing ovations and shouts of approval.

The tracking system is "irrelevant and unnecessary," said Rhonda Perry, program director of the Missouri Rural Crisis Center, which helped sponsor the protests. It will not make the nation's meat supply safer because the problems have been at the processing facilities, said Perry, who farms near Armstrong in mid-Missouri.

Others sharply criticized USDA's competency and honesty. Numerous speakers criticized government regulations that they said make it harder for American farmers to stay in business.

Steve Willard, president of the Missouri Cattlemen's Association, said no issue has triggered as much controversy as the livestock tracking system and implementing it could be a "costly mistake" given the strong opposition.

Of the 55 people who spoke in nearly four hours, only one pork producer endorsed the tracking system. Brent Sandidge, who lives in rural Saline County about halfway between Kansas City and Jefferson City, noted that pork sales plummeted during the recent Type A H1N1 flu outbreak, even though pigs weren't spreading the disease. He warned other livestock producers that one infection that is not quickly contained could ruin their industries.

"I watched swine flu destroy our markets," Sandidge said before hecklers interrupted him and he stormed out of the hotel.

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AP contributed to this story.