"Somebody in authority looked at this scenario and said, there's been meat going through the system that shouldn't," said Bill Marler, a prominent food safety attorney in Seattle who is not directly involved in the matter.

The USDA has not received any reports of illness linked to the meat, an agency spokesman said Wednesday.

The government's allegation was strongly denied by Robert Singleton, one of Rancho's owners.

Singleton, who on Thursday made his first public comments on the investigation, acknowledged there were days each week when he wasn't at the property. But he insisted Rancho consistently slaughtered animals in accordance with the USDA's rules.

"There was always an inspector on the property," he said. "We never harvested without an inspector on site."

Experts said the USDA's statement suggested exactly the opposite.

"It could mean that perhaps animals had been railed out for further inspection and that wasn't complete yet and when an inspector wasn't present those animals were processed," said David Theno, CEO of Gray Dog Partners, a Del Mar food industry and safety consulting firm.

Theno was formerly a senior vice president and chief food safety officer for Jack in the Box, Inc., which he joined after it was enveloped in scandal when its burgers were blamed for a massive outbreak of food poisoning.

"The agency virtually never takes this kind of action unless they've got pretty solid information to act on. This is big time stuff," he said.