Greeley's Swift and Co. beef plant, linked earlier this year to an E. coli outbreak, was shut Friday by federal regulators after inspectors repeatedly found manure on carcasses.
No illnesses have been reported as a result of the contamination.
The same plant, then operated by ConAgra Beef Co., was linked to 42 illnesses in eight states earlier this summer, according to the federal Centers for Disease Control and Prevention. That outbreak of E. coli 0157:H7 prompted the recall of 18.6 million pounds of ground beef produced at the plant in April, May and June.
Friday's shutdown, officially known as a "suspension action," came after repeated violations of a "zero tolerance" policy for fecal matter on carcasses, said Steven Cohen, spokesman for the U.S. Department of Agriculture's Food Safety Inspection Service.
He said the violations have occurred since mid-August at the plant, where 2,500 workers slaughter and process an average of 1.3 million cattle a year.
"I'm not surprised," said Bill Marler, a Seattle attorney who specializes in food safety cases, when he was told the plant's operations had been suspended.
Marler represents 33 people who were sickened this summer after eating contaminated beef linked to the Greeley plant.
"These plants are run that way, even when they're under scrutiny," Marler said. "It's a part of the system that is still severely broken."
Swift and Co. spokesman Jim Herlihy defended the plant.
"This is a regulatory issue," he said. "It is not a food safety issue."
He said the multistep sanitation process used at the plant would have thoroughly cleaned the carcasses even after the contamination was discovered by federal meat inspectors.
"It's not as if we were ready to ship this product, or that it was anywhere near going outside the facility," Herlihy said. "This is one point in our process where there is that inspection.
"The system does work because these evidences of contamination are found. But we have these additional steps to ensure that any product is completely safe and wholesome."
After the decision was made Friday morning, the USDA pulled its inspectors out of the plant.
After the plant's workers were told about the shutdown, most of them were sent home.
The plant was scheduled to be closed today and Sunday, and Monday was already scheduled as a "floating holiday" for workers, Herlihy said.
He said he hopes that the plant can resume operations on Tuesday.
However, the USDA's Cohen said Friday it was not clear how soon the problems could be resolved.
"There's really not a timetable," he said. "It really depends on what the establishment determines is the problem and how they propose to fix it."
ConAgra officials sold 54 percent of the company to private investors in September. It was at that point that it was renamed Swift and Co. Before being sold to ConAgra, the plant had been owned for years by the Monfort family.
Swift and Co. is the nation's third largest beef and pork processor.
E. coli 0157:H7 is a bacteria found in the digestive tracts and fecal matter of animals.
It can contaminate meat during the slaughtering process and, if ingested by humans, can cause serious illnesses, including kidney problems and bloody diarrhea. In some cases it can be fatal.
Most at risk are children, the elderly and those with weak immune systems.
Food safety experts recommend that ground beef always be cooked to at least 160 degrees to be sure that bacteria are killed.
After the massive recall in July, federal regulators issued a "notice of intended enforcement" to the plant, which required its operators to draft a written plan to deal with the problems.
The plant was operating under that new plan when the latest problems were observed, Cohen said.
The plant's operations are governed by a program known as a Hazard Analysis and Critical Control Point - or HACCP - inspection plan. That plan includes "zero tolerance" for the presence of fecal matter on animal carcasses.
"Most of the time what we're talking about is a very, very small piece of something on a carcass," Cohen said. "The inspectors felt that the repetition of these violations was an indication that the preventative measures of the plant were either inadequate or ineffective."
Cohen said it was the 128th time this year that the federal government has suspended operations at a meat processing plant.
Swift's Herlihy said the company's plan calls for meat contaminated with feces to be not only washed but also "trimmed".
"Any contamination is cut away before the process continues," Herlihy said.