WASHINGTON – The U.S. Department of Agriculture announced Sunday that a California meat packing company had launched the recall of 135 million pounds of beef – the largest meat recall in U.S. history – following questions about the company’s treatment of cattle that were slaughtered even though they could not stand up.

The recall by the Hallmark/Westland Meat Packing Co., in Chino, Calif., covers meat produced since February 2006. USDA officials said that, given the nature of ground beef production and its shelf life, much of the recalled meat has likely already been consumed. Federal authorities said they don’t have solid evidence of illnesses linked to the meat.

Hallmark/Westland sold at least 37 million pounds of meat to the national school lunch program and other nutrition programs run by the USDA during that time, according to department officials. The Hallmark/Westland plant has been closed because of a USDA investigation of the facility’s practices.

“I am dismayed at the inhumane handling of cattle that has resulted in the violation of food safety regulations at the Hallmark/Westland Meat Packing Co.,” said Agriculture Secretary Ed Schafer.

USDA officials said Sunday that it is unclear how much of that meat has been consumed or already removed from use by federal food programs.

The department also said in its recall notice the Hallmark meat was not available to consumers through retail grocery or meat markets, but instead was sold wholesale to food companies that used it to make ground beef and products such as burrito filling, meatballs and sausage.

The USDA did not disclose where those food products were sold. Schools in Washington state and California have removed beef from their lunch menus because they suspect it came from Hallmark/Westland.

Because of wholesale distribution, it is unclear how many products will have to be recalled. USDA official stressed that Sunday’s action was a “Class II” recall, which means that there is a remote possibility of adverse health effects if the meat is consumed.

The beef industry has suffered through a difficult year of recalls, many of them caused by the presence of E coli bacteria in ground beef. In September, Topps Meats Co. of New Jersey recalled 21.7 million pounds of frozen hamburger patties after people in New York and Florida fell ill because of E. coli poisoning. Topps later filed for bankruptcy because of that recall, which involved a full year’s worth of production. The largest previous recall involved 35 million pounds of ready-to-eat meats in 1999.

While the Hallmark-Westland recall involves two years’ worth of production, the “Class II” designation means that the recall is a precaution because USDA regulations were not followed.

“In this one, we feel there is a very, very remote possibility of anyone suffering any health consequences from the consumption of this product,” said Richard Raymond, undersecretary for food safety.

The primary reason for the recall, Raymond said, was that an ongoing investigation has shown that the Hallmark plant violated USDA rules regarding the treatment of downer cattle – animals that arrive at the slaughter plant but cannot stand up because of an illness or injury.

Following the discovery of mad cow disease, or bovine spongiform encephalopathy (BSE), in the U.S. in 2003, the USDA forbade the slaughter of downer cattle in an effort to reduce the chance of BSE entering the human food chain.

Those rules were relaxed slightly last year to allow USDA veterinarians to determine on a case-by-case basis whether a downer cow couldn’t stand because of an injury, such as a broken leg, or because it was ill or diseased. Ill or diseased animals must be condemned under USDA regulations.

Raymond said the downer cattle at the Hallmark/Westland plant were examined by a USDA inspector when they were standing, but not again as required after they went down.

Schafer and other USDA officials said that it was “extremely unlikely” that the downer cattle slaughtered by Hallmark/Westland carried BSE. Raymond said that USDA has tested 750,000 cattle for BSE and only discovered two cases. USDA, however, recently scaled back the level of BSE testing it conducts, citing a lack of BSE cases.

The USDA recall follows the disclosure last month of a video secretly taped by the Humane Society of the United States. The video showed Hallmark/Westland plant workers prodding downer cattle to get them to stand, and moving downer cattle with machinery, such as a forklift.

Wayne Pacelle, the Humane Society’s president and chief executive officer, said the USDA recall would not have occurred if his group had not made the undercover video.

“This is 100 percent the trigger,” Pacelle said of his group’s video. “No one knew there was any problem at this plant.”

A California prosecutor filed animal cruelty charges against two former Hallmark/Westland plant workers last week based on an investigation prompted by the video.

Pacelle said that the recall could grow, given the fact that the Hallmark meat was used in the production of other food products.

Beef industry officials condemned the treatment of the downer cattle at the Hallmark/Westland plant. But they said the recall does not mean that the nation’s meat supply is unhealthy.

“This recall is happening out of an abundance of caution because the company did not follow regulations for non-ambulatory cattle,” said James Reagan, chairman of the beef industry food safety council. “We can say that the beef supply in the U.S. is safe. The ban on non-ambulatory or downer cattle is one of the many steps to produce safe beef, but it is not the only step.”