Workers at the plant are also accused of animal cruelty

It comes from a company in California, which officials said allowed meat from cattle unable to stand at the time of slaughter to enter the food chain.

But the USDA said the health hazard was minimal. Much of the meat was purchased for federal nutrition programmes.

The meat-packing plant is also being investigated for animal cruelty.

The USDA had suspended operations there earlier this month after an undercover video came to light showing crippled and sick animals being mistreated.

Caution

The USDA recall affected frozen beef products from the Westland/Hallmark Meat Co in Chino, California, dating back to 1 February 2006.

We don't think there is a health hazard, but we do have to take this action

Dick Raymond

USDA

The move surpasses a 1999 recall of 35m lbs (15.9m kg) of ready-to-eat meals, which were thought to possibly be contaminated with listeria, officials said.

An estimated 37m lbs (16.8m kg) of the beef recalled on Sunday went to school lunch programmes and other federal nutrition programmes, the USDA said. Some was also supplied to major fast-food chains.

But officials said most of the recalled meat has probably already been eaten.

The USDA classified the recall as Class 2 - meaning there is a remote probability that the product could harm health if consumed - and said investigators had found no cases of illness related to the meat.

An undercover video showed cattle being prodded with a forklift truck

"We don't know how much product is out there right now. We don't think there is a health hazard, but we do have to take this action," Dick Raymond, USDA undersecretary for food safety told the Associated Press.

In a statement, Agriculture Secretary Ed Shafer said he had been "dismayed by the inhumane handling of cattle" that resulted in the violation of food safety regulations at Westland/Hallmark.

"It is extremely unlikely that these animals were at risk for BSE [mad cow disease] because of the multiple safeguards; however this action is necessary because plant procedures violated USDA regulations," he added.

'Downer cattle'

The recall was ordered after USDA officials said the plant did not consistently order "complete and proper" inspections of cattle which had lost the ability to walk prior to slaughter.

Such "downer" cattle are at greater risk of contamination by E. coli, salmonella or contracting mad cow disease, as they have weaker immune systems and greater contact with faeces than walking cattle.

A recall of this staggering scale proves that it's past time for Congress and the USDA to strengthen our laws for the sake of people and animals

Wayne Pacelle

Humane Society of the US

They should either be removed from the food supply, or receive a more thorough inspection following slaughter, officials say.

Operations at the plant had already been suspended earlier this month following the broadcast of an undercover video shot by the Humane Society of the United States.

The video showed crippled and ill animals being prodded with the blades of a forklift truck, kicked, given electric shocks and sprayed with high-pressure water hoses by staff in an effort to get them to their feet before slaughter.

"A recall of this staggering scale proves that it's past time for Congress and the USDA to strengthen our laws for the sake of people and animals," said the Humane Society's president, Wayne Pacelle.

Two former employees, including a slaughter pen manager, were charged with animal cruelty by California prosecutors on Friday. No charges have been filed against Westland/Hallmark, but the USDA investigation continues.

In a statement issued on 3 February, Westland/Hallmark president Steve Mendell said it was co-operating with the USDA and called the practices shown in the video as "a serious breach of our company's policies and training".

"We have taken swift action regarding the two employees identified on the video and have already implemented aggressive measures to ensure all employees follow our humane handling policies and procedures," he added.