An animal abuse investigation at a California slaughterhouse has led to the largest beef recall in the nation's history - the bulk of which was sent to school lunch programs.

The U.S. Department of Agriculture recalled 143 million pounds of frozen beef Sunday, suspecting some of it came from steers too sick to stand up.

Up to 37 million pounds of the questionable meat went to school programs and officials fear it has already been eaten by thousands of children.

"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," said Dr. Dick Raymond, USDA undersecretary for food safety.

Raymond said no illnesses have been linked to recalled beef. Schools spokeswoman Melody Meyer could not say yesterday whether any of the recalled meat has been served in city schools.

"We will have to review the situation as more facts are known," Meyer said. "We're not going to serve any beef until we confirm that the meat is safe."

City schools are closed this week for winter break. Officials hope to have more information before school resumes Feb. 25, Meyer said.

The recall was limited to frozen beef shipped from the Westland/Hallmark Meat Co. in Chino, Calif., dating from Feb. 1, 2006.

The slaughterhouse came under fire after an undercover Humane Society video showed sick cattle being shoved with a forklift, and workers kicking and shocking steers that were too sick or injured to walk.

Secretary of Agriculture Ed Schafer said Westland/Hallmark violated health regulations by frequently failing to have veterinarians examine sick cows.