Days after the largest beef recall, the Agriculture Department said Thursday that more than a third of the contaminated meat had been used in federal nutrition programs, including school lunches.

Of the 143 million pounds of recalled meat, just over 50 million pounds was bought for use in the federal programs, the department said. About 20 million pounds of that has already been consumed. A further 15 million pounds has been located and will be destroyed, and officials are still searching for about 15 million pounds.

The meat was recalled on Sunday by a slaughterhouse in Chino, Calif., which had occasionally been allowing cows that could not walk to be butchered. Those animals, called downer cows, are banned from the human food supply because of increased risk of disease, including mad cow disease.

Most of the potentially tainted meat, about 93 million pounds, went to wholesalers who are assumed to have sold it to grocers and food processors. The Agriculture Department is contacting commercial customers of the meatpacker, the Westland/Hallmark Meat Company, to determine where the beef went and to try to recover as much as possible.

Despite demands from consumer groups, agriculture officials have refused to release the names of retail outlets that received the meat. The department says such information is proprietary, though it is pursuing a regulation that would allow retailers’ names to be publicized in future recalls.

The agency shut down Westland/Hallmark after the Humane Society of the United States released an undercover video on Jan. 31 that showed workers kicking and spraying water at cows and lifting them with forklifts.

The San Bernardino County district attorney has filed charges against two slaughterhouse workers for animal abuse. To date, there have been no reports of illness from the meat under recall order, and agriculture officials maintain that the risk is low.