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Minamisoma, Japan – Even after explosions rocked the Fukushima Daiichi nuclear power plant, Kuniaki Sato, who raises cattle here about 20 miles from the crippled complex, said he had received no clear warning from the government about the possible dangers of radiation to his herd.

So six weeks after the accident, on April 23, he shipped 12 of his prized cattle from his farm to market.

Now Japanese agricultural officials say meat from more than 500 cattle that were likely to have been contaminated with radioactive cesium has made its way to supermarkets and restaurants across Japan in recent weeks. Officials say the cattle ate hay that had been stored outside and exposed to radiation.

“I was a little worried, but we had to sell when we could,” said Mr. Sato, whose cattle were not fed hay and so were unlikely to have been contaminated.

When a precautionary order to halt all farm shipments was lifted soon after the accident, area farmers took it as a go-ahead sign, he said. “We all resumed shipments,” he said. “Of course we did.”