Officials suspect that the hay was stored outside and became tainted with rainwater, which can carry radioactive elements in the atmosphere as it falls. Though hay is not usually fed to cattle here, a feed-supply shortage after the March 11 quake and tsunami forced some farms to substitute it for other food.

Some farmers in the region say that they welcome tougher checks, and that cattle can still be shipped from Fukushima if precautions are taken against radiation exposure.

Yuta Furuyama, who has 233 cattle in Minamisoma, is certain his herd is clean. His cattle are kept indoors, and their feed is stored in thick plastic bags, out of the rain. He said he was careful to not even bring tools that he has used outside into the cowshed, for fear of contaminating his herd, which he is eager to have tested for radiation so that his cattle can be safely sold later this year.

“I hope they will finally step up the checks,” he said. “If the government had given proper advice and done proper tests in the first place, things wouldn’t have gotten out of hand.”

Japanese government officials insist that even at levels above government limits, radioactive cesium will not have an immediate effect on health. Longer-term effects are less known, however. Many experts say that prolonged exposure to radiation can lead to a higher incidence of cancers like leukemia.

“If you eat it every day, it might be a problem,” Goshi Hosono, the minister in charge of the nuclear issue, said last week. “But if you eat just a little, there would be no big effect on your health.”

Experts, however, disagree on what the effects may be of exposure to radiation above the limits but at low doses.