The government prepared to suspend cattle shipments from Fukushima amid a growing tally of cows that fed on rice straw containing high levels of radioactive cesium. The development underscores the widespread and still-unfolding impact of the nuclear crisis at the Fukushima Dai-ichi power plant.

The straw was harvested from rice paddies in the prefecture after the March 11 earthquake and tsunami damaged cooling systems and triggered the release of radiation from the plant. The region's agricultural sector was among the hardest-hit as radiation seeped into water, affecting spinach and other leafy vegetables.

Distributors nationwide bought meat from the exposed cows, and some has already reached consumers.

Major supermarket chain operator Aeon Co. says more than 703 pounds (319 kilograms) of that meat ended up at 14 of its outlets in Tokyo and nearby prefectures. Between late April and mid-June, customers at those stores bought beef that came from a farm in Asakawa, Fukushima where cattle ate radiation-trained straw, according to the company.

Aeon says it will protect consumers by strengthening its radiation testing systems for beef.

Senior Vice Health Minister Kohei Otsuka said Sunday that the government may consider expanding the expected cattle restriction beyond Fukushima.

“We may need to increase our response by checking the distribution of contaminated straw,” he said on a national television talk show.

His comments came a day after Fukushima's government said 84 head of cattle shipped from five farms had been fed contaminated straw.

It also released results of tests conducted on remaining straw, which revealed cesium levels as high as 500,000 becquerels per kilogram at one farm in Koriyama City. That translates to roughly 378 times the legal limit.

The new revelation brings the number of exposed cows so far to 143, according to Kyodo News agency calculations.

The issue first gained attention on July 8, when the Tokyo Metropolitan Government said it had detected radiation in beef originating from a farm in Minami Soma, located about 16 miles (25 kilometers) north of the crippled nuclear plant. Its sample indicated 2,300 becquerels per kilogram.

Affected cattle growers have said they were unaware that the national government had issued a warning on March 19 that feed stored outdoors should not be given to their animals. A Fukushima government official acknowledged that the prefecture did not adequately pass along the instruction to farmers.

Local and national government officials say they are working to trace the location of the suspected meat and will improve safety checks.