All these cows were fed with radioactive rice hay. The rice growers sold the rice hay, and the cattle farmers fed the rice hay, because there was no government regulation on radiation concerning the storage, sale, and use of the rice hay.
The authorities will probably have to find out where else the radioactive rice hay has been sold. The rice hay in Koriyama City in Fukushima tested 500,000 becquerels/kg of radioactive cesium, enough to contaminate non-contaminated cows elsewhere in Japan.
From Fukushima Minyu (7/16/2011):
浅川町の肉用牛農家が餌として与えた稲わらから高濃度の放射性セシウムが検出された問題で、浅川町の肉用牛農家には白河市の稲作農家でつくる生産者グループを通じて稲わらが販売され、浅川町の農家、白河市の生産者グループ双方とも、稲わらの管理や販売に関する国や県からの指示がなかったと話していることが１５日分かった。
Regarding the high level of radioactive cesium detected from the rice hay that was fed to the meat cows at a cattle farm in Asakawa-machi, it was revealed on July 15 that the rice producer group in Shirakawa City (which is located adjacent to Asakawa-machi) sold the rice hay to the cattle farm. Both the cattle farm in Asakawa-machi and the rice producer group in Shirakawa City say there was no instruction from the national government or the Fukushima prefectural government regarding the storage and the sale of the rice hay.
牛の餌に関する国、県の放射線検査は、東京電力福島第１原発事故後に成長した牧草を対象に行われてきたが、稲わらは検査の対象外だった。南相馬市の肉用牛から高濃度のセシウムが検出された際も餌の稲わらが汚染源と判明、検査態勢の甘さが浮き彫りとなった。
The radiation testing of cattle feed has been done only on grass feed that has grown after the Fukushima I Nuclear Power Plant accident, but the rice hay was never considered for testing. It turned out that the high level of cesium detected in the meat cows from Minami-Soma City was also due to the rice hay fed to the cows. The government's lax testing procedure is now coming to light.
I do have sympathy for cattle farmers and their suppliers in Tohoku, but when I read the news I am disappointed that they simply followed the guidance (in this case the lack thereof) from the government and not used their common sense that the hay sitting outside or rolled after the Fukushima accident might be contaminated with radioactive materials and it would be better to treat it the same way as the grass feed, which was regulated. Instead, they decided to use the rice hay, or sell it, because the government didn't have any rule on it.
I also understand the farmers' situation that there was nothing else to feed their cows, since the supply of cattle feed got interrupted by the earthquake/tsunami and then by the Fukushima accident. So they were trying to find a way to feed their cows, and they found the rice hay, which was outside the regulation. So they fed the cows with the rice hay and hoped for the best.
If the grass feed that was growing outside since the accident was contaminated, it doesn't take much imagination to figure out that the same radioactive materials might be also falling on the rice hay.
You may ask, "What should they have done, then? Let the cows starve?"
I don't know. But they should have raised bloody hell demanding the government, the prefecture, TEPCO, anyone at all anywhere, provide them with clean feed. Instead, they persevered, quietly figured out the way to save the cows. A very Japanese way.
However, there's another "baseless rumor" floating around: That the radioactive rice hay is a red herring, and the real culprit is the well water that the cows had been drinking. But the government, both national and prefectural, would dare not say that and dare not test it because they are planning on forcing people back into these areas with the declaration of the "step 1" of TEPCO's "roadmap" having been successfully completed.