They were not fed with radioactive rice hey.
Some people in Japan suspected from the beginning when the meat cows from Fukushima were found with radioactive cesium that it was not just from the feed but from air and water. They were dismissed by the government officials who insisted the problem was just the radioactive rice hay.
Both the national government and the Fukushima prefectural government encouraged the cattle farmers in the evacuation zones in Fukushima to sell their cows and pigs to cattle farmers outside Fukushima, and many farmers bought them. Now they are being raised all over Japan.
From Asahi Shinbun (5:00AM JST 8/20/2011):
島根県は１９日、福島県内の牛を５～６月に購入した農家１５戸のうち２戸の堆肥（たいひ）から放射性セシウムを検出、１戸は国の暫定基準値（１キロあたり４００ベクレル）を超えていたと発表した。これらの牛と排泄（はいせつ）物について農林水産省は、福島県への調査などを踏まえ、牛の移動と出荷を認める通知を島根県に出していた。
Shimane Prefecture announced on August 19 that radioactive cesium was detected at two cattle farms out of 15 that had purchased meat cows from Fukushima Prefecture in May and June. At one of the farms, the level exceeded the provisional safety limit (400 becquerels/kg). The Ministry of Agriculture, Forestry and Fisheries had issued a notice earlier to Shimane Prefecture that it was free to move and ship meat cows, based on the survey results from Fukushima Prefecture.
島根県内では５月以降、一部の肥育施設で宮城県産の汚染稲わらが納入され、堆肥の一部から放射性セシウムが検出されたが、これらの牛とは別という。
In Shimane, radioactive rice hay from Miyagi Prefecture was used at some cattle farms, and some manure has been found with radioactive cesium. The cows, whose manure was found to be radioactive this time, are not at these farms.
島根県によると、１５戸は福島県の臨時家畜市場から福島第一原発周辺の農家が肥育していた牛を含む計７７頭を購入した。農林水産省は７月２１日、牛と排泄物を農場内に保管するよう通知。このうち６４頭について今月１１日、汚染わらは与えられていなかったとして県に出荷を認める通知をしていたという。
According to Shimane Prefecture, the 15 cattle farms purchased the total 77 cows at the temporary cattle market in Fukushima, which included cows from the farms near Fukushima I Nuclear Power Plant. The Ministry of Agriculture, Forestry and Fisheries notified on July 21 that the cows and the manures should be kept on the farms. However, on August 11, the ministry notified the Shimane prefectural government that 64 cows could be shipped because they were not fed with radioactive rice hay.
島根県の独自検査で、６４頭中、２頭を購入した１戸から２７００ベクレル、３頭を購入した別の農家で１００ベクレルを検出した。県は今後、７７頭のふんと尿を採取し検査するという。
However, Shimane Prefecture did its own survey and found out that the manure at one cattle farm that had purchased 2 Fukushima cows was tested for 2,700 becquerels/kg of radioactive cesium, and the one at another cattle farm that had purchased 3 cows was tested for 100 becquerels/kg. The prefecture will test all 77 cows for radioactive materials in their excrement and urine.