A farm cooperative in Ombetsu, eastern Hokkaido, said Wednesday that a cow confirmed Monday to be infected with mad cow disease was fed the same milk substitute when a calf as were the three other cows infected with the disease in Japan.

The agricultural cooperative said all four cows in Japan so far confirmed as having bovine spongiform encephalopathy (BSE) had been fed milk substitute produced by Scientific Feed Laboratory Co. in Takasaki, Gunma Prefecture.

According to the cooperative, the farmer in Ombetsu started feeding the cow with the milk substitute in 1996 when it was a week old.