Yoshinoya D&C Co. became one of the first casualties in Japan of the mad cow disease case in the United States, announcing Tuesday it will stop serving its mainstay "gyudon" beef-over-rice at its outlets in early February if there is still an import ban on U.S. beef.

The company, which started business in 1899 and now runs some 980 outlets in Japan, had been importing up to 99 percent of its beef from the U.S. The ban forces the chain to discontinue its main, and effectively only, menu item for the first time in its history.

"This is the biggest crisis ever," said Yoshinoya President Shuji Abe, who was also working for the company when it filed for bankruptcy in 1980.