Restaurant chain Yoshinoya D&C Co. launched a five-day campaign Thursday to promote sales of pork-on-rice dishes, which it introduced after running out of beef last month due to a ban on imported U.S. beef.

Yoshinoya President Shuji Abe joined cooks at an outlet in Tokyo's Yurakucho area, where he served as manager early in his career, to launch the "butadon" drive, in which a standard-size bowl has been cut to 250 yen from 320 yen.

Clad in the company's orange uniform, Abe used a ladle to top bowls of rice with cooked pork, handing them to other staffers before they were passed on to customers.

The pork dish was introduced as a replacement for "gyudon," which is rice topped with beef.

Yoshinoya and other gyudon chains had to stop serving beef dishes last month, with Japan having banned beef from the United States, which suffered its first case of mad cow disease late last year.

The firms relied almost entirely on U.S. beef.