Yum Brands is fighting to restore its battered image in China, vowing to tighten monitoring of its mainland supply chain after a chicken safety scare dealt a significant blow to its sales in the country.

Earlier this month, Yum Brands, owner of the KFC fast-food chain, forecast a drop in 2013 earnings due to the fallout from food safety concerns surrounding its Chinese business. Claims in December that the group’s suppliers had injected growth hormones and antiviral drugs into chicken beyond food safety limits hit confidence in the brand, which had previously traded on its reputation for food that is safer than domestic fast-food competitors.

Yesterday, Yum, the biggest foreign restaurateur in China by sales, went on the offensive to try to limit damage from the scandal, announcing that it would strengthen oversight of its suppliers and expand drug testing. It said more than 1,000 small producers used by 25 poultry suppliers to the company had been dropped.