China's Ministry of Commerce said Wednesday it will extend an anti-dumping investigation into U.S. exports of a certain kind of animal feed for another six months.

The probe over the U.S.-produced distiller's dried grains with or without solubles will last until June 28, 2012, because the case is "special and complicated," the ministry said in a statement.

The ministry decided to start the investigation on Dec. 28, 2010, in line with the country's anti-dumping rules, the statement said.