Japan has lifted a ban on beef imports from two U.S. meat packers after reviewing the companies'' steps to improve safety measures following unauthorized shipments that contained parts believed to pose a risk of mad cow disease, as reported ty the Associated Press. The Agriculture Ministry said it resumed imports from the Pennsylvania plant ran by the Smithfield Beef Group, and the National Beef California LP, effective immediately. Japan halted shipments from the two plants earlier this year after finding parts banned under a bilateral trade pact. Shipments from the Smithfield plant were suspended in January after meat from a 21-month old cow was found. Japan halted imports from the National Beef plant in April, when its shipment contained spinal cord. The ministry said its on-site inspection in August at 10 authorized U.S. meat packing factories, including the two that had been suspended, confirmed that they had taken measures to prevent banned parts from slipping into boxes for shipment to Japan. Under terms of the nations'' pact, U.S. beef shipped to Japan must come only from cattle age 20 months and younger, which are thought to pose less of a risk of the disease. U.S. exporters must also remove spinal columns, brain tissue and other materials from shipments bound for Japan.