SEOUL/CHICAGO, Oct 10: South Korea has suspended some U.S. Beef imports after detecting the cattle feed additive zilpaterol in meat supplied by a unit of JBS USA Holdings Inc , raising concerns that the controversial animal growth enhancer may still be in the supply chain weeks after Merck & Co halted sales of Zilmax, the top-selling zilpaterol-based drug. The South Korean claim of zilpaterol-tainted beef is the first to come to light since Merck suspended sales of Zilmax on August 16 amidst concerns about its impact on the health of cattle. (agencies)