Police say they have broken up a theft ring that allegedly dealt in more than $11,000 worth of cow gallstones stolen since July at a meat packing plant. The gallstones, which are considered in the Orient an aphrodisiac, are the most expensive part of a cow, selling for more than $600 an ounce. Mike Sherman, president of the Cornhusker Packing Co., said Wednesday that the company sells the gallstones to a Japanese export firm. In a two-month period earlier this year the company sold 19 ounces for $13,000, Sherman said. Police on Wednesday charged four Omaha men with receiving stolen property valued at more than $1,000. A fifth Omaha man was charged Tuesday with theft by taking property valued at $300 to $1,000. Sgt. Charles Prokupek said four of the men are employees of Cornhusker Packing. The fifth is a local representative of Hyclone Laboratories, an Ogden, Utah, company that buys fetal calf blood from the packing plant, Sherman said. Sherman said the gallstones usually are collected by employees who work on the plant's kill floor and are supposed to be turned in at the office. The gallstones _ ranging in size from the tip of a pencil to an egg _ are sold to Japanese Export Co. of Minneapolis, he said.