CHICAGO, Sept 8 (Reuters) - Poultry company Perdue Farms will buy natural meat maker Niman Ranch, which is Chipotle Mexican Grill's biggest pork supplier and a brand name on U.S. restaurant menus, the two companies said on Tuesday. Privately held Perdue expects to "soon" close a deal to buy Natural Food Holdings, which owns the Niman Ranch brand, from private equity firm LNK Partners, according to a statement. Terms were not disclosed. The deal marks the latest move by a big food company seeking to expand its presence in the fast-growing U.S. natural foods market. It risks displeasing some consumers, who are attracted to Niman Ranch's reputation for working with independent farmers and raising animals without antibiotics. Niman Ranch plans to continue producing animals in... More