Omnicom Group Inc., New York, hired William M. Mercer Consulting to help it decide whether to merge 43 defined contribution plans run by some of its numerous subsidiaries, said Leslie Chiocco, director of retirement benefits at Omnicom. The 43 plans hold a total of $250 million in defined contribution assets, she said. Omnicom is a holding company that owns several advertising and marketing companies, which are decentralized. The largest subsidiary is DDB Worldwide, which has a $50 million defined contribution plan. In addition, Omnicom sponsors a defined contribution profit-sharing plan, which totals $670 million in assets. Some employees participate in both plans. Omnicom considered merging plans seven years ago when there were only eight and three years ago when there were 23, but the company had never hired a consultant to help it review all the plans, Ms. Chiocco said. If the firm merges the plans and issues RFPs for managers, Mercer will do the screening.