SHREWSBURY — Charles River Laboratories International Inc., which conducts research for drug developers, will suspend operations at its Shrewsbury facility and lay off 300 workers by mid-2010 because of weak demand for the company's preclinical services, Charles River reported yesterday. The company, based in Wilmington, said it expects to retain about 30 workers who will handle ongoing operations at the plant or take jobs at other Charles River sites. Charles River said it expects the move will cut operating costs by about $20 million this year. The company has no plans at this time to dispose of the plant, said...