Nearly a third of Kentucky’s labor force has filed for unemployment insurance, the largest share of any U.S. state, partly reflecting officials’ encouragement to do so and an early move to expand workers’ eligibility. Those factors, combined with a high concentration of factories and the postponement of the Kentucky Derby, caused about 671,000 state residents to seek jobless benefits in the seven weeks ended May 2, according to the U.S. Labor Department. That is equivalent to about 32% of the February workforce and well above…