Workers at one of the nation’s largest meatpacking plants have agreed to return to work and halt a three-week strike after plant owner JBS USA agreed to resume negotiations, labor union representatives announced Saturday. The strike by thousands of workers at the Swift Beef Co. plant in Greeley, Colorado, began on March 16 in coordination with the United Food and Commercial Workers Local 7 union in a bid for higher wages and better health care. The strike came as U.S. cattle numbers hit a 75-