An executive of Perdue Farms, the nation’s fourth largest producer of chicken products, will head the Salisbury-based company as CEO starting this summer. The fourth-generation, family-owned poultry producer on Wednesday named Kevin McAdams, chief operating officer of Perdue Farms and president of Perdue Foods, as the next CEO. He will replace Randy Day, a 40-year Perdue veteran who will retire after having been CEO since 2017.