Iowa Sens. Chuck Grassley and Joni Ernst last week asked Agriculture Committee Chairman Pat Roberts to hold a hearing on the federal government’s response to the rapid spread of bird flu in Iowa’s egg-laying and turkey operations.

As of June 3, the outbreak had affected more than 29 million commercial poultry in Iowa, including 24 million layers, 3.8 million pullets and 1.2 million turkeys, according to the Iowa Department of Agriculture and...