The outlook for U.S. agricultural exports is growing brighter because of an improved trade agreement with Canada and Mexico, along with negotiations on bilateral trade deals with Japan and other key importers, the U.S. Department of Agriculture’s (USDA) top trade official said last week during a visit to Iowa.

“It feels good to be on offense,” Ted McKinney, USDA under secretary of agriculture for trade and foreign agricultural affairs, said after a meeting with Iowa agricultural leaders in Des Moines. “These really are positive developments for expanding export markets around the world.”

The proposed trade deal with Canada and Mexico, called the...