More than 4 million chickens in Iowa will have to be killed after a case of the highly pathogenic bird flu was detected at a large egg farm. The outbreak announced Tuesday is the latest flock to be slaughtered in a yearslong outbreak that is increasingly affecting dairy cattle as well. Nearly 1.4 million chickens also were killed at an egg farm in Minnesota after bird flu was detected May 21. Overall, USDA data shows 92.34 million birds have been killed since 2022. Also in May, officials say a second dairy farmworker was diagnosed with bird flu. It has been confirmed on dairy cattle farms in nine states.