FILE - Cows stand in the milking parlor of a dairy farm in New Vienna, Iowa, on Monday, July 24, 2023. The bird flu outbreak in U.S. dairy cows is prompting development of new, next-generation mRNA vaccines — akin to COVID-19 shots — that are being tested in both animals and people. In June 2024, the U.S. Agriculture Department is to begin testing a vaccine developed by University of Pennsylvania researchers by giving it to calves. (AP Photo/Charlie Neibergall, File)