Dairy cows can no longer cross state lines without being tested for bird flu, federal authorities said Wednesday, the day after the FDA announced that inactive viral fragments had been found in pasteurized milk. The US Department of Agriculture said dairy cows need to test negative for influenza A viruses before they can be transported across state lines, the New York Times reports. The tests will protect livestock and help officials “better understand this disease,” said USDA official Mike Watson. The agency says the outbreak has spread to 33 herds in eight states. Dozens of people are being …