A day after the Food and Drug Administration (FDA) announced that H5N1 avian flu fragments have been found in retail milk samples, the US Department of Agriculture (USDA) today announced that lactating dairy cows must be tested before interstate transport.

The movement of dairy cows, some of which aren’t showing disease symptoms, from already affected states such as Texas has been a source of H5N1 spread to dairy herds in states such as Idaho and Michigan. Also, the identification of virus fragments in finished milk suggests that the virus may be more widespread in dairy cows than currently known.