The United States Department of Agriculture will begin mandatory testing of US milk supplies for bird flu. The Friday announcement was a break from the previously voluntary testing program for the bird flu virus known as H5N1.

This strain of bird flu was first found in US dairy cattle in March, according to the USDA. Secretary of Agriculture Tom Vilsack said in a statement that the testing program “will give farmers and farmworkers better confidence in the safety of their animals and ability to protect themselves, and it will put us on a path to quickly controlling and stopping the virus’ spread nationwide.”