Four of those herds are in Colorado, where the first infection was detected in the northeastern part of the state in April.
The USDA and the Colorado Department of Agriculture are asking farmers and ranchers to watch for signs of infection.
The first case in a cow was discovered in Texas after a farm cat died and was found infected with the flu.
Canadians and Americans are now testing milk for traces of the virus.
Meanwhile, three flocks have the virus and have been euthanized.
