It is the first time that cows infected with the virus have been identified.
The cows appear to have been infected by wild birds, and dead birds were reported on some farms, the agency said.
The Texas Animal Health Commission confirmed that the influenza subtype known as H5N1 has been identified and said that the virus resembled the version that has been spreading in birds across the nation.
Pasteurisation should inactivate the flu virus, experts said, and officials stressed that the milk supply was safe.
