For the past few years, we have been using fly powder on the cattle to control the flies. Anytime we work the cattle, we apply a dusting from the nose to the tail along the back. As we have a nice alleyway and headgate, it is fairly easy to run six to eight cows in and sprinkle them with powder. The calves are treated in the same fashion. As we have many friendly cows, it is easy to do repeat dustings as needed.
Using fly powder has made a marked difference in the number of flies on the cattle. There are other ways to reduce the fly population as well, especially if the cattle are not close to handling facilities.