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As we move into early summer, cattle producers may be noticing increased numbers of flies on their cattle. Horn flies are very common on beef cattle in Montana and annual losses in production and control costs exceed $780 million in the U.S. alone. When horn flies are abundant, cattle experience pain and annoyance from fly bites, which interfere with normal activities such as grazing and resting. Cattle infested with horn flies may exhibit decreased milk production, reduced weight gain, and poor feed efficiency.

Horn flies are external blood feeders and will bite an animal 20 to 30 time...