Q. What is the economic impact of horn flies on cattle production?
A. Horn flies are the number-one economic ectoparasite1 in North American cattle production, causing an estimated $1 billion loss annually. Compare this to the estimated loss due to bovine respiratory disease at $600 million or pinkeye at $100 million.

Q. How can I tell if I have a horn fly problem?
A. Horn flies are an ectoparasite of cattle and tend to stay on the backs and sides of animals throughout the day. Despite their name, horn flies do not congregate on the horn and head area. Horn flies are about half the size of the common house fly and lay eggs exclusively in fresh manure.

Q. How do horn flies affect cattle?
A. Horn flies cause cattle stress. Under stress, cattle will not feed as freely and may move to areas in or near water to escape fly pressure. A moderate horn fly population (500 per animal) will suck 7 cc of blood per day. Typical weight loss is estimated at 15 to 50 pounds per yearling. Also, a 10- to 15-pound weaning weight advantage results when good horn fly control is used.2

Q. What’s the best way to control horn flies?
A. Most horn fly control strategies require you to either gather cattle on a regular basis for treatment or replenish the various systems that dispense products for horn fly control (dust bags, backrubbers, etc.). While these methods are labor-intensive, an insect growth regulator (IGR) allows you to provide horn fly control right in your feed or minerals, letting cattle do the work.

Q. How do I know if my horn fly problem is worth treating?
A. University research indicates the economic threshold for horn flies is 200 per animal and, for dairy cattle, may be as low as 50 flies per animal.

Q. How do I calculate the cost of horn fly control?
A. The cost per animal will vary and can be measured on a return-on-investment (ROI) basis. For ear tags, you should also consider the cost of labor to determine the real cost per animal. 

1 Byford, R.L., Craig, M.E., Crosby, B.L., A Review of Ectoparasites and Their Effect on Cattle Production, J. Anim. Sci., 1992, 70:597-602.
2 Source: NebGuide, University of Nebraska Cooperative Extension Service.