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UW Extension Releases Report on Horn Fly Management for Beef Cattle

December 16, 2022
close up of flies on a cow
Counting the number of horn flies on a single cow can help estimate the extent of infestation in the entire herd. UW Extension recently released a report that presents the latest research and management options for cattle ranchers faced with horn fly infestations. (UW Extension Photo)

A recent report published by University of Wyoming Extension presents the latest research and management options for cattle ranchers faced with horn fly infestations.

Titled “Horn Fly Management for Wyoming Beef Cattle,” the new publication examines the pest’s life cycle; potential impacts on herd health; and season- and altitude-related trends.

“Horn flies are the most damaging external parasite of cattle in the U.S.,” says Derek Scasta, rangeland management specialist for UW Extension, who co-wrote the report.

The report’s writers explain how to estimate levels of infestation and provide management recommendations, urging producers to consider economic factors and the variety of treatment options before acting.

“Wyoming cattle producers should consider the complexity of the situation to determine if and when treatment is appropriate,” Scasta says.

Counting individual flies might seem like an impossible (or impossibly tedious) task, but regular monitoring is the key to making informed management decisions. The report’s writers offer guidelines on how to estimate flies per cow on a handful of animals to extrapolate the level of infestation in the entire herd.

These estimates then can be used to determine whether control measures are needed. For horn flies on beef cattle, the economic threshold is estimated to be about 200 flies per cow. When the number of flies on an animal exceeds this threshold, the value of loss becomes larger than the cost of control.

If treatment is deemed necessary, the writers recommend integrating multiple control strategies. Depending on the situation, control options might include animal rotation and habitat disruption; chemical treatments, such as backrubbers, ear tags and sprays; and breed selection.

Some elevations and animals may be more susceptible to high infestation levels, researchers note. UW studies suggest that, as elevation increases, horn fly numbers may drop.

Certain breeds of cattle -- as well as individuals within those types -- may exhibit greater resistance to infestations, meaning that intentional selection may offer a viable management strategy over time.

To learn more about horn fly management, go here for a downloadable copy of the report.

About University of Wyoming Extension 

Since 1914, UW Extension has provided lifelong learning opportunities to Wyoming citizens across the state. With roots in agricultural education, UW Extension supports rural communities facing contemporary challenges and changes. UW Extension brings the university’s resources to each of the state’s 23 counties and the Wind River Indian Reservation. To learn more about UW Extension, call (307) 766-5124 or visit

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