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West: Nutrition: Managing the annoyance of pasture flies

Ryan D. Rhoades for Progressive Cattleman Published on 24 June 2019

The grazing season on Western rangelands is in full swing, and the presence of flies (i.e., horn, face and stable) on cattle can have negative impacts on health and performance. Summer represents peak fly populations, and for much of the West, moisture has been good, which intensifies this management challenge.

Annoyance and blood loss from flies biting cattle can result in reduced milk production, weaning weights and gain, and cause cattle to change grazing behavior and bunch. Improving fly control could increase both financial and resource efficiency on grazing operations. Since managing pasture flies is so critical to our bottom line, here are a couple of considerations.

1. Consider taking inventory

Producers are often aware of flies, but fail to consider population thresholds of economic importance. Fly infestation populations not controlled can reach several thousand per animal. Experience indicates that bunching and other negative effects start when populations exceed a much lower threshold (i.e., approximately 150 horn flies and five stable flies). Consider routinely assessing cattle for fly populations between 8 and 11 a.m. At this time, most flies can be found on the topline or side of the animal. An afternoon measure will be less accurate since most flies will reside on the belly region.

2. Consider treatment costs and delivery systems

Several insecticide systems for fly control are currently available. Older methods such as dust bags and oilers are inexpensive but require forced use for maximum effectiveness. Pour-ons have immediate impact, but only provide seven to 21 days of control. Mist blowers and sprayers are highly effective on all fly types, but initial costs are high and necessitate weekly application.

Newer delivery systems (i.e., CO2-powered gun and/or capsule) are the most convenient method, but require multiple applications, and the cost per treatment is higher. Eartags and tag strips that gradually release low levels of insecticide are a convenient and cost-effective option. However, eartag rotation (i.e., insecticide classes) is recommended to manage fly resistance to control products.

3. Consider preventative measures

Sanitation and cleanup of wasted feed at winter feeding sites can help prevent localized fly development. Feed-through products kill developing larvae in the manure, but steady consumption is necessary. Always remember to read the label and follow proper treatment procedures. The need for a detailed monitoring and control program is the common link among each consideration.  end mark

Ryan D. Rhoades
  • Ryan D. Rhoades

  • Assistant Professor
  • Beef Extension Specialist - Colorado State University
  • Email Ryan D. Rhoades

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