Production Losses Associated with Flies

Flies annoy and irritate animals, transmit disease, reduce weight gains, and reduce milk production.

Horn flies can cause significant economic losses. They are biting, blood-sucking flies that feed 20 to 40 times per day, reducing milk production up to 20% and decreasing gains in growing cattle by 0.25 to 0.5 lb per head daily (USDA) if not controlled. Five hundred horn flies per animal will consume about 1 gallon of blood in a 30-day period.
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Stable flies can do as much if not more damage than horn flies. Stable flies feed with a piercing-sucking mouth. According to the University of Illinois, as few as 40 flies per animal can cause significant reduction in milk production. The USDA estimates milk production losses at up to 20% without good control.

Economic losses may occur when the fly population reaches 100 flies per animal. Over 200 flies per animal can cause significant economic losses. A good fly control program using an oral larvacide, backrubber at peak season, and time-released insecticide provides a favorable cost:benefit ratio.

Fly Control Management Recommendations

  • Practice good sanitation management.

  • Keep fly populations under control. Elimination is not the goal. Treat fly levels over 100 flies per animal. Keep the population below 200 flies per animal.

  • Use periodic treatments, rotating insecticide methods (sprays, dust, backrubbers).

  • Use an oral larvicide with periodic treatments for cattle on pasture.

  • To reduce over-winter fly phase, treat late in the fly season.

  • If using insecticide tags as part of the pest control program, follow usage recommendations throughout the season.

  • Use a pyrethrin for quick kill and reduction of all fly populations.

Resistance Issues

  • Insecticide ear tags were introduced in the early 1980s. Originally, they were very effective; however, favorable results lasted only a few years. Due to management practices and other factors, resistance to the insecticides used in ear tags quickly developed.

  • Resistance to man-made pesticide compounds (pyrethroids, organophosphates, etc.) can occur in a specific fly population.

  • Resistance can be widespread, but not uniform.

  • The flies' resistance mechanisms are different for different compounds.

  • Insecticide resistance is often perceived rather than actual due to inadequate application, poor timing, inadequate total control program, and/or sudden resurgence of flies if conditions are ideal.



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ADM Animal Nutrition, a division of Archer Daniels Midland Company