FEED BEEF - Using Altosid® IGR for Fly Control

   Using Altosid® IGR for Fly Control

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A convenient way to control horn flies in beef and dairy cattle is to give them minerals or other feed containing Altosid® IGR. Altosid is an insect growth regulator (IGR) that passes through the animal and into the manure, where horn flies lay their eggs. It breaks the horn fly life cycle by preventing pupae from developing into biting adult flies.

The active ingredient in Altosid is methoprene, an analog of the horn fly’s own juvenile growth regulant.

    Why Just Horn Flies?

Horn flies are the pests that cost producers the most money. Animal irritation and stress, reduced rate of gain, reduced feed efficiency, and spread of disease add up to lost production that can significantly reduce profit. Other flies may be visible but do not have near the economic impact of horn flies.

Horn flies stay very close to the animal virtually all their lives, biting, sucking blood, and laying eggs in fresh manure. Other flies (face flies, house flies, and stable flies) may spend significant time away from the animal and may lay eggs in other places, making fly control for these species extremely difficult.

Left untreated, a few horn flies can quickly explode to a population of 1,000 to 4,000 flies or more per animal. Scientists estimate that an economical, effective program keeps the fly population below 200 per animal. Occasionally, adult flies migrate from other herds. Feed-throughs, like Altosid, do not kill adult flies. However, Altosid does prevent flies from successfully multiplying, breaking their life cycle.

Used as directed, Altosid is not harmful to birds, fish, reptiles, mammals, or beneficial insects. In addition, there is widespread horn fly resistance to organophosphates and pyrethroids. Yet, even after years of use, there is no known resistance to Altosid.

     Feeding Altosid

Altosid can be fed to cattle, including lactating dairy cattle, using Altosid IGR 0.4% Premix mixed with feed. For beef cattle on pasture, Altosid can be conveniently and economically delivered with one of these MFA Gold Star minerals for as little as 3 to 4 cents more per head per day:

  • 5% Maximum Pasture Gainer with Altosid Fescue Equalizer with Altosid
  • Season-Long Fly Control

Horn flies emerge in the spring, when average daily temperatures reach 65°F for a period of at least two weeks.

    For effective horn fly control with Altosid:

  • Begin feeding Gold Star mineral with Altosid before flies appear.

  • Put out a 5 to 7 day supply. Protect from rain.  

  • Use one feeder per 15 to 20 animals.  

  • Place the feeders near watering or resting areas.  

  • Check mineral consumption for a few days. Increase or decreaase the number of feeders or move them, if necessary, to achieve targeted daily consumption.

In most years, Altosid alone provides excellent season-long control when used as directed. If fly populations exceed acceptable levels (likely due to migration from untreated neighboring herds), use an approved adulticide to knock back the fly population.

For more information, contact Janice Spears at

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