How to stop the bite of horn flies

120,000 bites per day. During peak horn fly season, that can be a cow’s reality. But, there are simple things you can do to stop the bite at profit.

How to stop the bite of horn flies

During the peak fly season, as many as 4,000 horn flies can call a cow’s hide home. Each fly takes up to 30 blood meals per day. If you do the math, that adds up to 120,000 bites per cow.

These bites don’t just irritate your cows. They have a significant impact on profit. Production losses for the U.S. cattle industry are estimated at over $1 billion annually.1

High horn fly populations can cause:

  • blood loss

  • increased cattle stress or annoyance

  • use of energy to combat flies

  • altered grazing patterns

  • cattle grouping

  • decreased milk production

  • reduced calf weaning weights

Luckily, there are many ways to manage horn flies. One of the best ways is to break the horn fly life cycle in a cow’s manure. 

From mineral to manure 

So, how do you stop horn flies with manure?

Provide a mineral supplement containing an Insect Growth Regulator (IGR). An IGR passes through the cow and into her manure, where horn flies lay their eggs. IGR prevents pupae from developing into biting adult flies.

If you’re feeding mineral anyway, using a mineral with IGR can provide convenient horn fly control. While other fly control methods can require cattle handling, stress and additional labor, a mineral supplement with IGR can be consumed by the animal at its leisure. Fly control will be spread through the animal’s manure as it grazes.

Consistency is another benefit since cattle regularly consume mineral.

Follow the 30/30 rule

Start offering fly control mineral 30 days before the last frost in spring, before fly emergence.

This 30-day window at the beginning of spring is critical because temperatures can fluctuate to levels that cause flies to emerge. You want to have fly control in the manure when these flies arrive. If you miss this window, use other fly control methods to combat existing adult horn flies.

And, don’t forget to finish strong in the fall. Continue feeding mineral 30 days after the first fall frost.

Horn flies overwinter in the pupal stage, which can jump-start adult populations in the spring. By using mineral with IGR longer into the fall, you’ll decrease the opportunity for flies to overwinter and reduce your potential for large fly populations the following spring.

Choose your mineral

There are a variety of mineral supplements with IGR. So, how do you choose?

Rain can quite literally wash your mineral investment down the drain, or turn your mineral into a brick-type substance which cattle often refuse to eat. Select a mineral that can stand up to the unpredictable weather. Look for a weatherized mineral with large particle size and adequate water and wind resistance.

Remember, a mineral with IGR will only work if cattle are consuming it. If the mineral has been turned into a hard block or is blowing away with the wind, then your investment is a loss. A weatherized mineral can help safeguard your mineral investment and keep fly populations at bay.

Try fly control mineral today through the Purina® Feed Greatness™ Challenge, or learn more about fly control mineral at

1 USDA Report

About the Author(s)

Industry Voice by Purina Animal Nutrition


At Purina, we measure greatness by the animals we feed. It’s what drives our research to maximize the potential of every animal year in and year out. Because if there’s greatness on the inside, it shows on the outside.

Our expertise is backed by:

• 90 years of research in animal nutrition

• 24,000 animal nutrition studies

• 90+ nutrition scientists, Ph.D. and veterinarians

• 125 patents approved

• 235 nutritional solutions for 24 species

No other company matches our legacy and commitment to animal nutrition research.

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