Beef Pasture

Costing the North American cattle industry over $1 billion annually, horn flies are a major concern for pastured beef cattle. Despite the fact that these pests cause weight loss and are vectors for beef heifer mastitis, many ranchers do not take action when it comes to controlling them.

Conventional fly control methods such as ear tags and pour-ons reduce populations through direct toxicity. Horn flies in many areas have developed resistance to these labor-intensive methods as a result of overuse. Alternative methods include feed throughs like Altosid® IGR. Requiring little to no labor, this option controls flies by interrupting their life cycle during the larval stage. The active ingredient in Altosid® IGR has not had any cases of resistance since its introduction to the market place in 1975. Further, because Altosid® IGR is formulated for beef cattle on pasture, it specifically targets horn flies without causing damage to beneficial parasites and other fly species. A recent study confirmed that stocker cattle treated with Altosid® IGR, a feed-through horn fly control solution, experienced a 15.8% increase in average daily gain compared to cattle who went untreated.

Next Steps

Understanding the Problem

Horn flies are the most common fly species on pasture. And while these bloodsucking parasites may be small, they make for big problems. Each fly can take up to 40 blood meals a day, causing stress in cattle. Consequently, cattle expend extra energy trying to dislodge flies and normal feeding patterns are disrupted. Along with blood loss, this leads to significant reductions in weight gains.

Another major problem is that horn flies are a vector for mastitis and the resulting blind quarters. They carry bacteria such as Staph. Aureus, which is the primary cause of mastitis in cattle. When flies bite udders, this bacteria can enter into teats and move up the quarter, where it destroys milk producing tissues.

Mastitis and blind quarters can cause up to a 20% drop in milk production – and milk yield accounts for more than 60% of the variation in calf weaning weight. Overall, a bad horn-fly infestation can result in a loss of up to 50 pounds per yearling. Economically speaking, this adds up to an average of $45 per head.

The best way to identify a horn-fly infestation is to look for groups of small flies congregating on specific parts of cattle. Observations taken between 9AM and 1PM are most accurate, as this is when horn flies are located in visible areas like the back and shoulders. It is important to note that horn flies stay on the cattle day and night – the only time they leave is to lay their eggs in fresh cow manure.

To better understand stable flies and the damage they can cause on cattle, equine and swine operations, click on our Stable Fly icon.

Horn Fly

  • Takes up to 40 blood meals with piercing mouthparts
  • Congregates on the backs of cattle, leaving only to lay eggs in fresh manure
  • Painful bites can interfere with feed efficiency and weight gain of cattle
Next Steps

Fly Management Through IPM

Effective control of costly fly populations among beef cattle requires a complete integrated pest management (IPM) program. In addition to feed-through products, an IPM program incorporates several routine practices and control methods that keep fly populations in check.

Building an IPM program can be broken down into three phases; planning, implementation of biorational and cultural controls, and evaluation.

Click on the pie chart below to learn more.

Pie Chart
To plan the best integrated pest management (IPM) program for a beef pasture, read our planning tips for fly control for cattle by clicking here. The final step to a success integrate pest management (IPM) program on a beef pasture is evaluations. Get best practices by clicking here. Get best practices on implementing an integrated pest management (IPM) program on a beef pasture to control flies on cattle by clicking on this icon.
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How Feed-Through Products Work

Conventional pesticides attack the nervous systems of flies. A feed through, such as Altosid® IGR, works by interrupting the fly’s life cycle rather than through direct toxicity.

Altosid® IGR is ingested with the cattle’s mineral or feed. As they graze, cattle disperse the IGR via their manure, where female flies lay their eggs. The eggs hatch into larvae, and after three to five days they molt into pupae. At this point, however, the active ingredient in Altosid® IGR disrupts the development of the fly by naturally mimicking the biochemicals that are responsible for insect development. The fly life cycle is effectively ended here.

For best results, Altosid® IGR should be added to your feed supplement 30 days before fly emergence (typically when average daily temperatures reach 65 degrees) and continued throughout the season until 30 days after the first frost. To learn more about the 30/30 program, download our 30/30 White Paper.

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Altosid® IGR Formulations

Selecting the right formulation of feed through for specific operations is necessary for an effective integrated pest management program. It is dependent on multiple factors, including the size of the operation, the animals’ weights and the intensity of the fly problem.

Altosid® IGR can be mixed at the feed dealer, custom blended or sold as a manufacturing-use product with varying levels of active ingredient. Altosid® IGR representatives can help feed dealers and producers decide which of the following formulations is right for them.

To learn more about these formulations, visit

Altosid® IGR Formulations:

  • Altosid® IGR Blocks and Tubs – Ready-to use formulations with varying levels of active ingredients, available in mineral or protein tubs or blocks.
  • Altosid® IGR Granules – Compact formulations for mixing, available with .02% and .01% active ingredient levels.
  • Altosid® IGR Premix – Feed concentrate for mixing on farm, in free-choice-fed minerals and mixed-ration feeds. Available with a .4% active ingredient level.
  • Altosid® IGR 1% Liquid – Liquid formulation for custom blending with a 1% active ingredient level.
  • Altosid® IGR 2% – A manufactured-use product meant for mixing into EPA-registered products such as Altosid® IGR 0.02% or 0.01%.
Next Steps

Become Certified

This is an opportunity to become certified in Centralized Fly Control. By no means an official designation, Centralized Fly Control Certification will improve your feed-through knowledge so you can provide your customers with accurate product knowledge and expertise in how to control flies across a variety of livestock markets.

Become Certified