Ruth Correll: My feed-through fly control isn’t working

Ruth Correll • Updated Jul 17, 2018 at 4:45 PM

Feed-through fly control has, without doubt, become one of the most popular types of feed additives utilized in pasture-based beef production systems. Feed-through fly control can be a valuable component of a comprehensive fly control program, however its misuse often results in lost opportunities and limited return on investment. 

It is important to understand how it should be used to maximize its efficiency. One thing that all feed-through fly control products have in common is that they have no direct effect on the animal – rather they have their effect in the animal’s manure. While the animal consumes the additives, they move through its digestive tract relatively unchanged and are deposited in the animal’s manure. This is where they wage their war against flies. Although they are delivered to the manure in a similar manner, their differences lie in mode of action. As such, these additives generally fall into one of two categories, insect growth regulators or larvicides.

Insect growth regulators are compounds that typically interfere with the progression of normal fly development. In other words, these products work through inhibiting or delaying the progression of fly larvae from one stage of development to the next. Because of this, IGR products are generally species specific and thus target only a single fly species. Most commonly available IGR products are only effective on horn flies.

In contrast to IGR, larvicides elicit a structural change in the fly that leads to death before it is able to reproduce. In other words, these products prevent flies from breeding. Because of this mode of action, larvicides generally are not species specific and thus target more than one species of fly. As a result, larvicides target not only horn flies, but also face flies and stable flies. 

Because of their differences, it is important to make sure that you are using the correct product to achieve your goals for fly control and meet your expectations. For example, occasional situations arise where an IGR is used, but the producer does not believe it is working because he or she still sees flies. Since that product is intended to control horn flies, do not expect it to reduce pressure from face flies or stable flies. Similarly, larvicides may affect insects other than flies that also reproduce in manure.

Getting ahead of the game is important, which means beginning to feed these products one month or more before fly season. This could be one of the major explanations for why the product you are using does not seem to be working now.  You had a generation or two of flies before beginning the use of these products. If you don’t begin feeding either of these products until flies are already a problem, you’re going to limit their efficacy. Similarly, product efficacy is dependent upon feeding these products throughout the duration of the fly season. As a result, it is necessary to extend feeding through the second major killing frost.

Because the products work in a dose-dependent manner, it is imperative that cattle consume the necessary amount of product. This means that cattle must consume the amount of feed required to deliver the necessary level of IGR or larvicide, and they must do so on a consistent basis. Take steps to ensure that these products are consumed in a manner that will allow consistent delivery of the necessary amount of drug to manure.

Another factor that limits the efficacy is their use as the sole means of fly control. While they may still provide some benefit when used alone, feed-through pesticides are not a “silver bullet,” and perform best when used as a component of a comprehensive fly control program. Thus, it is recommended that they be used in combination with other methods of control, such as insecticide-impregnated ear tags, administration of topical insecticides such as sprays, pour-ons, rubs, etc. and proper manure management. 

Proper manure management is the area that is most commonly overlooked. In scenarios without manure management the efficacy of these products is substantially limited, as flies will almost always have access to manure that was not exposed to the product. Take the necessary steps to ensure that “old manure” doesn’t limit product efficacy. 

Due to regulatory jurisdiction, most mineral supplements or other feed products that contain a feed-through pesticide are also medicated with another drug. Currently, the most commonly paired drug is an ionophore such as Bovatec or Rumensin.

Some products can be purchased as “add-packs” and incorporated into a free-choice mineral supplement or other feed on-farm, however, doing so may increase costs considerably when compared to purchasing a pre-manufactured supplement or feed that already contains the product. It is important that you put pencil to paper to determine the most economical option. 

Bottom line, feed through fly control works if used properly. Proper steps must be used and it works much better if combined with other fly control methods. For additional information, consult with your local veterinarian or your local Extension office.

For more information, contact the UT-TSU Extension Office in Wilson County at 615-444-9584. You can also find us on Facebook or visit extension.tennessee.edu/wilson. Ruth Correll, UT Extension-TSU Cooperative Extension agent in Wilson County, may be reached at 615-444-9584 or acorrell@utk.edu.


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