Cattle producers recognize that fly control is a profitable summer management practice. Depending on a number of characteristics of the farm/ranch operation, several methods of fly control are available. More and more producers now prefer the convenience of a feed-through product.

Currently there are a number of free-choice feed-through products in the marketplace, but in the majority of these products only two active ingredients are represented: an organophosphate and methoprene (IGR Minerals® products). Producers that recognize the value of summer mineral supplementation and like the convenience of a free-choice product may question which active ingredient is the better buy. Several aspects of each product should be investigated.

In that each of the active ingredients has been cleared for use against horn flies in a feed-through product by the Environmental Protection Agency, effectiveness is not an issue. Once either product is deposited in the cattle manure, it breaks the horn fly life cycle, interrupts development, and thus stops population growth of horn flies. Uniform, Regular Mineral Intake Is A Must With A Feed-Through Product.

For feed-through products to be effective:

1. The expected level of intake must be achieved. If the active ingredient is not present in treated manure at the expected level, it will not work.

2. Regular mineral intake is also important. In training Sales Representatives about IGR service, Alliance Nutrition scientists have continually made the point that cattle, which have a break in their consumption of our product for three days or more, will produce untreated manure. Increased fly populations will follow this break in consumption by about two weeks.

3. Continual mineral intake must be achieved during the hot, dry part of the summer as well as late spring or early fall.

These factors help explain the importance of starting a herd of cattle on  mineral before introducing IGR and the value of uniform intake throughout the season. Established intake levels help ensure adequate and regular intake of the active ingredient. Producers considering the potential use of products containing the other active ingredient should also make sure mineral intake will be at expected and regular levels continually throughout the horn fly season.

There Are Differences Between The Two Active Ingredients.

The 2000 Feed Additive Compendium from the Food and Drug Administration shows specifically what the differences are between the two active ingredients. It shows what information must appear on any product label and the approved level of feeding of the additive. The printed statements for each active ingredient are as follows:

Methoprene

Caution: Keep out of reach of children. Discard empty container according to local regulations. Never reuse empty container.

Approved dosage for cattle is 22.7–45.4 mg/100 lb of body weight/month.

Organophosphate Feed Additive

Caution: Keep out of reach of children. Harmful if swallowed. Avoid contact with skin and eyes. Avoid breathing dust. Wash thoroughly with soap and water after handling and before eating and smoking. If in eyes, wash eyes with plenty of water. If irritation persists, get medical attention. Wear long sleeved shirt and pants, chemical resistant gloves and shoes and socks for protection when handling. This chemical may cause skin sensitization reactions in certain individuals. This product is toxic to fish. Do not contaminate water when disposing of equipment wash water.

Approved dosage for cattle (beef and dairy) is 2100 mg/100 lb of body weight/month (0.07 grams/cwt./day).

The organophosphate does have a label for the control of fecal flies in the manure of treated cattle. It prevents development of face flies, horn flies, house flies and stable flies in the manure of treated cattle. IGR is only labeled to prevent the breeding of horn flies in the manure of treated cattle only. Consider the facts that house and stable flies are only a problem in areas where manure accumulates. As a result, they are primarily pests of confined rather than pastured cattle. They also breed in materials other than cattle manure. Therefore, just treating cattle manure may not control these two species of flies. Face flies are strong fliers that tend to travel from one group of cattle to another. Therefore, treating cattle via manure may not ensure freedom from face flies as they may migrate to neighboring herds.

What About Resistance Development?

Chemical resistance would develop most rapidly when adult flies are being treated rather than during immature stages. Under these methods of control, adult flies that tolerate a chemical pass their resistance to their offspring. This explains recent failures of a number of ear tags which contain pyrethroids as their active ingredient. In an effort to prolong the use and effectiveness of these tags, manufacturers use different classes of insecticides in addition to pyrethroids in their tags including carbamates and organophosphate. In some cases, this has resulted in low level cross resistance to that class of compounds as well.

In addition, in the late 1970s organophosphates were used exclusively in ear tags. Failures of these products were noted in Florida and Georgia in the early 1980s. These failures were attributed to resistance development of the horn fly population. While a feed-through product containing organophosphate does not treat adult flies, some resistance to organophosphates may exist due to previous treatments of the fly population with this class of compounds. When cattle were fed organophosphates over an 18 month period, researchers from Georgia demonstrated development of resistance to organophosphates.

In conclusion, methoprene used in IGR has only been used as a feed-through to treat immature flies. No incidence of resistance has been reported by customers since it was introduced to the market in 1977.

Methoprene is a very safe and effective product in the control of horn flies. Just as importantly, its carrier, the Alliance Nutrition mineral package, helps ensure the required intake and provides excellent supplemental nutrition to pastured cattle.