Controlling Flies on Pastured Cattle
There are three fly species in Nebraska that economically impact pastured cattle: horn fly, face fly and stable fly. Control of these flies can be economically beneficial to cow-calf and stocker/yearling operations.
When horn fly numbers are high, cattle experience annoyance and blood loss (see image at right, click on image for larger view). The result may be decreased milk production, reduced weight gains, changes in grazing patterns and bunching of animals. Significant reduction in calf weaning weights is well documented. Nebraska studies demonstrated calf weaning weights were 10 to 20 pound higher when horn flies were controlled on cows. In addition, horn flies have been implicated in the spread of mastitis.
The economic injury level (EIL) for horn flies is 200 per animal and population numbers of several thousand of flies can often be observed during the summer.
The horn fly is a blood feeding fly that is located on the shoulders, back and belly region of cattle, they take some 20 to 30 blood meals per day and the only time they leave an animal is when the female deposits eggs in fresh cow manure. The complete life cycle, egg to adult, can be completed in 10 to 20 days during warm conditions. In Nebraska, where we typically have several generations during the summer, horn fly populations can reach very high levels.
Horn fly control for pastured cattle involves different insecticide use strategies. These include dust bags, back-rubbers (oilers), animal sprays, oral larvicides (feed-additives), pour-ons, and insecticide impregnated ear tags.
Force-use, self-treatment devices, such as dust bags and back-rubbers (oilers), provide effective and economical fly control. Studies have shown that horn fly control is 25-50 percent less using free-choice methods.
Animal sprays can be an effective way on reducing horn fly numbers. Drawbacks with animal sprays are increased cattle handling, cost, and added stress to the cattle during the fly-season.
Oral larvicides and insect growth regulators (IGR) prevent horn fly larvae from developing into adults. These can be delivered to cattle as loose mineral, mineral blocks or tubs. To be effective cattle must consume a specified amount of product per day. Proximity to untreated cattle and inadequate consumption by cattle are two factors that can contribute to poor fly control.
Pour-on insecticides are ready-to-use formulations applied along the back line of cattle. Although pour-ons will control flies for short periods, the stress in cattle in using this method may offset the benefits of the fly control.
Insecticide impregnated ear tags contain one or more insecticides embedded in a plastic matrix. To achieve the maximum performance from an insecticide ear tag, two tags per animal are required, and delaying ear tagging until June 1st will provide a producer with the greatest degree of horn fly control. A livestock producer in Nebraska can expect 12 to 14 weeks of horn fly control if the aforementioned methods are utilized.
The face fly is a robust fly that superficially resembles the house fly. It is a nonbiting fly that feeds on animal secretions, nectar, and dung liquids. Adult female face flies typically cluster around the animals' eyes, mouth, and muzzle, causing extreme annoyance.
In addition to being very annoying to cattle, face flies vector Moraxella bovis, the principal causal agent of bovine pinkeye or infectious bovine keratoconjunctivitis. Pinkeye is a highly contagious inflammation of the cornea and conjunctiva of cattle. If coupled with the infectious bovine rhinotracheitis (IBR) virus, M. bovis can cause a much more severe inflammatory condition.
Controlling face fly numbers is a key to reducing pink-eye problems. Because face flies are on animals for only short time periods they are difficult to control.
Fly control methods described in the discussion of the horn fly can be used against the face fly. Insecticide ear tags, if used according to label recommendations, provide a higher degree of face fly control. Both cows and calves must be treated if control is to be achieved.
In respect to pink-eye vaccines, commercial and autogenous pinkeye vaccines are available. Please check with a local veterinarian about the use of these products in a specific geographical area.
Stable Flies on Pastured Cattle
Stable flies are pests of cattle on pastures in the Midwest. Stable flies mainly feed on the legs of cattle. To avoid being bitten, animals stomp their feet and switch their tails. Other avoidance behaviors include standing in water, lying with legs tucked underneath and bunching at the corners of pastures.
The effect of stable flies on weight gain performance of pastured cattle is similar to that of livestock in confined operations. Research conducted at the University of Nebraska, West Central Research & Extension Center recorded a reduction in average daily gain of 0.44 lb per head per day in 84-day trials compared to cattle that received an insecticide application. The economic threshold of five flies per leg is easily exceeded in Nebraska pasture conditions.
The female fly deposits eggs in spoiled or fermenting organic matter mixed with animal manure, moisture and dirt. The most common breeding sites are in feedlots or dairy lots, usually around feed bunks, along the edges of feeding aprons, under fences and along stacks of hay, alfalfa and straw. Grass clippings and poorly managed compost piles also may be stable fly breeding areas. Winter hay feeding sites where hay rings are used can often be a source for stable fly development through the summer if the proper amount of moisture is present.
The only adult management option available for control of stable flies on range cattle is use of animal sprays. These products can be applied using a low pressure sprayer or can be applied with a mist blower sprayer. Weekly applications of these products will be required to achieve reduction in fly numbers. Sanitation or clean-up of wasted feed at winter feeding sites may reduce localized fly development. If sanitation is not possible these sites may be treated with a larvicide (Neporex®). However, the implementation of either procdure may not reduce the economic impact of stable fly feeding.
For more information, please see the recording of the May 2nd webinar "Fly Control for Cattle on Range and Pasture" or the Market Journal May 17th segment on Fly Control.
For fly control recommendations, please go to the UNL Department of Entomology’s “2013 Nebraska Pasture Fly Control Product Recommendations” page.
David J Boxler, Extension Educator
West Central Research & Extension Center
University of Nebraska–Lincoln, North Platte, NE
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