There are three fly species that economically impact pastured cattle; Horn Fly, Face Fly, and Stable Fly
Horn Fly Economic Impact
The Horn Fly is one of the most significant blood-feeding parasites of pastured cattle in the United States. Losses have been estimated at $1 billion annually. Feeding can cause irritation, blood loss, decreased grazing efficiency, reduced weight gains, and a decline in milk production. Furthermore, Horn Flies have been implicated in the spread of summer mastitis. Studies in Nebraska have demonstrated calf weaning weights were 10-20 pounds higher when Horn Flies are controlled on the mother cows. Yearling cattle weight gain can also be impacted by up to 18%. The economic injury level (EIL) for Horn Flies equals 200 flies per animal. Horn Flies usually remain on the cattle but they can travel several miles looking for an animal to feed upon. They spend most of their time on the back, head, and shoulders of its’ host . When it’s hot or rainy, they may relocate to the belly of the animal. They take around 20-30 blood meals per day, only leaving the animal for 10 minutes or so to lay their eggs in cow manure. Adults emerge in mid-March, with populations peaking in late May or early June as well as late August or early September as weather conditions moderate.
Force-use self-treatment devices, like dust bags and back-rubbers (oilers), provide effective and economical fly control. However, if used in a free-choice arrangement expect 25-50% less Horn Fly control. Animal sprays and mist-blower sprayers can also be effective. Mist-blower sprayers are taken to the pastures and applied to the animals, reducing animal stress. . Pour-ons are ready to use products applied to the back midline of cattle. Nebraska studies indicate pour-ons will keep Horn Fly numbers below the EIL for up to three weeks. Insecticide impregnated ear tags containing one or more insecticides in its’ matrix are another great control method. Oral larvicides and insect growth regulators prevent fly larvae from fully developing in the manure. To be effective, cattle must consume a specific amount of product each day. Proximity to untreated cattle and inadequate consumption are two factors that can contribute to poor fly control.
The Face Fly is a robust fly that resembles the House Fly, only it slightly larger and darker in color. It is a nonbiting fly that feeds on animal secretions, nectar, and dung liquids. The female Face Fly feeding activity can cause damage to eye tissues and increase susceptibility to eye pathogens. The fly can also be a vector/carrier for Moraxella bovis, the causal agent of bovine pinkeye. Controlling Face Flies and pinkeye vaccinations are essential in reducing the spread of pinkeye. Due to the fact that Face Flies remain on animals for short time periods, they are difficult to control. A larger percent of their time is spent off host. Fly control methods described in the discussion of the Horn Fly can be used against the Face Fly. Insecticide ear tags appear to provide a higher degree of Face Fly control.
Stable Flies are a serious pest of pastured cattle. They are a blood-feeding fly that usually feed on the legs and belly of the animal. Their bite is very painful causing cattle to react by stomping their legs, crowd in corners of pastures, and stand in water to avoid being bitten. Stable Flies cause similar weight losses to both pastured and confined cattle. The University of Nebraska researched and recorded a reduction in average daily gain of .44 pounds per day in animals that received no insecticide treatment compared to animals that received treatment. Populations of five flies per leg are often exceeded in Nebraska pastures. However, we do know that Stable Flies can travel ten miles or more. The female fly deposits her 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 the feed bunks, edges of feeding aprons, under fences, and along stacks of hay, alfalfa, or straw. Grass clippings and poorly managed compost piles also supply the Stable Fly with viable breeding areas. The only management option available for control on range cattle is the use of animal sprays. Products such as coumaphos (Co-Ral), permethrin and natural permethrin (under many brand names, and Phosmet (Prolate) are available for use. Clean-up of wasted feed at winter feeding sites may prevent localized fly development but may not reduce economic impact of the Stable Fly feeding.