Controlling flies on cattle | Ag Proud (2024)

Nuisance flies have a major impact on cattle and other livestock species. One of the most dominant impacts of flies to the cattle industry is the financial impact. Herds of cattle that are severely impacted by flies will have decreased grazing efficiency because of fly annoyance. In growing cattle in feedlot settings, decreased weight gains have been observed due to high fly populations causing poor living conditions. In cattle heavily impacted by flies, blood loss, skin irritation and pink eye all negatively impact the industry financially.

The three most common fly species to impact cattle are horn flies, face flies and stable flies.

• The horn fly is small, 3/16-inch in length and usually found on the backs, sides and poll area of cattle. They acquire more than 30 blood meals per day and lay eggs in fresh cattle manure. A horn fly will complete its life cycle in 10-20 days depending on the weather, primarily the heat and moisture, around the egg.
• The face fly is slightly larger and darker than a house fly. It is a nonbiting fly that feeds on animal secretions, nectar and dung liquids. Face flies will cluster around an animal’s eyes, mouth and muzzle, and it can cause extreme annoyance. It will also feed on blood and other secretions around wounds. They are present throughout the summer, but populations peak in late July and early August as temperatures increase. They are most numerous along waterways, areas with abundant rainfall, shaded vegetation and irrigated pasture.
• The stable fly is a blood feeder mainly feeding on the front legs of cattle, causing their bites to be very painful. They will stay on the animal long enough to complete a blood meal, which causes the cattle to react by stomping their legs, bunching at pasture corners and standing in water to avoid being bitten.

Heel flies can also be rather bothersome to cattle. They are about the size of a honeybee. They produce eggs laid on the cattle in the spring that then hatch, and the larvae tunnel through the skin. Their activity can cause cattle to scare and run.

Flies develop quickly in warm and wet weather. The wetter the weather the worse the fly populations will become because female flies need moist organic material to lay their eggs in. To help combat growing populations, you can make some management changes to reduce the egg-laying environment. The first step is sanitation. Spilled hay and feed, especially wet feeds, should be cleaned up to disrupt the fly life cycle. Waste should be composted, compacted or spread in a thin layer on crop production sites.

Another way to combat fly populations is with the use of insecticides. Insecticides are chemical controls that are either naturally derived or synthesized that provide effective insect control for livestock and horses. Benefits of insecticides include effective and quick control that improves animals’ well-being and productivity. When using insecticides on livestock, you must always carefully read and follow label instructions. Some insecticides can be harmful to humans and other animals and should be handled with care to prevent accidental poisoning. These products also have a withdrawal time, depending on their formulation. In that case, you must record and follow the withdrawal time before harvesting the animal.

There are many different formulations for insecticides. Some common application methods for fly control are animal and residual sprays. These can be used to control flies by being sprayed either directly onto the animal or in the surrounding area like a loafing shed or barn. Residual sprays are useful in areas where animals commonly bed down as they can provide control for several weeks. Another popular application method is pour-on. These are ready-to-use formulations applied in measured doses to animals based on bodyweight. To ensure adequate control and to reduce incidence of resistance, accurate weights should be taken on the animals prior to application.

Other forms of insecticide application that can be useful with a larger group of cattle are self-treatment devices like dust bags, oilers and insecticide eartags. Dust bags and the like will need to be reloaded according to label directions and should be taken down during rain events. Baits can be useful in areas with high populations to help provide a reduction in population. Insecticide eartags are useful but should be rotated yearly to help reduce resistance to the active ingredients. Oral larvicides are also useful as they can be consumed by the animals via mineral blocks or loose minerals and reduce the need to work the cattle to apply the insecticide.

If horn flies are one of the species negatively impacting your herd, the best methods for control are those that can be applied directly to the animal or consumed by them. This would include back rubbers, dust bags, insecticide eartags, pour-ons and animal sprays. The best way to impact horn fly populations is to treat the animal that the fly is feeding on. In addition to these direct applications, larvicides can also help prevent the fly larvae from developing into adults.

Face flies can be treated with daily insecticide application achieved via back rubbers and eartags help to control these flies. Their populations can be harder to control because of the amount of time they spend away from the animal and because they do not consume the animal’s blood, like the other species. To have adequate control, all animals on the premises must be treated for face flies.

Stable flies can be a major nuisance to cattle. For the best control of stable flies, cattle may need weekly application of insecticide. Because of their need to rest on the animal, they can be well controlled by practicing good sanitation practices and cleaning up spilled feed and manure. Cleaning up wet feed reduces egg-laying ground for the flies, thereby reducing their populations.

Heel flies are best controlled during the larval stage or grub. Treatment can be achieved with many products used for intestinal worms that will also control the larval stage of cattle grubs. For cattle being scared by heel flies, you can use contact sprays for some short-term relief.

One of the challenges with fly control is knowing when to start utilizing insecticides. The economic injury level is when it becomes cost-effective to begin treatment of the animals at the point impact of the fly population will negatively impact the animal’s individual production. The economic threshold for horn flies, which land on the back and sides of animals, is 200 flies per animal. The threshold for stable flies is five flies per leg. If gone untreated, the flies' impact can cause blood loss, decreased grazing efficiency, reduced weight gains and diminished milk production.

In summary, the best way to treat flies is to first understand what fly you are treating for. Remember: Face flies are found on the face, stable flies are found on front legs, and horn flies are found on the back and sides. Be aware that insecticides can develop resistance over time, so you should rotate products annually. For all fly species, good sanitation practices will help control egg-laying habitat and reduce fly populations.

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