story David J. Boxler
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July 5, 2013
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Tips from UNL specialists: Controlling flies on pastured cattle

There are three fly species in Nebraska that economically impact pastured cattle: horn fly, face fly and stable fly, and control of these flies can be economically beneficial to cow-calf and stocker/yearling operations.

Horn Fly

The horn fly is one on the most important blood feeding pests of pastured cattle in the United States.

Losses in the U.S. have been estimated at about $800 million annually.

When horn fly numbers are high, cattle experience annoyance and blood loss. 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 pounds 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.

CONTROL — 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 percent to 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.

Face Flies

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.

CONTROL — 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 pinkeye 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. ❖


David J. Boxler is an extension educator for the University of Nebraska-Lincoln’s West Central Research and Extension Center in North Platte, Neb.

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The Fence Post Updated Oct 16, 2013 03:02PM Published Aug 5, 2013 01:55PM Copyright 2013 The Fence Post. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.