Know your Fly Control Options for Dairy Cows.

 By Jaclyn Krymowski.

 Flies are a pain to control - especially amid the busy, hot summers when there are so many other things to do. It doesn’t matter if cattle are kept indoors, in small or large groups or out on pasture, if the flies can find them, they will.

The weight of the burden varies depending on the time of year and environmental conditions. In wet years, populations of external and internal parasites increase. Even the way neighboring farms are managed can influence the regional population.

There is no question that flies, like all parasites, have a financial impact. Multiple, low-impact efforts can go a long way to stave off the worst of infestations. However, it must be an ongoing, fluid plan, sometimes called an integrated pest management (IPM) plan.

Common fly types
There are various species of flies that target cattle. Each has its own behaviors and lifecycle. Some feed on blood. Others feed on normal secretions from the eyes and nose. And some lay eggs that develop into grubs under the skin.

Several of these species also spread disease between individual animals and across different herds. Most of them prey on bodily secretions like manure, tears and blood. Common examples include horn and face flies, deer and horse flies, stable flies, heel flies and house flies.

Horn flies are small and tend to bother cattle on their backs, sides or bellies. They mate and deposit eggs in manure. For dairies and heifer raisers, managing manure can go a long way in limiting the breeding grounds for such flies.

Another pest with a hefty economic impact for the cattle industry is the face fly.

Face flies (similar to, but not the same as house flies) are non-biting flies that feed on animal secretions, nectar and dung liquids, so they are usually on an animal’s eyes, mouth and muzzle. In his bulletin, Controlling Flies on Pastured Cattle, University of Nebraska extension specialist Dave Boxler cautions that the face fly can cause damage to eye tissues, and increase susceptibility to eye pathogens and pinkeye while they are feeding.

Pinkeye is one of the costliest flies due to its pathogenicity, expense and difficulty to treat.

For feedlots, dairies and pasture cattle, stable flies are serious pests as they are a blood feeder. They are usually found feeding on the front legs. Boxler notes that for these flies, grass clippings and poorly managed compost piles are great breeding sites. Ensuring that compost piles are managed and away from cattle can help reduce the impact of this fly.

Economic impact
As with all parasites, the economic impact of flies is difficult to pinpoint. Essentially, they cost dollars on two fronts - lack of productivity due to irritation and damage due to disease treatment.

“An integrated pest management (IPM) plan should be utilized to sustainably reduce fly populations below the economic threshold. Integrated pest management combines cultural, biological, and chemical means for fly mitigation,” writes former extension educator Nathan Briggs in his Penn State bulletin How to Manage Fly Pests in the Cattle Herd.

These will also be referred to in the control methods.  Better understanding the major methods can decrease economic impact.

Horn and face flies are the two major species of flies that cause the most problems for producers. Horn flies specifically are widely believed to be the most economically damaging of the fly pests, particularly for pastured cattle, as they can transmit blood-borne diseases, according to University of Wisconsin-Madison extension educator Ashley Olson.

Economic losses associated with horn flies, Boxler notes, are due to the impact they have on the decreased grazing efficacy, reduced weight gains, and diminished milk production in dams.

“Studies conducted in the U.S. and Canada have shown that horn flies can cause weight gain/loss in cattle, and calf weaning weights can be negatively impacted from four to 15 percent,” he writes.

Control methods
For horn flies, there are multiple control options ranging from backrubbers or dust bags to insecticidal ear tags, pour-ons and sprayers. Boxler notes that typically sprays and pour-on products are only effective for seven to 21 days.

Dairies also have the added burden of ensuring all chemical products they use are safe for lactating animals. Even topical and externally applied products must be vigorously vetted.

Feed additives (many of which are dairy safe) are a popular choice for low-input, and effective fly control. These largely work by disrupting the lifecycle of the parasites via the cow’s digestive tract and manure, significantly curbing population growth. These work on a wide variety of fly species.

Face flies tend to be more difficult to control as they spend time around the animal’s face, eyes and ears. For these flies, daily application is often the most effective. This includes dust bags, oilers, sprays (more effective for cattle on pasture), or an insecticide-impregnated ear tag or strip.   

Effective face fly control may require more than one method of treatment, according to Patrick Wagner in his South Dakota State University bulletin Fly Control Considerations for Cattle on Pasture. This is in contrast to horn flies because both cows and heifers must be treated in order to reduce face fly populations.

The best protection all season is to use a combination of sprays or oilers early in the season followed by ear tags, Olson says. Dust bags and oilers should be located where cattle will frequent them, such as holding pens or other high-traffic areas.

Another pest management method is cultural, meaning an alteration of the environment the pest would normally thrive in. This includes sanitation and management of barn, pasture, and surrounding facilities. Regularly taking care of manure and having proper storage for manure, compost piles and feed ingredients can help reduce the pest population.

A biological method would be to implement predatory insects to kill and consume the flies, eggs, and/or larvae such as releasing wasps weekly or biweekly.

The third and final method is chemical control. As previously discussed, this includes ear tags, feed additives, larvicides, baits, rubs, bags, residual premises, whole animal (pour-on), space sprays, and building treatments. Insecticides are beneficial and useful but should be used with caution as they can potentially harm beneficial insects.

Though it can be tricky to manage flies, it is well worth your time and effort. The most successful approaches are broader than a single, one-time pass. They involve learning about the flies themselves and applying control methods in a timely and strategic manner.