Generally, this includes promoting breeding in the cow herd, growth and weight gain in calves, and health in all animals.

Unfortunately, there are numerous factors that take away from the positive inputs provided. The list is substantial and can all but drain any profits that might normally be produced. Things like internal parasites, stress (environmental, handling, etc.) and disease all act as a drain on the animal, reducing their ability to perform as necessary.

One of the most significant factors affecting cattle production is also one of the most common: flies. Flies are a constant irritant and performance drain on cattle, whether they are on pasture or in a drylot. They can take nutrients from the animal by constant bloodsucking, produce exceptional levels of stress due to the constant irritation and transmit a variety of diseases, which obviously contributes to additional productive and economic losses.

Measuring the effects that fly infestations may have can be very difficult. Various studies have estimated that to the cattle industry, the annual expense can exceed $1.5 billion annually. Horn flies alone are estimated to cost cattle producers well over $850 million.

What does this mean to the individual producer? With a fairly heavy infestation of a combination of these pests, probably a $30-to-$50 per head per year loss can be sustained. Again, these costs are difficult to quantify given farm-to-farm variabilities.


One particular area to consider is the nutritional “cost.” For instance, horn flies are aggressive bloodsuckers, and each individual fly can consume 20 to 30 “meals” of the animal’s blood per day. With a typical uncontrolled or poorly controlled fly population per animal of several hundred flies, this can result in a pint of blood taken from the animal every day.

This means that important nutrients consumed by grazing and feed intake are required, not only for the animal’s maintenance requirements and the protein, energy, minerals and vitamins needed for normal performance – a significant portion of these nutrients must be directed to blood synthesis. Specifically, this can be appreciable in terms of the effect on dietary protein requirements.

Normal populations of horn flies usually average several hundred, but as few as 50 flies per animal can be enough to negatively impact performance. Thousands can occur, and populations this high can consume enough of the cattle’s blood to cause anemia.

Horn flies occur mostly on the cow and usually only by proximity on calves. Studies have shown that untreated brood cows can result in a 12 percent decrease in the average daily growth rate of nursing calves. Additionally, growth rates of yearling stocker cattle and lactation rates of dairy cows may decrease by around 16 percent.

Metabolic and behavioral responses indicate that horn flies increase the amount of energy spent by cattle when defending themselves, leaving less dietary energy for growth.

Given the level of stress a heavy fly population creates, this has additional effects on the animal’s ability to efficiently use nutrients it consumes. This stress also goes on to depress immunity in the animal, thus making it more susceptible to a variety of diseases, not only those the flies may carry or promote such as anaplasmosis and pinkeye.

face fliesFemale face fly feeding causes damage to eye tissues and increases susceptibility to eye pathogens (particularly Moraxella bovis, the causal agent of pinkeye). 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. Horn flies have also been implicated in the spread of mastitis.

Understanding the problem

Several species of flies can contribute to the issues. These include but are not limited to:

Horn flies

Horn fly infestations cause irritation, blood loss, decreased grazing efficacy, reduced weight gain in calves and diminished milk production in mother cows. Horn flies are small in size, approximately 3/16-inch in length and typically populate the backs, sides, belly and poll areas.

As mentioned before, together, male and female flies can acquire more than 30 blood meals per day. After mating, the female fly will leave the animal to deposit eggs in fresh cattle manure. Eggs hatch within one week, and larvae feed and mature in the manure, pupating in the soil beneath the manure pat.

Newly emerged horn flies can travel several miles searching for a host. The entire life cycle can be completed in 10 to 20 days depending upon weather conditions.

Face flies

Face fly adults closely resemble houseflies – except they are slightly larger and darker. The face fly is a non-biting/sucking fly that feeds on animal secretions and fecal liquids. The adult female face flies cluster around an animal’s eyes, mouth and muzzle, causing extreme irritation. Face flies will also feed on blood and other secretions around wounds caused by mechanical damage, injury or feeding sites from horn or stable flies.

Face flies are present throughout the summer, and populations usually peak in late July and August. They are most numerous along ponds, waterways, areas with abundant rainfall, areas with trees and shaded vegetation, and on irrigated pastures.

Stable flies

Stable flies are serious pests of feedlots, dairies and pasture cattle. Like horn flies, stable flies are blood feeders, persistently feeding on the front legs of cattle. Their bites are very painful; cattle will often react by stomping their legs, bunching at pasture corners or standing in water to avoid being bitten. The female stable fly deposits eggs in spoiled or fermenting organic matter mixed with animal manure, soil and moisture.

The most common sites are in feedlots or dairy lots, usually around feedbunks, along the edges of feeding areas, under fences and along stacks of hay, alfalfa and straw. Winter hay feeding sites where hay rings are used can often be a source for larval development through the summer if adequate moisture is available.

The life cycle of the stable fly can take 14 to 24 days depending on location and weather conditions. It is also known that stable flies can move 10 miles or more.


The most effective way to control fly populations is to take an integrated pest management approach to both the adults and larvae. The horn fly’s ability to thrive allows for large densities in a small amount of time, and just treating for the adults will not decrease the infestation. The best approach is to use several methods at once, focusing on population and source reduction.

Fortunately, a variety of control methods are available to manage fly numbers. Unfortunately, few of these are completely effective independently, so a combination must be used. Some of these include:

  • Backrubs and dust bags are an effective way to reduce horn fly numbers if cattle are forced to use them.

  • Insecticide-inclusive eartags (pyrethroids and organophosphates) are a convenient method of horn fly control. However, many horn fly populations exhibit some resistance to the pyrethroid class of insecticides. As such, it is recommended to alternate tag classes every year or two.

  • Animal sprays and pour-on products will provide seven to 21 days of control and will need to be re-applied throughout the fly season.

  • Feed-through or oral larvicides including Rabon (labeled for horn, face, houseflies and stable flies) and like Altosid (insect growth regulator, labeled for horn flies) can be used starting 30 days before flies typically emerge.


Managing fly populations in beef cattle herds is a critical management component in an effort to support and promote productivity and profitability. Understanding the effects, timing and life cycles along with nutritional drains, stress results and potential disease exposure illustrates the need for a sound, combination program of control system to reduce fly populations in the herd.  end mark

PHOTO 1: Horn flies are small in size and typically populate the backs, sides, belly and poll areas.

PHOTO 2: The face fly is a non-biting/sucking fly that feeds on animal secretions and fecal liquids. Photos provided by Stephen Blezinger.

Stephen Blezinger
  • Stephen Blezinger

  • Management and Nutritional Consultant
  • Reveille Livestock Concepts
  • Email Tim Clarks