Current Progressive Cattle digital edition

Drop the flies before problems bite you

Drew Shain Published on 24 February 2013
Cows with their calves

Fly control minerals could be the answer to this costly insect issue

A heavy infestation of horn flies can consume up to a half-pound of blood per cow per day.

With stiff, needle-like mouths, the insects thrive on cattle, often taking 20 or more blood meals each day.

Though the mature insects are less than one-quarter inch in size, they can cause significant problems in herd productivity and health if not prevented in early spring.

When not prevented, one horn fly can lay up to 500 eggs in 10 to 20 days.

These fly groups can quickly overpopulate a pasture. In fact, industry estimates show that several thousand horn flies may be present on just one cow as spring turns into summer.

Horn flies can cause cows to devote considerable energy to replenishing consumed blood, warding off insects and searching for a reprieve.

In most cases, grazing patterns become off-balance, and energy available for lactation, maintenance and growth are minimized.

When looking at the numbers, it is clear that fly prevention is a critical part of a productive cattle herd. Studies show that yearling grazing heifers gain 15 to 50 pounds more when insect populations are managed.

Similarly, ongoing studies through the University of Nebraska – Lincoln demonstrate a 10-pound to 15-pound advantage in calf weaning weights from cows with managed fly populations.

To promote these perks and a positive grazing season, producers should evaluate insect prevention options in late winter.

Most successful fly control programs in the upper U.S. include prevention beginning at least 30 days prior to fly emergence. The process should then continue through 30 days after the area’s first kill frost.

Typically prevention is needed March through October, depending on the area’s climate. Warmer areas should consider a year-round fly control program.

If the early window is missed and adult flies begin the reproduction cycle, populations can grow quickly. Mature flies can often not be controlled without a spray or insecticide treatment, which can be costly and time-consuming. Moreover, spraying for flies cannot logistically be accomplished in most pasture settings.

For that reason, stopping flies before they start is ideal. This can be done by providing an insect growth regulator, such as Altosid IGR or Methoprene, through the herd’s mineral program.

By using Altosid in the mineral, the fly’s reproductive cycle is permanently delayed before reaching maturity.

Insect growth regulators are consumed by the cow through the mineral and passed directly into her manure. Horn flies lay eggs in fresh manure, where the insect growth regulator binds with the eggs and begins to work.

As the egg goes through its life cycle, the insect growth regulator keeps the fly in its pupae stage, keeping the fly from reaching maturity.

Because the fly never hatches into an adult, it spends its entire life in the manure pile, the reproduction process never occurs and the fly population is controlled.

Insect growth regulators through minerals are the only insect prevention option for grazing cattle that stops fly populations before they begin.

Other insecticide methods, including sprays, dust bags and fly tags, may work in conjunction with mineral fly control but may be more difficult to manage.

For instance, with dust bags, cows need to enter specific areas, and with fly tags research shows the probability of insect resistance building over time.

Horn flies are unable to build resistance to insect growth regulators because the flies never reach the reproduction stage.

Altosid is also formulated to only prevent populations of damaging flies, allowing beneficial insects within the pasture to assist with pollination, seed formation and soil pH balance.

From an economic standpoint, industry research shows additional benefits to insect control through minerals. When divided into a daily per-head basis, insect growth regulators can cost approximately four to six cents per head per day for all-season control.

Industry research shows returns on investment between 6:1 and 10:1 for a cow-calf pair investment of $4.50 to $5.50 for the summer feeding season.

Organophosphate insecticides provided through a spray will cost approximately three to four cents per head to purchase and apply the spray; however, the protection of the spray will only last a few weeks before it needs to be reapplied to a facility.

Ear tags formulated to keep flies at a distance are similar in pricing at about three to four cents per head per day. If ear tags are to be used, producers are encouraged to alternate the type of organophosphate to reduce the risk for insect resistance.

Many producers have seen benefits in combining insect growth regulators into their fly control strategies. Once the correct program is selected, the long-term impact potential on cow health, calf growth rates and yearling productivity are evident.

Ultimately, minimizing fly populations can enhance the productivity of the overall herd, creating less stress for your cattle and less stress to your operation’s bottom-line potential.


Studies show that cows with proper fly control can wean calves 10 to 15 pounds heavier than cows with heavy fly populations. Photo courtesy of Purina

drew shaine

Drew Shain

Technical Sales Specialist
Purina Animal Nutrition