Stocker fly strategies to minimize the damage flies cause cattle.

When margins grow finer than a flea's whisker, some performance management tools can look more luxurious than necessary, especially if results are hard to see with the naked eye.

For instance, Alberto Broce, Kansas State University (KSU) professor of entomology, says stocker operators never realize the damage that flies can cause until cattle hit the scales at the end of the summer grazing season. “Often, producers don't have any idea what it costs them,” he says.

Unchecked, the most common stocker fly pests — face flies, horn flies and stable flies, each can take sizable bites out of performance. For instance, horn flies and stable flies are both bloodsuckers whose painful bites can take a toll of more than 0.5 lb./day in gain.

Face flies, on the other hand, irritate eyes already made fragile by the ultraviolet rays and dust of summer, helping create a productive environment for the Moraxella bovis organism. It's the common culprit behind pinkeye, which the flies also spread from one animal to another.

According to the 1997 National Health Monitoring Service Cow/calf Health and Health Management Practices Report, pinkeye costs the industry about $150 million annually. That's in treatment costs, as well as lost weight gains and milk production.

No surprise then that producers responding to KSU's landmark Beef Stocker 2000 Survey cite pinkeye as one of the most prevalent health challenges they face in cattle 30 days and more after receiving.

Even producers who understand the potential cost of flies and who struggle to control them can find the exercise akin to branding the moon. Flies that are a problem one year may not be the next; products that seemed lethal one year apparently lose their steam the next, and on and on.

Horn flies — the primary pest of pastured cattle — swishing tails are the barometer.

“Since the development of the insecticide resistance problem in horn flies, we've learned important facts about the biology of these flies that producers can use in controlling them,” says Broce.

For one, horn flies are transient pests, moving helter-skelter among a group of cattle. That means not every animal in a group needs to be treated in order for every animal to receive protection. In fact, Broce says the closer to 100% horn fly control within a group of cattle, the faster the flies become resistant to the particular control being used.

“We've also learned we don't need to achieve 100% control of horn flies to prevent the losses they can cause,” says Broce. “Cattle can withstand the attacks of a low number of horn flies without showing any effect on weight gain or performance.”

To control horn flies while battling a build-up in resistance, Broce recommends alternating season to season between organophosphate and pyrethroid products. That's whether the application is eartags, sprays, pour-ons, back-rubbers, dust bags or feed additives.

As for endectocides that control both internal and external parasites, given the mobility of flies, Broce recommends using them to control internal parasites and viewing any control of external parasites as gravy. In other words, these products certainly may reduce the horn fly population a pasture is producing, but they can do nothing to prevent flies from moving in from other pastures.

“In addition, some of these chemicals can be detrimental to dung beetles developing in cow pats,” says Broce.

Face flies — indicated by ear twitching and head tossing.

“Pyrethroid tags remain effective against face flies. Insecticide tags still offer the highest level of face fly control (about 70%),” says Broce. In areas where reduction and prevention of pinkeye transmission is key, he recommends supplementing with an additional and different method of control, primarily to prevent build-up of resistant horn fly populations.

To prevent pinkeye, Harold Garner, Otter Creek Ranch, Eureka, KS, takes the nutritional and stress reduction approach in his stocker pastures. He also feeds chlortetracycline in his mineral, he says, because he says research indicates that feeding chlortetracycline — FDA-approved for low-level feeding to prevent liver abscesses — also reduces incidence and severity of pinkeye, as well as footrot, another common and vexing stocker health challenge.

With mineral in mind, Roger Bechtal of the Bechtal Ranch, Eureka, KS, also emphasizes nutrition as the foundation of a health program. He makes sure he keeps a balanced mineral and trace mineral program in front of his stocker cattle. He also feeds chlortetracycline, along with iodine, in the mineral for prevention.

“I wouldn't just take things for granted, either. Things are always changing, and with new technology, you can come up with better evaluations of what you have,” says Bechtal.

Finally, given the research and practical experience underscoring the value low stress plays in cattle health, Garner says, “Something that has helped us as much as anything is using a dart gun to administer treatment and not having to hassle the cattle as much.”

Stable flies — look for tail switching, feet stomping and bunching.

It used to be that stable flies were viewed as a challenge only in confinement situations such as feedlots and dairies. Turns out, these are the Charlie Lindberghs of the fly world, able to move with the wind as far as 155 miles.

“Ask anyone who had cattle in pasture around here last summer if they saw cattle bunching up,” says Broce. It's a sign of cattle seeking protection from stable flies. “We saw a lot of cattle standing in ponds or lying down to protect their legs.”

In fact, Broce says that in north central Kansas last summer, researchers trapped as many as 820 stables flies/trap/day in pastures. In the feedlot, he explains 150 flies/trap/day is the flashpoint for taking action against them.

Unfortunately, Broce says no efficient chemical control is available for stable flies in the pasture. Consequently, control is about preventing stable fly reproduction rather than picking them off with insecticides.

“Research we did last summer identified winter feeding grounds for round bales as a major source, perhaps the primary source, of these stable flies in pastures,” he says.

Depending on the feeding method, Broce says cattle waste as much as half of a round bale. This hay waste mixed with urine and manure makes an ideal breeding habitat for the flies. Adding insult to injury, Broce emphasizes no chemical application can be applied to the hay ground to control developing stable fly maggots.

With that in mind, Broce suggests reducing the amount of hay waste, reducing overuse of the same ground for feeding, making sure cattle aren't supplied with more feed than they need, and plowing the feeding grounds after winter feeding.

Incidentally, Broce also mentions, “In the past 10 years we've observed what appeared to be failures of insecticide treatments against horn flies in the pasture. Upon investigation, many of these situations turned out to be high populations of stable flies.”

Product And Timing

More than anything, Broce and other veterinarians say zapping flies and the profits they steal requires identifying the fly and then using the right chemical in the right application at the right time. For instance, a particular eartag may be exactly what is needed in a given situation, but if it's applied too early, the active agent may be the weakest when the flies are the heaviest, Bechtal says.

“It's not because there's anything wrong with the tag,” says Bechtal. “It's just the time factor.”

Of course, avoiding flies is an effective strategy, too. In this case, fly control is another benefit some stocker operators attribute to intensive early-season grazing — doubling the stocking rate and halving the pasture time to roughly two and a half months.

“I'm an enthusiast of intensive early stocking because of its benefits in reducing the damaging effects of horn flies and face flies,” says Broce. “An additional benefit is that by taking the cattle out of the pastures in mid-summer (July), there will not be any face flies and horn flies to start new populations next spring.”

In the Flint Hills where Bechtal runs his cattle, flies start cropping up toward the end of the summer season in August and September, depending on the pasture and the location, Bechtal says. So, intensive early season grazing allows some folks to miss the glut of flies.

Bechtal's bottom-line strategy is simple: “Don't be lulled into complacency; always be asking questions.”

For more detailed information on fly control and other stocker management issues, visit