Use insecticides correctly — year to year — to keep your calves gaining and your herd healthier.
By Michael Barnett
Ranchers might be their own worst enemy when it comes to addressing insecticide resistance in horn flies and other cattle pests.
The economic penalty is severe for not controlling horn flies, the No. 1 cattle pest in Texas. But using insecticides incorrectly can lead to far bigger problems, says Dr. Larry Hawkins, a technical services veterinarian with Bayer Animal Health.
Pesticide resistance should be top of mind for every rancher, he suggests.
“Ultimately, if we do not have a good product to use because there is resistance to it, then everybody loses.”
The economics of control
A key question facing ranchers is not how much insect control costs. Rather, it is how much more can I make with proper control?
Pests affect production and, therefore, our net income.
“Livestock spend time fighting flies and they expend energy doing it, so they do not graze,” Hawkins says. “There is a real cost that comes with flies.”
Research in Nebraska shows that cows without horn fly control weaned calves that were 11.8 pounds lighter, and Hawkins says that other data suggests losses of 12 to 15 pounds in weaned calves when flies were not controlled on their mothers.
“You know, 12 pounds at a buck fifty is $18 per head,” he says.
“The cost of control is a bargain in terms of benefit. For example, two ear tags per cow at roughly $2 each will cost $4. Adding a little product around the mineral feeders via dust bags or oilers during the fly season will cost another $1.50. Spending $5 to $6 to get $18 back ($1.50 per cwt) “is a no-brainer, so why not?” Hawkins asks.
Stable flies are another pest and like horn flies, take money out of the rancher’s pocket. Some research shows losses of up to a half pound per day on weaned calves when stable flies are not controlled. Fortunately, stable flies tend to be less of a problem when it gets hot.
Liver flukes are a problem on the Gulf Coast. They do cause production concerns, especially when they are found in high levels in a herd.
Ticks can cause anaplasmosis, which may cause infected cows to abort their calves. Even if infected cows do not abort calves, the offspring can become infected and will be carriers of the disease for life.
Fever ticks, found only in a quarantine zone along the Texas/Mexico border, could become a crisis not only for Texas but for the cattle industry in the U.S. Fever ticks are the vectors for microscopic protozoa responsible for cattle fever, which causes acute anemia, high fever, enlargement of the spleen and liver, and ultimately results in death for up to 90 percent of the cattle who have never been exposed.
“It is a concern for the entire cattle industry,” Hawkins says. “South Texas, fortunately for the rest of the nation, is the only place we see it.”
Resistance has been a problem with fever ticks for decades.
Managing against resistance
“It has always been an issue,” Hawkins says. “In the 1950s, there was beginning to be resistance in fever ticks. We are concerned about horn flies every year.”
That is because horn flies in the Southern states have 15 to 18 generations annually, giving flies a head start on resistance if a rancher is not using best practices for control.
To prevent a resistant insect, minimize exposure to low levels of pesticides, Hawkins says.
He explains it this way. If you have a gallon jug of pure pesticide and a bug crawls in it, the bug is going to die. When you mix that gallon with 50 gallons of water and spray it, almost all the insects die when it makes contact. Consider what happens when a bug lands on that animal and the pesticide in the spray or backrub has been diluted to 1 percent.
“Then that fly can live. Maybe it is sick, but we are selecting for a resistant bug. We kill all the ones that are susceptible and the only ones left are the ones that are resistant,” Hawkins says.
“It is important to follow the label instructions on insecticides. Animal health companies will determine the amount needed to kill a fly, for example, via a dose calculation. If you use a percentage of that dose to try to save money, you may kill most flies.
“If you kill 95 percent of the flies and have five flies left, you are eventually going to have a resistance issue,” Hawkins says.
Another problem is using the same insecticide year after year. Ranchers need to rotate exposure between different classes of insecticides.
If you use a pyrethroid class one year, you need to use an organophosphate the next. Those classes of insecticides have different chemical structures that affect insects in totally different ways.
Hawkins says that Bayer often recommends using a pyrethroid one year, then an organophosphate for probably two years, and then rotating back to a pyrethroid, so that the insects are not exposed to the same insecticide for an extended period.
Switching brands of insecticides is not enough, he stresses.
“Switching from pyrethroid 1 in one brand to pyrethroid 2 in another is not a rotation because they are going to work in the same location in the body”. “A real rotation is switching to organophosphate 1.”
He says that companies like Bayer are working hard to address resistance. They try to inform ranchers through meetings and develop and distribute information on what needs to be done.
Contrary to what many ranchers think, the recommendation of an animal health company representative is not meant to sell more product. It is an effort to extend the life of the product.
Bringing a new insecticide to market is a difficult task, especially if it is to be used on a food animal. It is expensive to conduct safety studies. And if the studies show that “one out of every 100,000 people is sensitive to that, then maybe we cannot use it as a food animal product,” Hawkins says. “It is important to develop new products, and screening of those products run all the time. But to complete the journey to a usable product is not all that common.”
Resistance control examples
What would a typical program for resistance control look like? Hawkins uses horn flies as an example.
A common recommendation is to wait until a few flies start bothering the cattle. He then suggests running them through the chute, attaching ear tags and using some type of pour-on to get a jump start on the population.
That should provide four months of protection. Most ear tags, no matter who makes them, say they release insecticide from the plastic for 150 days. Hawkins says they are most effective up to the 120-day mark.
Horn fly season is typically longer than 120 days in Texas, so decisions must be made again toward the end of the fly season to address both control and resistance.
One method is to put dust bags and oilers around the mineral feeders, keeping insecticides at recommended dosages. Some ranchers will replace old ear tags with new ones.
“Most of the time, producers have to think toward the end of the season. They need something a little extra to support their control efforts,” Hawkins says. “But if you control fly numbers early on, you will have fewer flies all season and pick up some of the benefits of not having horn flies for the entire season.”
Johnnie Segura, who works with the stocker operation at Schmidt Land and Cattle Company in Schulenburg, takes a different approach. He receives 250- to 300-pound sale barn calves, puts them out for 60 days, preconditions, then ships them to a feedyard.
Depending on the weather and the grass, he will often start a new batch of calves in late spring or early summer in Schulenburg, when horn fly action heats up.
Last year he used a Bayer pour-on, Permectrin CDS, when the calves came in, primarily because it is an affordable control measure that provides a quick kill. Three or four weeks later, he hit them again with the same insecticide. That provided the control he needed for 60 days.
He cannot tell you the real economic return, but he feels that the investment for control is a wise choice. He knows a heavy fly infestation will knock the calves off their feed.
“When flies get bad on the cattle, you can just see them constantly shaking their heads, twitching their tails, and stomping their feet,” Segura says. “It does add some stress to them; it goes down the line and affects their health and well-being.”
Segura is taking steps to prevent resistant flies. Instead of Permectrin CDS this year, he may use fly tags.
“It depends on what the active ingredient is, and we have to look at the cost,” he says.
Bottom line, be it a stocker or cow-calf operation, Hawkins suggests that ranchers consult a veterinarian, Extension personnel or an animal health technical service representative to develop an effective control plan that addresses resistance for every pest.
“Then stick to the plan and follow it to the letter.”
The location of the fly on the cattle can help you determine which pest you are working to control.
The house fly is a filth fly, feeding on manure, old feed, waste, sweat, and tears. These flies transmit disease just by landing on the cattle and have been known to carry up to 65 diseases.
Commonly found on the lower legs of the cattle, stable flies feed on blood. Their bite is painful, and they usually take two to three bites to get a satisfactory blood meal. Stable flies generally cause cattle to bunch up to avoid their bites.
The face fly feeds on nasal secretions and tears of cattle. They are known to transmit pinkeye in cattle and present the risk of transmitting bacteria and other viruses.
The horn fly bite is not as painful as that of a stable fly, but it does feed on the blood of cattle. Horn flies typically bite 30 times per day and are found on the back and sides of the animal. Cattle swish their tails to shoo the horn fly away.
One hand, 100 flies
To help producers calculate the number of flies, Bayer Animal Health estimates that 100 flies can fit in the area covered by an average-size hand — fingers, thumb, and palm included
Gain Pounds, Gain Dollars is excerpted from the April 2019 issue of The Cattleman magazine. Join today to start your subscription.
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