Insects can pose a challenge to livestock and impact performance, but there are steps producers can take to reduce their numbers.
Iowa State University Extension veterinarian Grant Dewell says there are many tools breeders have to combat fly problems, but a good first step is to limit their ability to breed by identifying the type of flies.
“Different flies have different breeding grounds,” he says.
Dewell says horn flies and face flies are major pests of grazing livestock. He says horn flies are the most economically harmful external parasites of grazing animals, and can reduce weights and growth rates. They spend most of their time on the backs and shoulders of grazing animals and lay their eggs in fresh manure.
Face flies also lay eggs in manure and congregate around animal faces. They are similar in size to house flies and are twice as large as horn flies. They don’t feed on blood, so they don’t have a direct impact on cattle growth, but they can cause lower weaning weights by decreasing milk intake.
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Dewell says disturbing fresh manure, such as using a harrow in pastures, can reduce fly populations in pastures.
“One thing is just good pasture management,” he says, “so they break up those faecal flushes.”
Ric Bessin, professor of entomology at the University of Kentucky, says insect management works with chemical control options.
“There are other methods to complement chemical control,” he says. “Maybe not as a replacement for chemicals, but so we’re not relying on chemicals alone.”
In feedlots, manure dung is frequently disturbed, naturally destroying the insects’ potential breeding ground. In extensive grazing situations, cattle are less likely to disturb manure.
“Use some sort of trail to disturb them and spread them out,” Dewell explains.
Bessin says the disturbing manure pats can help dry them out and eliminate them as a spawning ground.
“It’s very beneficial,” he says. “The longer this patty stays wet, the more breeding ground it is for several species of flies that harm livestock.”
Bessin says working in pastures to limit wetlands can also reduce insect populations.
“The more we can manipulate the pastures and not have these wet areas on the farm, improve the drainage, that can improve the pest issues on the farm,” he says.
These efforts are aimed at reducing the number of harmful insects and making them easier to deal with, Bessin explains.
“It’s not going to totally eliminate the pest population, but what we’re trying to do is reduce those populations to a manageable level,” he says.
Producers may also consider using insect growth regulators in manure pats.
“It does a really good job,” Dewell says.
In feedlots, stable flies are more of a concern than horn and face flies. They lay eggs in decaying organic matter such as old leaf litter or muddy grass.
“We have to be pretty aggressive in cleaning up this organic material,” Dewell says.
He says growers can also introduce parasitic wasps, which naturally reduce adult fly populations by inserting eggs into fly pupae and disrupting fly development.
“Finding a reputable supplier and releasing wasps periodically throughout fly season can yield the best results,” he says.
Beyond reducing breeding populations, farmers have some chemical fly control options, including sprays and spills, feed additives, back rubbers, dust bags, and ear tags.
“We have a lot of tools available,” Bessin says.
Ear tags can be helpful in controlling horn flies.
“Insecticidal ear tags are primarily designed for horn flies, and they’re good for that,” Dewell says.
For face fly problems, he says treated face wipes can help keep flies away from pets. Putting these insecticide-impregnated wipes in front of mineral feeders can apply some protection to faces when animals come in to eat.
Bessin says growers should always work to combat resistance, so they shouldn’t just use the cheapest fly control option year after year. He says constantly reusing a mode of action can make pests more tolerant, and instead they might try using three different tactics in rotation.
Fly control remains a critical issue, as Dewell says their impact on weight loss and performance is “well documented”.
“Stable flies have a very painful bite,” he says. “It doesn’t take much to antagonize cattle, dab their food and stay away from feeders.”
Bessin says to monitor flocks, and if horn fly populations reach more than 100 flies on an animal’s side, or more than 200 per animal in total, it can start to have bigger impacts on the performance of the livestock.
“If you exceed that, it will really lead to a reduction in gain,” he says.