Insect considerations for livestock, equines help with disease control

Dr. AJ Tarpoff, Kansas State University Extension beef veterinarian, said diseases like vesicular stomatitis and external parasites tend to go hand in hand.

“We have to admit when we don’t know something,” Tarpoff said. “And what we don’t understand sometimes is exactly how some of these external parasites can play a role in transmission of diseases.”

Tarpoff spoke June 25 during a webinar hosted by Butler County, Kansas State University Research and Extension and the Kansas Department of Agriculture, Division of Animal Health. He took “kind of a big, wide swath” covering a number of different external parasites, explaining their behaviors so livestock producers have a better idea how to control them.

During the grazing season in Kansas, livestock owners must think about horn flies, stable flies and ticks—among others.

Horn flies

Cattle in pastures most commonly have horn flies on their backs and these flies are very specific as to where they spend their time. Most often they stay on the same animal and spend all their time there.

“They only leave that one animal to lay eggs in fresh manure and then they come back,” Tarpoff said.

Even though they’re blood meal feeders and can be a big hindrance to some production parameters, they do not necessarily cause any type of disease transfer because of feeding on a single animal.

“It can be pretty devastating,” he said. “Those are flies we really want to treat.”

Stable flies

Stable flies are not only found on cattle, but almost all livestock species, according to Tarpoff.

“If any of you have been around livestock, whether you’re in a stable with horses, whether you’ve been out working your cattle, and you see your horses or your cattle swishing their tails and stomping their feet and, as you get closer, you feel a super painful bite from a little black fly,” he said. “That’s a stable fly.”

Stable flies are found on the animal’s leg, where they tend to feed. This species likes to bite and it’s extremely painful.

“It does not take very many flies per animal to really cause an issue,” Tarpoff said. “We can see bunching behavior. We can see different types of avoidance behaviors, especially in our horses and our cattle.”

What’s interesting about stable flies is they tend to not spend very much time on cattle or other livestock. They come up, take a quick bite and leave.

“They only feed during the day, which is really unique about this fly,” Tarpoff said.

Stable flies also “love decaying organic matter,” and thrive in a moist environment. Here they lay their eggs and larva will develop. Feeding sites for round bales, alleyways, and other feeding areas will attract them as well.

“What’s unique about stable flies is during the heat of the day, after they take their bite, they will rest in shaded areas,” Tarpoff said.

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Historically, stable flies have been present in confinement situations, but they are also found “quite a bit” in pasture settings.

“You know why are we seeing it in pasture settings?” Tarpoff said. “A lot of that has to do with how we feed during winter months, or the confines that we have these animals in.”

Keep in mind, one round bale feeding site where animals were fed during the winter, will result in 1 million more stable flies in that given environment the subsequent year.

“Stable flies love that excess residue,” Tarpoff said.

Face flies

There are a couple of different species that are affected by face flies. These flies really like to feed on the secretions around the eyes and nose.

“Yes, they’re a vector for spreading pinkeye,” he said.

Face flies tend to lay eggs in fresh manure, similar to horn flies, but they also travel long distances between feedings. They’re not blood feeders, but their spongy mouth parts are like sandpaper and are abrasive.

“It can mechanically transmit a little bit of bacteria in some of these tissues, but they’re not a blood feeder,” Tarpoff said. “They’re difficult to control because they don’t spend much time on our animals.”

House flies

House flies are one of the biggest nuisance pests people routinely see on livestock and in the premises.

“But really, they’re more of a nuisance for us,” Tarpoff said. “We’ve documented that they can transmit different bacteria from one animal to another, but really this is a nuisance pest.”

House flies swarm in large numbers during different periods of the day. They can transmit a couple of things, in horses particularly, but spreading viruses and blood borne pathogens is not really how they feed.

“They will lay their eggs and open kind of perineal wounds,” Tarpoff said. “So even if we do have an infected, particularly vesicular stomatitis premise, some of those lesions may secondarily get a little bit of fly strike because these house flies will congregate to some of those lesions on the outside.”

House flies tend to rest in sunny areas, as opposed to stable flies who prefer shade.

“So if you look on the side of your barn or the side of your house during the heat of the day and you see massive numbers of flies on the side of your horse shed, believe it or not, those are house flies,” he said.

Vesicular stomatitis vectors

Vesicular stomatitis, a viral disease primarily affecting horses and beef cattle, occasionally strikes swine, sheep, goats, llamas and alpacas, and leaves lesions on the animals mouth, coronary band on hooves, legs, ears and underlines. Some of the known vectors are biting midges and black flies, also called buffalo gnats. These small, blood feeders have a pretty painful bite. These types of vectors lay eggs in organic matter, in and near streams.

“We’ve seen the trend of following different tributaries and waterways and much of that has to do with where they lay their eggs and where they thrive,” Tarpoff said.

Minimizing access to some of these pests’ environments during critical times can be part of the management strategy. Black flies are daytime feeders, and tend to feed on the head and neck. Tarpoff suggested the lesions on ears pictured during the webinar could be attributed to the black fly.

Biting midges feed around dusk and during the late evening.

“That’s when they come out and that’s where they really thrive,” he said. “They feed on the dorsal and the ventral, so the top of the back and underneath the belly—that’s where they feed most of the time.”

Control and treatment of external parasites

Tarpoff said there’s a lot of product usage and treatment options available to livestock producers when it comes to external parasites.

“If I had a list it would be about a mile long and wide about how much we actually have,” he said.

Feed-through products can be very specific to a certain parasite—ear tags, pour-ons, sprays, dusters or oilers, even a gun applicator.

“Within the parasiticides, we have a couple of different classes that we generally utilize in our livestock,” Tarpoff said. “We have some feed-through products that we generally refer to as insect growth regulators that can affect some of these fly species and then we have the true insecticide.”

Tarpoff warned though, resistance to these types of products is very real.

Resistance means the intended target no longer responds to the product like it used to. That generally occurs because there’s either too low of a dose for a long period of time or the insect is exposed to the same insecticide classes for multiple years in a row for long durations of time.

Feed-through products are generally available for cattle, horses, swine and poultry.

“These are products that are fed to the animal,” he said. “They do not affect the animal. It gets passed into the manure, into the environment where some external parasites will actually lay their eggs, and that’s how they actually interfere with the general population in an area.”

The most effect from some of the feed-throughs can be seen if they’re fed before the vector season begins. But producers really can’t rely only on the feed-throughs, since the insects can still fly quite a long way.

Ear tags can help

Ear tags for cattle with insecticide impregnated in the material can be effective. But producers must remove them at the end of the season to help with resistance.

“If we don’t remove them at the end of the season, we can actually incur more resistance issues in the next few years,” Tarpoff said. “We can have season-long duration with these as we have constant exposure since they’re constantly on the animals.”

Tarpoff reminds producers to rotate these appropriately as most flies create resistance to pyrethrins quicker than some other chemicals.

“We can do a pyrethrin no more than one set of every three years followed with an organophosphate for two years,” he said. “If you have questions about this, please visit with your local veterinarian.”

Pour-ons and sprays don’t generally carry quite as much resistance or risk to develop resistance, and that’s because they don’t have much residual activity.

“The residual activity with ear tags is because we have constant exposure for up to five months,” Tarpoff said. “With pour-ons and sprays, they get into the environment, they work, and they go away.”

For most of the pour-ons and sprays efficacy is usually around two to four weeks, and they don’t prevent the pests from coming and taking a bite. It actually works by contact.

“They actually have to come and bite the animal for them to be effective,” Tarpoff said. “It’s not like spraying OFF or anything on ourselves, we don’t have the repellent activity from a lot of these products.”

Additional sprays

Premise sprays can also be used to help alleviate the fly pressure in an area. There are a couple different types and short-term sprays work by killing adults. These have no residual activity, and can immediately knock back the adults.

Residuals, or regular premise sprays, are what is most commonly mixed into pump sprayers and cover the areas where these parasites may live. They are very effective in a lot of different situations.

“We will actually get coverage for up to four weeks or so, which is great,” Tarpoff said. “But please keep in mind, especially when we’re using these products in the environment, please follow label mixing and application directions.”

There are a variety of self-treatment applicators out there where the animals can rub on or walk under, but Tarpoff said to remember, not all animals will utilize these when in a group.

“If you do have a group of animals—say there’s a group of cattle—and you’re using some of the self treatment dusters, oilers or rubs, make sure that there is a little bit of unique fencing around strategic areas and force them to use them on a daily basis,” he said. “We’ll get maximum effectiveness.”

There’s also a variety of other products on the market—paintball insecticides, parasitic wasps, and other items. Consult your local veterinarian for the most effective products on your location.

For horses, many of the same cattle-approved products are also approved for equines.

“What’s unique with equine is there’s also many repellent products that are available,” Tarpoff said. “Both shampoos or ointments that can be rubbed on the ears, sprays, but these repellent products, they are not long lived. They’re very short acting, and generally we have to apply these products almost daily. So it’s pretty labor intensive.”

One final thought, environmental management.

“Cleanliness is the key to external parasites,” he said. “Managing manure, making sure we’re disrupting and we’re not leaving piles of older manure areas that are heavy traveled.”

Flies can’t thrive in areas that are heavily traveled; instead it’s the undisturbed manure piles or pen floors that have manure on them. So cleaning and scraping becomes important. Disturbing the manure filled areas to get them as clean as possible is important. Don’t forget about heavy vegetation, either on fence lines or drainage ditches.

“Making sure that if we can knock down vegetation on our fence lines and around our perimeter, that’s a pretty good step to take and controlling external parasites,” Tarpoff said. “Any area that we have water holes and things like that. If it looks like it’s going to harbor mosquitoes it can probably harbor some of these other parasites as well.”

Kylene Scott can be reached at 620-227-1804 or [email protected].