Page 29 - April 2022 Parker County 4-H Connection

Fly control important for livestock health
By Jennifer Dorsett
Field Editor

External parasites aren’t just an annoyance to livestock. The extra energy expended by constant head-tossing, stomping and overall restlessness of
animals affected by flies detracts from milk production, weight gain and other markers of livestock performance. But flies are also vectors for
livestock disease, according to A.J. Tarpoff, Kansas State University Extension beef veterinarian. In a recent webinar, Tarpoff discussed a variety of
external parasites and ways ranchers can control them.
“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.”
Stable flies

Stable flies are found on almost every livestock species. “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—that’s a stable fly,” Tarpoff said. Stable flies are found on the legs, sides, back and belly of large
animals or on the legs, head and ears of small animals, according to Texas A&M AgriLife Extension Service’s Livestock Veterinary Entomology
division. Tarpoff said unlike other fly species, the insects only come into contact with livestock when they feed. Stable flies rest elsewhere than on
the animals when not feeding. “They only feed during the day, which is really unique about this fly,” he said. “What’s unique about stable flies is
during the heat of the day, after they take their bite, they will rest in shaded areas.” Eggs and larvae are found in decaying organic matter such as
decomposing straw on the ground near round hay bales. Larvae are also commonly located in wet straw bedding, algal mats, wet grass clippings,
accumulations of manure and partially composted bedding and crop by-products. “It doesn’t take very many flies per animal to really cause an
issue,” Tarpoff said. “We can see different types of avoidance behaviors, like bunching, especially in horses and cattle.”
Horn flies are not an important vector of animal pathogens, according to AgriLife. But they can cause cattle to consume less feed, grow at a slower
rate and convert less feed into body mass. Bunching behavior will lead to increased body temperatures, which can lower milk production in dairy
cattle. Control of adult stable flies is difficult, so it’s best to prevent breeding where possible.

Horn flies
Horn flies are the most damaging insect pest of beef cattle in Texas, according to AgriLife. Research shows a calf infested with more than 200 horn
flies will weigh 15-20 pounds less at weaning, and horn fly infestation in dairy cattle can reduce milk production up to 20 percent. Horn flies look
like house flies and stable flies but rest on an animal between feedings. They feed on an animal’s back, shoulders and sides and often stay on the
same animal. “They only leave that one animal to lay eggs in fresh manure, and then they come back,” Tarpoff said.
He noted horn flies do not necessarily cause disease transfer, because they feed on a single animal. The economic and productivity losses, however,
are significant enough to warrant control. “It can be pretty devastating,” he said. “Those are flies we really want to treat.”
The best horn fly population control technique uses an integrated pest management approach in which cultural, biological and chemical methods
are employed.

28 PARKER COUNTY 4-H CONNECTION / APRIL