Flies are more than just annoying

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WEST LAFAYETTE, Ind. – There’s more than just lush grasses around cattle pastures these days: flies.
The winged intruders are more than just an annoyance to grazing cattle. Flies also can transmit diseases and stunt growth, said Ron Lemenager, Purdue University Extension beef specialist.
Producers can protect their herds through proper sanitation and insecticides, he said.
Two types. “For grazing cattle we’re really concerned about two different types of flies: face flies and horn flies,” Lemenager said.
Face flies tend to feed on secretions around the eyes and noses of cattle. They move from one animal to the next. The face fly is a major vector for M. bovis, which is a bacteria that can cause pinkeye.
The horn fly is a little different, Lemenager said. That particular fly is much smaller in size and tends to stay with the same animal, leaving that animal only to deposit eggs in fresh manure patties and then returning to that animal.
The horn fly is a bloodsucker and tends to feed on the back, withers, neck and sides of animals. It can cause reduced weight gains.
No fun. Face flies are similar in size to common houseflies. They feed without piercing the cow’s skin. In addition to carrying the bacteria that causes pinkeye, face flies also can transmit eyeworm and infectious abortion.
Horn flies are about half as big as face flies but no less troublesome. The flies inject their tube-like mouthparts into cattle and draw blood for food.
Horn flies can feed as often as 30 times per day. The feeding causes stress for animals, often leading to weight loss.
Horn flies also can spread summer mastitis, a disease affecting a nonlactating cow’s mammary glands.
Control. Horn flies are vulnerable to most control methods, Lemenager said.
“The horn fly is very easy to control because it stays with the animal,” he said.
Fly sprays, insecticide-impregnated ear tags, back rubs with insecticide and dust bags are pretty effective methods of control.
“We also can use feed-throughs, in which you’ve got insecticide that’s part of a mineral or supplements that you might purchase commercially.”
The feed-through insecticide passes through the animal into the manure, and then it breaks the life cycle of the fly before it can become an adult. It works primarily on the pupa stage of larval development.
Producers have fewer control options for face flies.
“The face fly is a different critter,” Lemenager said. “The feed-through insecticides don’t work quite as well if you have neighbors who are not controlling their flies, because these flies will migrate from animal to animal. So you’re probably stuck with using insecticide sprays, impregnated ear tags, dust bags, oilers or some combination of them.”
Read the label. Producers should be careful which insecticides they use and how they use them, Lemenager said, and there are some resistance issues with some of these insecticides.
Producers should visit with their local herd health provider or extension educator about what’s working in their area, Lemenager said.
“We’re probably going to have to switch the insecticides we use from one year to the next, so that we don’t develop a significant resistance problem.”

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