Flies are more than just an annoyance to grazing cattle. Flies also can transmit diseases and stunt growth, says Ron Lemenager, Purdue University Extension beef specialist. Producers can protect their herds through proper sanitation and insecticides, he says.
"For grazing cattle we're really concerned about two different types of flies: face flies and horn flies," Lemenager says. "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.
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.
"The horn fly is a little different. 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. The horn fly can cause reduced weight gains."
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 non-lactating cow's mammary glands.
"These flies start becoming a problem about late May," Lemenager says. "By the middle of June producers should be thinking about fly control."
Control methods for face and horn flies on grazing cattle include insecticide treatments. Insecticides usually are applied directly to the animals, by various methods:
Insecticide-impregnated ear tags - Insecticide is gradually released from the tag through the animal's body oils. Cows spread the chemical when they groom themselves or their calves.
Dust bags - Insecticide powders are sprinkled over cattle as they walk under the bags hanging above gateways. Bags that contain oil-based insecticides are known as oilers.
Pour-ons - Concentrated insecticide is poured along the animal's top line.
Sprays - Insecticides are sprayed onto cattle. Some sprays come in ready-to-use forms, while others require dilution with water.
Feed-throughs - Cattle consume supplements or feed mixes containing a larvacide.
Horn flies are vulnerable to most control methods, Lemenager says. "The horn fly is very easy to control because it stays with the animal," he says. "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, because these flies will migrate from animal to animal. So you're probably best using insecticide sprays, impregnated ear tags, dust bags, oilers or some combination of them.
Producers should be careful which insecticides they use and how they use them, Lemenager says."There are some resistance issues with some of these insecticides," he says.
"Producers should visit with their local herd health provider or Extension educator about what's working in their area. 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."
Additional information about flies is available in Purdue Extension publications E-12-W, "Control of Cattle Pests" and E-206-W, "The Face Fly," both written by Ralph Williams, Extension entomologist. The publications are available online at Purdue's Beef Extension Publications Web page, at www.ansc.purdue.edu/beef/beefpub.htm .