"We tend to think about them as they are bothering us and bothering the animals, but they are actually costing the producer money," Wolfgang says. Cows that are stressed from constantly swatting flies spend less time resting and eating, therefore dry matter intake decreases.
Milk yield can be impacted by as much as 25 percent, he adds. The effects on heifers and beef cattle manifest as a reduction in daily gain that could range from 0.5 to 1 pound per day. Animals that have docked tails may experience even more negative effects of flies if a proper control plan is not in place.
"It can be expensive to not have a good fly control program," Wolfgang notes. In general, all species of flies lay oval-shaped eggs. Before females can lay their eggs, most need a protein meal. For some, this may be found in the sweat, tears, saliva and manure of cattle. Others are seeking blood.
Females then look for moist areas to provide the ideal environment for laying their eggs. On the farm, piles of manure, rotting vegetation and mud are often the chosen location. Some may even seek to lay their eggs in areas of open flesh on a cow's body.
Upon hatching, the life cycle of the fly begins as a larvae (maggot) which develops into a pupa before emerging as an adult. A basic understanding of this cycle is necessary for proper pest management because not every product attacks every stage, Wolfgang points out.
While sprays may take care of the immediate adult population, the next generation is likely only a few weeks or even days away from taking its place. House flies, for example, may produce up to 12 generations in the course of a summer because of their short life cycle.
This common species lays its eggs in manure piles or decomposing piles of garbage or feed, with adult flies emerging in as little as a week. Face flies are another common pest. Their life cycle completes in around two weeks. They are often found around the fresh manure piles where females lay their eggs or congregating around the eyes and muzzle.
Because face flies travel in a large radius, they may carry bacteria from one farm to another, spreading diseases like pink eye. Wolfgang says that there are several vaccines available to prevent pink eye, and mid to late spring is the ideal time to administer them for protection early in the fly season.
Ear tags may also help reduce the incidence of pink eye. Stable flies may look similar to house flies but tend to be more gray in color with four dark stripes. While face flies tend to stay out on pasture, stable flies follow animals into the barn, seeking a meal of blood along a cow's lower body. They lay their eggs in wet straw, old bedding or manure, and the new adults hatch out within four weeks.
Possibly the most damaging among the common fly species is the horn fly, according to Wolfgang. Swarms congregate around animals all day, particularly on the back, poll and withers. They may be either resting on the animal or feeding on blood, taking up to 40 meals each day.
The horn fly life cycle completes in 10 to 14 days. Cows and heifers on pasture, especially near wooded areas, may also be bothered by deer flies and horse flies that feed on large mammals. The painful bites can cause blood loss at as much as 100 milliliters per animal per day.
Heel flies and cattle grubs, which were once also devastating pests, are not near the problem today that they once were. Thanks to pour-on insecticides, fewer animals suffer from grubs that burrowed under their skin throughout the winter and hatched in early spring.
Wolfgang recommends applying treatments in late summer or early fall to keep this problem controlled. Flies can also lead to health concerns like mastitis. As house and stable flies land on the skin around the teat end, they can transfer bacteria from one animal to another.
Coliform mastitis can be spread when pastured cows group together for shade, providing a small area for flies to transfer from cow to cow and udder to udder. To prevent this, Wolfgang encourages excellent milking protocols including using a barrier teat dip.
Fly control on the pastures and fans in barns may also aid in preventing flies from spreading coliform. Biting flies can also carry bacteria onto and into udders and teats, he adds, leading to staph aureus infections that thrive in damaged tissue.
This is particularly a concern in heifers that may come in fresh with the infection. That is why dry cow or lactating cow tubes are sometimes used as part of the pre-calving therapy; however, Wolfgang reminds us that would be considered extra-label drug use (ELDU) and if therefore subject to further oversight and possibly longer milk withholding.
FLY CONTROL STRATEGIES
Controlling the physical environment is the first step in the three-pronged approach to fly control, which also included biological and chemical control. "Calf hutches can be a fly factory in the summer," Wolfgang says.
Remove manure or stir bedding every 10 days or less to interrupt the life cycle of the flies. Also, keep weeds, brush, feed piles and garbage to a minimum to eliminate places for females to lay eggs. He recommends composting, stacking or agitating manure.
Nature provides effective means of controlling flies. Biological controls like parasitic wasps can be purchased and introduced to keep the population in check by attacking fly pupae. Certain beetles and mites also feed on fly eggs and larvae.
Wolfgang warns producers to be cautious with pour-on insecticides because some will kill not only harmful parasites, but also helpful beetles and mites. Chemicals may be used to reduce flies in the environment and on the animal itself. Space sprays provide short-term relief by knocking out adult flies, while residual sprays provide longer relief.
He cautions to heed the label directions on these products, as some may affect the milk supply. When treating the animal, read the label to see which parasites sprays and pour-ons control. The avermectins generally do not kill flies, but they are effective on grubs, ticks, mites and lice.
Larvicides may be given to the animal with the feed or as a bolus to kill larvae that may grow in manure. By incorporating these three control methods, Wolfgang says we can develop an effective integrated pest management program to improve animal well-being and reduce the need for chemicals. "If we use these together in concert, we can often use those chemicals smarter and in less concentration," he adds.
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