Environmental Issues
Most geographic regions of the country experience economically damaging numbers of external parasites. These pests reproduce very quickly when temperature and humidity are ideal for their growth and an organic growth medium (such as manure) is present. The density of the pest population depends on other factors, such as the usage of biological control agents and density of cows in the housing areas. With the increased emphasis on the environmental responsibility of dairy producers and as residential housing developments and dairies become physically closer, fly control on dairy farms has become increasingly important.

The Department of Agriculture’s Grade A Pasteurized Milk Ordinance specifies the responsibility of dairy producers to conscientiously reduce fly populations on their farm. Dairy and health inspectors are becoming more conscientious of fly infestation on farms. Many local governments have implemented laws to regulate fly control and manure management. In addition, the number of law suits relating to fly infestation from farms and the impact of flies on residential areas, is growing. Dairy producers and their residential neighbors are becoming more aware of the nuisance and potential for flies to transmit dangerous diseases.

Profitability
The actual monetary loss from fly infestation is difficult to measure, but estimates range from 10% to 20% decline in milk production when dairy cows are heavily infested with biting flies. How do flies cause reductions in milk production and performance? First, attempts by the cow to alleviate irritation from biting and sucking flies increases maintenance requirements which impacts feed efficiency for milk production. Attempts to relieve irritation include shaking off motions, biting, rubbing, and tail switching which all increase heart and respiratory rates. An increase in body temperature is especially detrimental when the cow is also stressed by environmental heat. Because fly populations naturally increase during warm temperatures, differentiating between heat stress or parasite infestation or both may be difficult when a drop in milk production occurs.

A second reason that flies can cause a substantial loss in milk production is the increased nutrient demand which occurs in response to blood loss. When the blood-feeding fly population is significant enough to cause the cow’s body to divert nutrients into replacing lost blood, milk production may suffer.

The transmission of disease among cows by external parasites is yet another potential cause for reduced milk production. Flies transmit diseases including anthrax, brucellosis, tuberculosis, as well as Staphylococcus and Streptococcus mastitis infections. Mastitis bacteria can live up to 16 hours in a fly, which is more than enough time to transmit the bacteria from cow to cow.

Flies
On most dairy farms, five species of flies are predominant:

House Flies—These flies do not bite; however, they can be very irritating.
House flies prefer organic material containing 40% to 70% moisture (such as manure) to breed. These flies carry many different pathogens, and easily transmit disease.

Stables Flies—Unlike similar looking house flies, stable flies bite. Females require blood to reproduce. Males also draw blood from animals.

Horn Flies—These biting, blood sucking flies lay their eggs in fresh cow manure. Horn flies look like miniature house flies and are extremely irritating, causing cattle production losses due to energy and time spent fighting (stamping, tail switching, etc.).

Face Flies—These flies also resemble house flies, but are usually found on pastured cows. Face flies lay their eggs in very fresh manure. Face flies are not capable of biting; however, they feed on secretions commonly found on the faces of cattle, such as around the eyes. The face fly is most noted for transmitting pink eye.

Horse Flies—In comparison to other flies, horse flies are very large. Although horse fly numbers are generally low, it only takes a few to cause extreme agitation among animals due to their painful bites.

Fly Control on Dairy Operations

Sanitation
Because of the intensive management involved on dairy operations, the most effective fly control method is frequent removal of manure from barns, along with an integrated fly control program. Sanitation should be the first and is the most effective part of the fly control program. Sanitation involves:

• Removing manure frequently during the day.

• Hauling manure to fields or frequently pumping from lagoons.

• Cleaning up spilled feed immediately.

• Keeping bedding clean and dry.

• Filling mud holes or any low spots in lots where water can accumulate.

Insecticides
Use insecticides according to label directions, taking care not to contaminate feed, water, and milking equipment. Contamination of milk with insecticides is a concern. Permectrins are effective ingredients used in insecticide sprays for animals. Animal sprays can be applied in different forms.

Sprays—Insecticide animal sprays can be either oil- or water-based. Water dilutable sprays are more effective for high volume application, especially when power equipment is used.

Dust Bags—Dust bags use powdered insecticides and should be placed at the exit lane of parlors. To be effective, bags should hang four to six inches below the top line of the cattle.

Back and Face Rubbers—Oil-based insecticides are used in back or face rubbers. Cows should get an application of the insecticide at least twice daily. Placing oilers in the exit lane of parlors is most effective.

Foggers—Space sprays or foggers kill flies on contact.

Premise Sprays—Residual properties of these sprays enable them to be used effectively as premise sprays. Sprays should be applied to areas where flies hide, such as calf hutches, feed spill areas, stalls, pens, feed bunks, and hospital or maternity pens.

Other methods of fly control include the following:

Ear Tags—Ear tags can be an effective method of fly control when chemical insecticide resistance is not a problem.

Baits—Baits contain an ingredient to attract flies and an active ingredient which kills flies once the bait is consumed. Fly bait can be an effective method to kill house flies.

Biological Control
Some beneficial insects can provide control of harmful insects. Some beetles, wasps, or other parasitic insects consume fly larvae and pupae of harmful flies, thus reducing their numbers. Effectiveness of this type of program depends on intensive implementation and continuous monitoring. Insecticide use must be limited because it can kill beneficial as well as harmful insects. Specific numbers of beneficial insects needed as well as release procedures can be obtained from vendors that sell these products.

Feeding to Improve Fly Control
Methoprene, an insect growth regulator, is a proven effective means to prevent the breeding of horn flies in the manure of treated cattle. Horn flies are especially detrimental to cattle on pasture or anywhere manure is not disturbed for several days. It is not uncommon to observe horn fly counts of 200 to 1,000 flies per animal. A horn fly can bite and draw blood four to eight times daily. For a lactating dairy cow with 1,000 flies, the resulting 4,000 to 8,000 bites daily can cause an estimated 20% drop in milk production. Adult female horn flies leave their host for a few seconds and lay eggs in fresh manure. When eggs hatch and develop into adults, they find a host very quickly to begin feeding. In a couple days, new adult females will begin laying eggs and the reproductive cycle continues.

The best method to reduce horn fly numbers is to break their life cycle. When methoprene is fed to cows, it passes into the manure, preventing development of horn flies to the adult fly stage.

Horn flies are typically not found on dairy cattle held in confinement or dry lots. House fly and stable fly control products (such as fly baits, residual sprays, or low volume direct sprays) should be used to control flies in or near cattle buildings. However, when dry or lactating cows or growing heifers are on pasture during fly season, methoprene feed-through has been shown to be an extremely effective method to prevent the breeding of horn flies; thus, halting their development into biting, annoying adult flies. The result is a drop in horn fly numbers or containment of the horn fly population that could otherwise cause production losses.

Conclusion
Environmental issues and laws should be a major concern for all dairy producers. In addition, because of the fly’s ability to negatively impact feed efficiency, decrease milk production, and transmit diseases, fly control is important to profitability of every dairy operation. Sanitation is the most important part of the fly control program in and around buildings and dry lots and should be an integral part of the management program. In addition to sanitation, insecticides and feed-through agents are also effective and profitable methods if used as directed and on a regular basis for their intended purposes.