Horn flies and face flies can be two of the most economically damaging pests to your stocker operation. Maintaining appropriate control of these flies can help ensure that your stocker cattle achieve their gain potential and your profit expectations. Horn flies can reduce weight gains by 15 to 50 pounds during a grazing season, while the economic losses from face flies usually are associated with pinkeye, a contagious disease that affects the eyes of cattle.

Horn flies

Entomologists claim the horn fly is one of the most serious pests of cattle. Economic losses to horn flies amount to hundreds of million of dollars per year in the United States. Specifically, horn flies pierce the skin of cattle to suck blood, often taking up to 20 blood meals per day. The resulting pain and annoyance interferes with feeding, resting and the other normal activities of cattle.

Reduced weight gains of 15 to 50 pounds would equal economic losses of $15 to $60 per animal in today’s cattle market.Large populations of horn flies may cause open sores on the head and underline which can predispose their hosts to secondary infections of both disease and parasites. Because of their piercing-sucking mouthparts, horn flies are suspected of mechanically transmitting anthrax and other diseases within a herd.

Horn fly numbers of 50 or more per lactating dairy cow or 200 or more per beef cow are considered to be of economic importance. Extreme numbers of 10,000 to 20,000 flies per animal have been reported and could make blood loss alone (0.5 gal/month) an important factor in reduced production. Horn fly populations have been generally noted to be lower on dairy cattle than beef cattle. The feed ration fed to dairy animals greatly affects the fly's survival in the manure.

Horn flies remain on the host except when laying eggs or migrating to new hosts. Their close association with cattle makes them susceptible to chemical control measures.

Ear tags and forced-use dust bags give the best control, although sprays or dips may be used successfully. Dust bags may be hung in exit alleyways from barns or placed between pasture and water or feed. Dust bags will provide effective control only if they are hung where cattle are forced to dust. Backrubbers can also give control but are usually less successful on horn flies.

Sprays may also be used for horn fly control. Residual sprays are to be applied at 1-2 qt/animal at 150 to 200 psi to gain complete coverage of the animal and penetration to the skin. Treat animals in small groups so that all animals are covered. Feed additives may be used for larval control; however, adult populations may not be affected because of fly migration.

Face flies

Face flies are a major vector for animal-to-animal transfer of the infectious agents of pinkeye. They feed on eye secretions from infected animals and transfer the bacteria from animal to animal.

Pinkeye is found in cattle of all ages but primarily young animals. The causative agent is the bacterium Moraxella bovis. Cattle often carry Moraxella bovis but are immune to actual infection and do not show disease. Young animals have low immunity to M. bovis and are the most susceptible. They are usually on pasture where they may not be observed everyday. Pinkeye is spread by direct or indirect contact with infected cattle.

The first clinical sign of pinkeye is excessive tearing of one or both eyes. As the disease progresses, the animal holds the eye partially or tightly closed. If untreated, the cornea (clear surface of the eyeball) becomes inflamed and turns white. The cornea may ulcerate. If ulceration is severe, a permanent scar may form. As healing begins, blood vessels migrate toward the ulcer. A white scar may remain in the center of the affected eye. The scar may resolve over time. The disease course is usually four to eight weeks. Damage to the affected eye may result in permanent blindness. The animal may refuse to nurse, graze or drink because of pain and/or blindness. Affected calves often lose weight. Reduced weaning weight is common. In addition to treatment and labor, this is a major cost of pinkeye. Injury of the eye must be differentiated from infectious causes. Careful examination of the eye is necessary to determine if injury has occurred.

Pinkeye prevention is more rewarding and cost-effective than treatment. Good face fly control is an important part of most pinkeye-control programs. Fly control should include different strategies throughout the summer. Some producers utilize insecticide ear tags. Rotating the type of insecticide from year to year is advised. Most fly tags last for approximately five months but lose effectiveness over time. Poor fly control may result in late summer if tags are inserted too early in the year. Insecticide dust bags or “face mops” are helpful but must be placed where animals will contact them on a daily basis. Fencing off watering tanks or salt/mineral feeders so that cattle must pass through a dust bag is one way. Sprays can be used, but cattle must be gathered up and sprayed on a regular basis for good control.

Prevention and control of pinkeye is of major importance in producing a quality product. Pinkeye normally does not cause high mortality but can cause severe economic losses to the cattle industry due to market discounts, reduced feed efficiency and weight loss. Market discounts may be $50 per head or more. A blind calf is difficult to handle and can result in carcass damage.

Treating pinkeye increases the risk of drug residues and carcass blemishes. Most pharmaceuticals used in treatment are irritating to muscle tissue. Make sure the volume at each injection site is no more than 10 ml. All injections, including pinkeye vaccination, should be anterior to the shoulder blade minimal. Follow label directions when treating pinkeye.