Thread-necked worms
Thread-necked worms, Nematodirus helvetianus, are found throughout the United States. They in-habit the upper one-third of the small intestine. Damage is created when the parasite tunnels into the intestinal mucosa, absorbing protein and blood.

Trichuris
Infections caused by species of the Trichuris parasite (whip worms) affect primarily calves and yearlings. Trichuris eggs are very climate-tolerant and are likely to persist on problem premises.

The numbers of infective Trichuris worms are seldom large, and signs of disease are rarely seen. Thus, the effects of Trichuris infection are apt to be subclinical. In occasional heavy infections, dark feces, poor appetite and anemia may be seen.

Lungworms
Infections by lungworms, Dictyocalus viviparus, are seen most often in temperate climates. Larvae are ingested through grazing.

From the intestines, lungworm larvae migrate to the lungs via the lymphatic system and the arterial blood supply. Larvae emerge into the alveoli and migrate to the bronchioles and bronchi where they mature. The irritation caused by lungworms increases the secretion of fluids, which can lead to congestion or even emphysema and pneumonia.

Cattle of all ages can be affected. Older animals may acquire a degree of immunity from naturally occurring infections. Affected cattle show signs of lungworm disease ranging from moderate coughing to severe, persistent coughing. Some animals experience respiratory distress and even failure. Economic effects of this disease include weight loss and loss
of milk production.

Liver flukes
Fluke disease in U.S. cattle is caused by the trematode Fasciola hepatica.

F. hepatica eggs are passed in the feces of cattle. After hatching in water, the eggs infect lymnaeid snails, where development and multiplication occurs. After two months or longer, depending on temperature, an advanced stage of F. hepatica encyst on aquatic vegetation, from which they are ingested by cattle.

Following ingestion, young flukes are released in the duodenum, penetrate the intestinal wall and enter the peritoneal cavity. Then they penetrate the liver capsule and spend several weeks growing and destroying tissue before entering the bile ducts to mature and produce eggs. Two to three months usually elapse from ingestion to shedding of eggs in the feces. Most adult flukes are shed by cattle within five to six months.

When tissue damage occurs in the liver, adjacent clostridial spores may vegetate and release fatal toxins.

Control of liver flukes should include both repression of the snail population and treatment of susceptible animals.

External parasites
Investing in control measures for external parasites can be as profitable as controlling internal parasites. Just 200 horn flies on a cow, calf or yearling is the threshold level for economic losses. Horn fly counts of 20,000 per animal have been reported, and annual losses to this fly alone have been estimated to exceed $700 million.

Other flying insects, including face flies, stable flies, heel flies, screw worm flies, horse flies, deer flies and gnats, increase production losses to well over $1 billion per year.

With industrywide losses being this great, investments in fly control can be very profitable.

Cattle are commonly seen stamping their feet, switching their tails, throwing their heads and rubbing on objects to rid themselves of discomforting flies. These actions consume energy that would otherwise go into production. When effective fly control is practiced, weight gains in calves often increase 15 to 30 pounds and in yearlings from 20 to nearly 50 pounds. Cows end the grazing season in better shape, winter less expensively and are more apt to breed back the following summer.

Face flies
Face flies, Musca autumnalis, are a pest of cattle throughout the United States, except for the Deep South, Arizona and New Mexico. These flies are slightly larger and similar in appearance to house flies.

Face flies feed on fresh rangeland feces, which generally limits their effect to nonconfined cattle. Cattle confined near pasture may also be infested.

Typical of other species of nonbiting flies, face flies feed on liquid substances. Face flies feed particularly around the eyes, nose and mouth, and are thought to be spreaders of bacterial organisms that cause pink eye. The mouth parts of these flies irritate the eyes, creating an environment suited to bacterial growth. As the eye becomes irritated and begins to weep, it attracts more and more flies, adding to the irritation and opportunity for spread of infection.

Control of face flies is difficult because individual face flies spend relatively little time on the animals and due to problems in applying insecticides to the eyes, face and nose of cattle.

Gnats
Buffalo gnats (Simuliidae), known most commonly as black flies, can be significant pests of cattle, damaging performance and causing disease. These insects are common inhabitants of north temperate and subtropic areas. Black flies are often seen in swarms where strong or swiftly flowing streams provide well-aerated water for larval development. Females require blood for ovarian development.

Another group of biting gnats from the Ceratopogonidae family is a cattle pest. This group includes groups known as midges, sandflies and punkies. Protecting cattle from gnats is very difficult. Most control measures focus on the environment.

Heel flies
Heel flies are the parents of cattle grubs. These robust flies hover and dart around the legs of cattle during the winter in the South, early spring in Central states, and spring through summer in Northern states. They superficially resemble honey bees. They do not feed as adult flies and individuals live for only about a week. Heel flies do not land on cattle, but the females hover close to the heel or leg as they attach eggs to individual hairs on the animal. The ovipositing action apparently tickles the animals and this, along with the buzzing noise made by the flies, causes cattle to run wildly with their tails in the air.

The eggs hatch within a week, tiny larvae crawl down the hair and enter the cow’s skin, and internal migration begins a cycle that will end with large grubs in the animal’s back.

There are two species that look very much alike: Hypoderma lineatum, the common cattle grub, and Hypoderma bovis, the northern cattle grub. Where both species are present, egg laying season occurs two to eight weeks earlier for H. lineatum than for
H. bovis as do all phases of larval development.

Control of adult heel flies is not feasible. (See the section on Grubs.)

Horn flies
A biting insect, horn flies, Haematobia irritans, are a pest of cattle throughout North America. Horn flies are primarily a problem in pastured cattle. Horn fly infestations reduce grazing time and milk production. Cows may lose weight and calf weaning weights may be depressed 15 pounds or more.

Horn flies are about half the size of house flies. They are black in color and appear to be covered with a grayish powder. Horn flies remain on cattle day and night.

Virtually the entire adult life of horn flies is spent on the animal. Females leave the animal body only to deposit eggs. Eggs are deposited on the sides of fresh manure or in the grass or soil beneath it. Eggs hatch in 24 hours or less, and maggots become pupae in four to eight days at temperatures of 75 to 80 degrees. Reaching the pupal stage requires more time at lower temperatures. Flies grow to adulthood while feeding on the manure. They then move to the cattle.

The entire life cycle from egg to adult takes 10 to 14 days.

The life cycle can take two to three weeks under cooler conditions. Reproduction occurs year-round in the southernmost areas of Florida and Texas.

The means for controlling horn flies are broad and highly varied. Special consideration must be given to the resistance horn flies develop to frequently used insecticides.

Horse anddeer flies
Several species (Tabanidae family) of horse (Hybomitra and Tabanus) and deer flies (Chrysops) can be pests of cattle. These biting flies vary in length from one-third to 1 inch. The larvae of most species reproduce in mud or water in streams, lakes and swampy areas.

In the United States, populations of these flies are greatest under the moist conditions of the Southeast. Large outbreaks can occur in upland or dry land areas, however. Control of horse and deer flies is considered by many to be the hardest of the biting-fly group. These flies are intermittent feeders that do not stay on the host for extended periods.

House flies
The nonbiting house flies (Musca domestica) are predominately in or near buildings where there are ample sources of fresh manure and decaying matter. This makes these flies a problem for cattle confined in or around buildings, including those confined in feedyards.

House flies feed on secretions around the eyes, nose, mouth and other moisture on the hair, as well as feedstuffs and animal feces. These practices make house flies a factor in disease transmission and a source of animal annoyance. The life cycle of house flies can be as short as 10 to 14 days under favorable climatic conditions. Sanitation is extremely important in control of these flies. Supplementary use of insecticides can be highly effective.

Stable flies
This light gray and black biting fly is about the same size as a house fly. Its predominant feeding area is the animal’s legs. Stable flies develop in moist, decaying vegetation, such as straw, hay, piles of grass, dead weeds or large round hay bales stored outside. They develop in manure only if it is mixed with hay or straw. This makes stable flies a greater threat to feedyard cattle and cattle quartered in or around buildings.

Control of stable flies is more difficult than horn flies because they feed less often—only once or twice per day for short periods. Sanitary measures that reduce breeding areas are very important.

Screw worm flies
The screw worm fly (Cochliomyia [Callitroga] hominivorax) is now considered to be an eradicated species in the United States but is subject to recurrence. This fly was once a scourge for the North American cattle industry, particularly below the Frost Belt. About twice the size of a house fly, the screw worm fly is bluish-green with three dark stripes on its back.

This fly is attracted to wounds, such as those caused by tick bites, the navels of newborn calves and briar scratches. Eggs are deposited in masses on the fringes of lesions.

Larvae from hatched eggs migrate into the wound and feed on living tissue, using two sharp mouth parts. Infested animals seek deep shade and make frantic efforts to lick or scratch the affected area. Unchecked infestations can be fatal. After maturing in the wound, screw worm larvae drop to the ground, pupate, and shortly emerge as flies to reinfest the old wounds or find new ones.

Ticks
Ticks are bloodsucking external parasites that afflict cattle throughout the world. They adversely affect the economic performance of cattle through blood loss, discomfort, hide damage, and secondary infection of tick bite lesions. Boophilus ticks in the South transmit bovine piroplasmosis (cattle fever). After many years of a vigorous USDA project with rancher cooperation, Boophilus ticks are now a problem in the United States only along a narrow frontier of the Texas-Mexico border.

Ticks are reservoirs as well as transmitters of anaplasmosis. Rocky Mountain wood ticks, especially in the northern Rockies, have been known to kill cattle by causing tick paralysis.

Different species of ticks occur in different parts of the country. In any one location, from one to six species may be significant pests on cattle. A few of the more important ticks on cattle are discussed here.

The winter tick is present throughout the United States but is more commonly a serious pest in Northern states and mountainous areas. Lone star ticks are important cattle parasites from southeastern Texas to northeastern Kansas and eastward through the southern half of the country. Blacklegged ticks are pests of cattle throughout the same region as well as in Northeastern and North Central states.

The Rocky Mountain wood tick is predominant in the Rockies. A large "soft tick," the pajarello, is problematic in California hill country. East of the Rocky Mountains, the American dog tick is always a part of the mixture of species found on cattle. Two species of ticks almost exclusively invade the ears of cattle and other large mammals and cause ear deformation, infection and reduced performance. They are the Gulf Coast tick of Gulf Coast and South Central states, and the spinose ear tick (a "soft tick") of arid regions in the Southwest, the High Plains, and southern parts of the Great Basin.

The life cycle of most ticks is one to two years, but Boophi-lus ticks require as little as 40 days under favorable conditions. Ticks are classified as one-host, two-host, or three-host ticks, according to how many different hosts are used between egg hatching and adult feeding.

Boophilus ticks, winter ticks and spinose ear ticks are one-host ticks. Once the larvae find a host, they stay on the same animal until they have become adults and taken one final meal of blood. All the other ticks mentioned above are three-host species.

The generalized life cycle of three-host ticks:

• larvae hatch from eggs laid on the ground;
• larvae attach to host A (typically a rodent or other small mammal);
• engorged larvae drop to the ground, molt, and become nymphs;
• nymphs attach to host B and engorge with blood (nymphs typically parasitize small- and medium- sized animals, occasionally large animals);
• engorged nymphs drop to the ground, molt and become adult males and females;
• males and females attach to host C and mate (adults parasitize all sizes of animals);
• engorged females drop to the ground and, depending on species, lay from 2,000 to 11,000 eggs apiece, then die.

Short term remediation of ticks requires chemical (acaricidal) control of all life stages on the animal while leaving residual acaricide on the hair coat to prevent reinfestation for several days. Effective treatments vary for different tick species, but methods include dipping, spraying and use of certain ear tags. Pour-ons, dusts, and backrubs may aid in controlling some species.

Long-term reduction of tick populations in pastures include cultural or habitat management that varies regionally. These methods include pasture burning, brush control and long-term pasture rest and rotation. No acaricides are approved for application to pasture and range for tick control, but waste land and recreational areas may be treated.

Grubs
Cattle grubs are probably second only to horn flies in total losses caused to the American beef industry. Grub infestation is the consequence of eggs attached to the hair of cattle at the beginning of the fly season by Hypoderma species (see Heel flies). After the eggs hatch in three to seven days, first-stage larvae crawl down the hair, penetrating the skin, and begin a migratory journey.

The grub larvae’s migratory journey pauses after two to four months, at the esophageal wall for H. lineatum or in the spinal canal for H. bovis, before proceeding to the host’s back. The larvae pass through their second and third stages (warble stage) in the tissue beneath the skin of the back, where they make breathing holes through the skin. After four to six weeks of rapid growth, the third-stage larvae emerge through the breathing holes, fall to the ground and pupate. Depending on weather conditions, adult flies emerge from the pupae in one to three months, ending a one-year life cycle.

Larvae first appear in the backs of cattle about mid-September in the Southern states and late January or later in northern latitudes. Grubs emerge from the backs in November in Texas and during the first half of March in Montana.

Effective treatment of cattle requires systemic insecticides applied as pour-ons, an injection or sprays. Cattle should be treated after heel-fly season but about three months before the anticipated first appearance of grubs in the animals’ backs. Treatment during the final two or three months of larval migration kills the grubs while they are in the esophageal tissue or the spinal canal. Their death results in a localized immune response, which causes tissue swelling, resulting in choking and bloat or paralysis respectively.

Lice
Both biting and sucking lice infest cattle, with biting lice (Damalinia [Bovicola] bovis) being the most common and sucking lice (Haematopinus eurysternus, Linognathus vituli, Solenopotes capillatus), the most damaging.

Both types of lice cause irritation and itching, which prompt cattle to rub and bite infested areas. The incessant crawling and biting or piercing of the skin by sucking lice causes nervousness in infested animals. Sucking lice can extract sufficient blood to lower red-blood-cell counts by 75 percent. Infested cattle may experience reduced appetite, unthriftiness and economic losses. Deaths may occur.

The entire life cycle of the louse occurs on the host animal and requires 20 to 30 days. Eggs laid by females adhere to the hair and hatch in six to 13 days. As nymphs, lice go through three molts within two weeks, becoming egg-laying adults within about five days of the last molt. Dislodged eggs can still hatch and may render premises infective for susceptible animals for up to a week.

Lice infest cattle through out the year. Because the majority are shed in the spring along with the
winter coat, infestations are lowest in summer. Lice populations can explode when winter arrives. Increased bodily contact between animals facilitates the spread of lice, and the winter hair coat increases protection and reproduction.

Effective control of lice with one treatment requires a product that kills both the parasite and its eggs. Because few products available are highly effective against the eggs, two treatments may be required. Pre-winter treatment is important.

Mange mites
Several kinds of mites may live on or in animal skin, causing a disease called mange. Particularly debilitating kinds of mange are called scabies. In cattle there are two types of scabies: sarcoptic scabies caused by the mite species, Sarcoptes scabiei; and psoroptic scabies caused by Psoroptes ovis. Three kinds of cattle mange, usually less severe than scabies, are caused by the mite species Chorioptes bovis, Demodex bovis, and Psorergates bos. They are called chorioptic, demodectic and psorergatic mange, respectively.

Signs of cattle mange and scabies are usually exhibited during late fall and winter. The lesions may heal spontaneously during the summer, but a subclinical infestation persists. The hides of infested cattle are damaged and of poor value at slaughter. Infested animals are often more susceptible to other diseases. Animals infested with sarcoptic or psoroptic scabies may become seriously debilitated.

The life cycles of the mites require 10 to 20 days, depending on conditions and species. All developmental stages (egg, larva or protonymph, deutonymph and adult) occur entirely on the host. Scabies and mange mites spread from animal to animal through close contact. Mites and their eggs are also spread via contact with bedding, trucks, feed bunks and other fomites that have been in contact with infested animals.

Most cattle mange and scabies mites are host-specific, although related varieties infest other domestic and wild mammals. Prevention through management is important. Accurate diagnosis is essential following the emergence of skin diseases, and treatment must be prompt. Sarcoptic and psoroptic scabies are quarantinable; federal and state laws specify treatments and restrict commerce and transportation from infested herds. Some of the other kinds of cattle mange are regulated by state law.

Rats and mice
Rats and mice have been proven to be intermediate hosts for both internal and external parasites. Rodents also cost producers money by eating and spoiling feed and by damaging facilities.

To control rats and mice, experts recommend a three-pronged attack.

• Eliminate breeding and living areas. Clean up to make the environment less inviting.
• Create obstacles to entry. Rats can chew their way in through any hole that starts at 0.5 inch. To keep them out, plug all openings that size or larger with heavy hardware cloth, galvanized sheet metal or reinforced concrete.
• Poison and trap. If trapping, trap heavily and intensively, and put traps within runs or near nesting sites. If poisoning, place poisons at least as close as other available food supplies to nests.

Poisons for mice should be spaced every 6 to 8 feet; for rats, every 25 to 50 feet. When poisoning, remember to think three-dimensionally. Some barn mice live out their lives without ever reaching the floor.

Keep baiting until all signs of feeding have stopped, and check baits often to see if they need replacing. Poison outside as well—every 25 feet around buildings.