Horse owners and caretakers have a responsibility for the horses in their care. They must protect their animals from diseases and parasites. The information given here on diseases and parasites is intended only as a guide for horse owners. It is not intended to be used in lieu of the services of a veterinarian. At the first sign of illness in their horses, owners should call a veterinarian for diagnosis and treatment.

General Health Program

A strict program of sanitation, disease prevention, and parasite control is necessary to protect the health of horses. Although the exact program will vary from farm to farm, the basic principles are the same. A horseman may compare the following general program with his existing program and use it to develop similar and more specific programs.

(1) Avoid public feeding and watering facilities.

(2) Read the sections that discuss the diseases and parasites of horses; become familiar with symptoms and treatments.

(3) When signs of infectious disease appear, isolate affected animals promptly, provide them with separate water and feed containers, and follow the instructions and prescribed treatment of a veterinarian.

(4) Prevent or control parasites by adhering to the following program:

(a) Provide good sanitation and a high level of nutrition.

(b) Have adequate acreage. Use temporary seeded pasture rather than permanent pasture, and practice rotation grazing.

(c) Pasture young animals on clean pastures. Never allow them to graze on an infested area unless the area has been either plowed or left idle for a year.

(d) Do not spread fresh horse manure on pastures grazed by horses. Either store the manure in a suitable pit for at least 2 weeks or spread it on fields that are to be plowed and cropped.

(e) When small pastures or paddocks must be used, pick up droppings at frequent intervals.

(f) Keep pastures mowed and harrowed. Use a chain harrow.

(g) Prevent fecal contamination of feed and water.

(h) Administer suitable vermifuges when internal parasites are present. The choice of vermifuges and administration of them should be by a veterinarian. Later move horses to a clean area.

(i) Apply the proper insecticide when external parasites are present.

(j) If cattle are on the farm, alternate the use of pastures between cattle and horses because horse parasites die in cattle.

(k) Avoid overgrazing because more parasites are present on the bottom inch of grass.

(l) As a disease preventive measure, arrange a scheduled yearly vaccination program with your veterinarian.

Health Program for Breeding and Foaling

(1) Mate only healthy mares to healthy stallions and observe scrupulous cleanliness at the time of service and examination. Never breed a mare that has any kind of discharge.

(2) Provide plenty of exercise for the stallion and pregnant mare in harness, under saddle, or by turning them loose in a large pasture where plenty of shade and water are available.

(3) During spring and fall when the weather is warm, allow the mare to foal in a clean, open pasture away from other livestock. During bad weather, keep the mare in a roomy, well-lighted, well-ventilated box stall that is provided with clean bedding. Before using the stall, thoroughly disinfect it with a lye solution made by adding one can of lye to 12 to 15 gallons of water. After the foal is born, remove all wet, stained, or soiled bedding and dust the floor lightly with lime. Do not use too much lime because it irritates the eyes and nasal passages of foals. When the afterbirth has been completely discharged, it should be buried in lime or burned. The mare should be kept isolated until all discharges have stopped.

(4) To lessen the danger of navel infection, promptly treat the navel cord of the newborn foal with tincture of iodine.

(5) As a precaution against foaling diseases and other infections, a veterinarian may administer antibiotics to both the mare and foal on the day of foaling.

Health Program for New Horses and Visiting Mares

(1) Isolate new animals for 3 weeks before adding them to the herd. During this period, a veterinarian may administer sleeping sickness vaccine in season and tetanus toxoid, make a thorough general and parasitic examination, make a genital examination of breeding animals, and treat animals when necessary.

(2) Make sure that mares brought in for breeding are accompanied by a health certificate issued by a veterinarian. Closely watch mares that have had trouble foaling or have lost foals.

(3) If possible, saddle, bridle, or harness visiting mares near their own isolation quarters and use tack and equipment that is not used by mares kept on the establishment.

Diseases of Horses

The following summary of diseases is intended only to supplement the services of a veterinarian to help provide more rapid detection of trouble, and to improve nursing care for sick horses.

(1) Anthrax (splenic fever, charbon).—An acute, infectious disease caused by Bacillus anthracis, a large, rod-shaped organism.

Symptoms.—This disease has a history of sudden deaths. Sick animals are feverish, excitable, and later depressed. They carry the head low, lag behind the herd, and breathe rapidly. Swellings appear over the body and around the neck region. Milk secretion may turn bloody or stop entirely, and there may be a bloody discharge from all body openings.

Treatment.—Isolate all sick animals. At the first sign of any of the above symptoms, a veterinarian should be called at once. The veterinarian may give large quantities of antibiotic (3 to 12 million units of penicillin). In the early stages of the disease, 50 to 100 milliliters (ml.) of antianthrax serum may also be helpful. Provide good nursing care.

Control.—Quarantine infected herds. All carcasses and contaminated material should be burned completely or buried deeply and covered with quicklime, preferably on the spot. Vaccinate all exposed but healthy animals, rotate pastures, and initiate a rigid sanitation program. Spray sick and healthy animals with an insecticide to avoid fly transmission of the infection.

Prevention.—In infected areas, vaccination should be repeated each year, usually in the spring. Provide fly control by spraying animals during the insect season.

Discussion.—The disease is general throughout the world in so-called anthrax districts. Cattle are more susceptible to anthrax than horses. A farmer or rancher should never open the carcass of a dead animal suspected of having died from anthrax. Instead, a veterinarian should be summoned at the first sign of an outbreak. Control measures should be carried out under the supervision of a veterinarian. The bacillus that causes anthrax can survive for years in a spore stage, resisting all destructive agents.

(2) Distemper (strangles).—A widespread contagious disease caused by Streptococcus equi, a bacterium.

Symptoms.—Sick animals show depression, loss of appetite, high fever, and a discharge from the nose. By the third or fourth day of the disease, the glands under the jaw start to enlarge, become sensitive, and eventually break open and discharge pus. A cough is present.

Treatment.—Good nursing is the most important treatment. This includes clean, fresh water, good feed, uniform temperature, and shelter away from drafts. A veterinarian may prescribe one of the sulfas or antibiotics, or both.

Control.—Put affected animals in strict quarantine. Clean and disinfect contaminated quarters and premises.

Prevention.—Prevention consists of avoiding contact with infected animals or contaminated feeds, premises, and equipment. The injection of animals with bacterin containing killed Streptococcus equi will help raise the level of immunity and may prevent the disease. However, the use of bacterins is not always beneficial.

Discussion.—The disease is worldwide and it attacks animals of any age, but it is most common in young stock. Death losses are low. Affected animals are usually immune for the remainder of life.

(3) Encephalomyelitis (sleeping sickness).—A virus, epizootic (epidemic) disease that may be carried by birds and mosquitoes. It is caused by four different viruses. The two most common ones are known as the eastern type and the western type.

Symptoms.—In early stages, animals walk aimlessly about, crashing into objects. Later they may appear sleepy and stand with a lowered head. Grinding of the teeth, inability to swallow, paralysis of the lips, and blindness may be noted. Paralysis may cause animals to fall. If affected animals do not recover, death occurs in 2 to 4 days.

Treatment.—Careful nursing is perhaps the most important treatment. Serum treatment is sometimes effective when given very early in the disease. A veterinarian should be consulted about this.

Control.—Control measures include prompt disposal of all infected carcasses; destruction, if possible, of insect breeding grounds; and as little movement as possible of animals from an epizootic area to a clean one.

Prevention.—Vaccinate all animals before May of each year or as soon as the disease makes its appearance in a community.

Discussion.—The disease is widespread. Since 1930, nearly a million horses and mules have been affected in the United States. Some animals make full recovery but other survivors do not. The mortality rate in the western type is about 30 percent, but in the eastern type it is 90 percent or higher. Birds and wild rodents are natural disease hosts for the western type. Mosquitoes (Culex tarsalis) transmit the disease.

(4) Equine abortion (premature expulsion of the fetus).—The causes of abortion may be grouped under five headings as follows:

(a) Salmonella abortivoequina abortion occurs most frequently in the last half of pregnancy.

(b) Streptococcic abortion usually occurs early in pregnancy—prior to the fifth month.

(c) Virus, or epizootic abortion (rhinopneumonitis), generally occurs late in pregnancy—after the fifth month. Some foals are born alive and die at 2 to 3 days of age.

(d) Viral arteritis is caused by a virus. It produces fever, inflammation of the mucosa in the respiratory tract, and edema of the eyelids and legs. As many as 50 to 80 percent of pregnant mares may abort.

(e) Miscellaneous causes of abortion may be due to such things as accidents, faulty feeds, or twins.

Treatment.—Quarantine animals that have aborted and give them good feed and care.

Control.—Burn or bury the bedding and fetus of mares that have aborted. Disinfect contaminated premises. Isolate newly introduced animals to the farm.

Prevention.—Prevent abortion caused by Salmonella abortivoequina by vaccinating all pregnant mares with a bacterin every year where premises are infected with the organism.

Prevent streptococcic abortion by mating only healthy animals and observing scrupulous cleanliness at mating.

Prevent rhinopneumonitis by intranasal inoculation with hamster-adapted virus. Inoculate all horses of both sexes and all ages in July and October of each year.

Prevent viral arteritis by isolating new horses to the farm and quarantining affected animals. No vaccines are available for immunization.

Discussion.—It is estimated that for the United States as a whole, one-half of all pregnant mares either abort or produce weak foals. Sanitation and herd health are important factors in lessening the number of abortions regardless of kind. Consult a veterinarian whenever abortion occurs. Cattle abortion on the premises will not affect pregnant mares and cause them to abort.

(5) Equine infectious anemia (swamp fever).—An infectious virus disease.

Symptoms.—Symptoms of the disease vary, but usually they include some of the following: high and intermittent fever; depression; stiffness and weakness, especially in the hindquarters; anemia; jaundice; edema and swelling of the lower body and legs; unthriftiness; and loss of condition and weight, even though the appetite is good. Most affected animals die within 2 to 4 weeks.

Treatment.—No successful treatment is known.

Control.—Segregate infected animals and have them use separate feeding and watering facilities. Kill sick animals and burn or bury their carcasses.

Prevention.—Use disposable hypodermic needles when horses are vaccinated against disease and sterilize all other skin penetrating instruments by boiling them at least 15 minutes after each use. Practice good sanitation and eliminate or reduce biting insects as much as possible. Watch for sick horses and get a diagnosis by a veterinarian if any are observed. Use separate tack equipment on each horse. Keep stalls, starting gates, and other facilities clean at racetracks and shows. This disease has existed in different sections of the United States for at least 50 years but no preventive vaccination is known.

Discussion.—Infected horses may be virus carriers for years and are a danger to susceptible horses.

(6) Equine influenza.—An infectious disease caused by a myxovirus that has properties of the Type A influenza viruses.

Symptoms.—Young animals, except for very young foals that have immunity from the dam's milk, are particularly susceptible. Older animals are usually immune. Symptoms develop 2 to 10 days after exposure. The onset of the disease is marked by a. rapidly rising temperature that may reach 106° F. and persist for 2 to 10 days. Other symptoms include loss of appetite, extreme weakness and depression, rapid breathing, a dry cough, and a watery discharge from the eyes and nostrils that is followed by a white to yellow nasal discharge.

Treatment.—Treatment should be handled by a veterinarian. Avoid exercising the animals during the period of elevated temperature. The use of antibiotics and/or sulfa drugs may prevent some of the complicated secondary conditions.

Control.—Avoid transmission of the virus on contaminated feed, bedding, water, buckets, brooms, clothing and hands of attendants, and transportation facilities.

Prevention.—Vaccinate with a killed virus. Use two doses; follow the manufacturer's directions on the time of the second dose. Also, give each animal an annual booster shot, or a booster when animals are exposed or when an epidemic occurs. Quarantine sick animals, and isolate all new animals to the premises for 3 weeks.

Discussion.—The disease is widespread throughout the world. It frequently appears where a number of horses are assembled, such as racetracks, sales, and shows. The death rate is low but economic loss is high. The disease interrupts training, racing, and showing schedules and it may force the withdrawal of animals from sales. Although horses, swine, and humans are subject to influenza and the symptoms are similar for each, there appears to be no transmission of the disease between any of them.

(7) Glanders (farcy).—An acute or chronic infectious disease caused by Malleomyces mallei, a bacterium.

Symptoms.—The chronic form most often attacks horses, affecting the lungs, skin, or nasal passages. There may be a nasal discharge that later becomes pus, and nodules and ulcers may appear in the skin. With the lung type, there generally is loss in condition, lack of endurance, bleeding and a mucus discharge from the nose, and coughing. The skin of the extremities may develop ulcers that exude a honeylike tenacious discharge.

The acute form more often attacks mules and donkeys. The symptoms are similar to the chronic form, but more severe. Death usually occurs in a week.

Treatment.—No cure is known.

Control.—Use the mallein test to detect infected animals or animals suspected of having the disease. Destroy infected animals and clean and disinfect contaminated equipment and premises.

Prevention.—Avoid inhalation or ingestion of the causative organism. Do not use public watering places.

Discussion.—Glanders is prevalent in areas where horses still are used for transportation and work. The disease has largely disappeared from the mechanized areas of the world, including the United States, but it is not eradicated. Through the transport of animals, glanders can make its appearance anytime in any area.

(8) Naval infection (joint ill, navel ill, actinobaccillosis, streptococcus). An infectious disease of newborn animals caused by several kinds of bacteria.

Symptoms.—Infected animals have loss of appetite; swelling, soreness, and stiffness in the joints; general listlessness; and umbilical swelling and discharge.

Treatment.—A veterinarian may give a blood transfusion from the dam to the offspring, or he may administer a sulfa, an antibiotic, a serum, or a bacterin.

Control.—See prevention.

Prevention.—Practice good sanitation and hygiene at mating and parturition. Feed iodized salt to pregnant mares in iodine-deficient areas. Soon after birth, treat the navel cord of newborn animals with tincture of iodine.

Discussion.—The disease appears throughout the United States. About 50 percent of infected foals die and many that survive have deformed joints. Providing clean quarters for the newborn and painting the navel cord with tincture of iodine are the best preventive measures.

(9) Tetanus (lockjaw).—Chiefly a wound-infection disease caused by a powerful toxin, more than 100 times as toxic as strychnine, that is liberated by the bacterium Clostridium tetani, an anaerobe.

Symptoms.—This disease usually is associated with a wound. First sign of tetanus is a stiffness about the head. Animals often chew slowly and weakly and swallow awkwardly. The third or inner eyelid protrudes over the forward surface of the eyeball. The slightest noise or movement causes sick animals to have violent spasms. Usually sick animals remain standing until close to death. All ages are susceptible.

Treatment.—Place sick animals under the care of a veterinarian and keep them quiet. Good nursing is important. If given early in the disease, massive doses of antitoxin, 100,000 to 200,000 units or more, may be effective. Also, tranquilizers will reduce the extent and severity of muscular spasms, and antibiotics will help.

Control.—See prevention.

Prevention.—Under the direction of a veterinarian, give tetanus toxoid in two doses at 6-week intervals, followed by a booster injection annually. If premises pre unsanitary, all surgery should be accompanied with tetanus antitoxin.

Discussion.—Tetanus is worldwide, but in the United States it occurs most frequently in the South. Death occurs in over half of the affected cases.

(10) Vesicular stomatitis.—A contagious disease of the mouth caused by a virus.

Symptoms.—Blisters and rawness appear mainly on the tongue but also, on the inner surfaces of the lips, angles of the mouth, and the gums. There is considerable salivation. Symptoms appear in 2 to 5 days after exposure.

Treatment.—Make the animal as comfortable as possible and provide plenty of water and soft feed.

Control.—None.

Prevention.—None. No vaccination is available.

Discussion.—The disease may affect 50 percent of the animals on the premises.

Parasites of Horses

Parasites live in or on the bodies of host animals. Parasites kill some horses but the main damage is lowered efficiency. Attacks are insidious and cause damage before it is noticed.

Internal parasites

Some 150 different kinds of internal parasites attack horses throughout, the world and probably no animal is ever entirely free of them.

Parasites may be located in practically every tissue and cavity of the body. However, most of them are in the alimentary tract, lungs, body cavity, or bloodstream. Those in the digestive system usually become localized there, but others travel throughout different parts of the body.

The general symptoms of parasitic infection in horses are weakness, unthriftiness, emaciation, tucked-up flanks, distended abdomen, rough coat, pale membranes in the eyes and mouth, stunted growth in young animals, and in some cases frequent colic and diarrhea. Affected animals usually eat well and the temperature remains normal. But an infected animal always loses some efficiency as a working unit.

Few treatments with only one drug are effective in removing bots and various gastrointestinal worms from horses. Usually, it is necessary to use a combination of drugs. For this purpose, the specific combination is dependent upon the kinds of parasites present in the horses to be treated. It is always wise, therefore, to obtain a definite diagnosis from a veterinarian or veterinary diagnostic laboratory before treatment is given. A veterinarian should always be consulted for safe and effective dosages of the various drugs and treatment schedules.

The common internal parasites of horses and some of the drugs used to treat them are as follows:

Parasites in the stomach

(1) Stomach worms (Habronema spp., Trichostrongylus axei).—A group of parasitic worms that produces inflammation of the stomach.

Symptoms.—Horses suffer loss of condition and severe gastritis. Sometimes, the larvae of large stomach worms are partially responsible for the skin disease of horses called summer sores.

Treatment.—Probably the best drug to use for Habronema spp. is carbon disulfide. Dosage and administration should be determined by a veterinarian. No drugs have been tested adequately against Trichostrongylus axei, the small stomach worm.

Prevention and control.—Provide good sanitation, proper manure disposal, and fly control.

Discussion.—Stomach worms attack horses throughout the United States. Wasted feed and lowered efficiency are the chief losses.

(2) Bots (Gasterophilus spp.).—Four species of bots have been found in the United States but only three are serious pests of horses.

Symptoms.—Animals attacked by the botfly may toss their heads in the air, strike the ground with their front feet, and rub their noses on each other or any convenient object. Animals infected with bots may show frequent digestive upsets and even colic, lowered vitality and emaciation, and reduced work output. Bots may penetrate the stomach wall and cause death.

Treatment.—Use of carbon disulfide, trichlorfon, or dichlorvos under the direction of a veterinarian is recommended.

Prevention and control.—Frequent grooming, washing, and clipping help prevent bot attacks. Prevention of reinfection is best assured through community campaigns in which all horses within the area are treated. Fly nets and nose covers offer some relief from the attacks of botflies.

Discussion.—Bots are worldwide. The presence of bots results in loss of feed to feeding worms, itching and loss of tail hair from rubbing, lowered work efficiency, retarded growth of young animals, lowered breeding efficiency, and death in severe infections.

Parasites in the small intestine

(1) Large roundworms or ascarids (Parascaris equorum).—The female varies from 6 to 22 inches long and the male from 5 to 13 inches. When full grown, both are about the diameter of a lead pencil.

Symptoms.—The injury caused by ascarids ranges from light infections producing moderate effects to heavy infections that may cause death. Death usually is due to a ruptured intestine. Serious lung damage caused by migrating ascarid larvae may result in pneumonia. More common are retarded growth and development manifested by a potbelly, rough hair coat, and digestive disturbances. Ascarids affect foals and young animals, but rarely affect horses over 5 years old; older animals develop immunity from early infections.

Treatment.—Veterinarians most commonly use one of the following compounds for the treatment of this parasite: carbon disulfide, piperazine compounds, trichlorfon, dichlorvos, or thiabendazole.

Prevention and control.—Keep the foaling barn and paddocks clean, store manure in a pit 2 to 3 weeks, provide clean feed and water, and place young foals on clean pasture.

Discussion.—Ascarids attack horses throughout the United States. The presence of ascarids results in loss of feed to feeding worms, lowered work efficiency, retarded growth in young animals, lowered breeding efficiency, and death in severe infections.

(2) Threadworm (Strongyloides westeri).—Threadworms are also known as strongyloides.

Symptoms.—Threadworms attack foals, causing diarrhea. The worms disappear by the time foals are 6 months old.

Prevention and control.—Provide good sanitation and clean, dry bedding.

Discussion.—These worms are common where there is a concentration of foals. Losses are primarily in stunted growth and unthriftiness.

(3) Tapeworms (Anoplocephala magna, A. perfoliata, Paranoplocephala mamillana).—Anoplocephala perfoliata is the most common and most damaging.

Symptoms.—Heavy infections may cause digestive disturbances, loss in weight, and anemia.

Treatment.—Traditional treatments are areca nut, kamala, and oleoresin of male fern; no modern effective drugs have been developed for treatment of tapeworm infections in horses.

Prevention and control.—Provide good sanitation and husbandry, proper manure disposal, and clean bedding.

Discussion.—Tapeworms attack horses throughout the northern part of the United States. Losses are primarily in wasted feed and retarded growth.

Parasites in the large intestine

(1) Large and small strongyles (Strongylus spp. and others).—There are about 60 species of strongyles. Three are large worms that grow up to 2 inches long. The rest are small and some are barely visible to the eye. Large strongyles are variously called bloodworms (Strongylus vulgaris), palisade worms, sclerostomes, and red worms.

Symptoms.—Infected horses have lack of appetite, anemia, progressive emaciation, a rough hair coat, sunken eyes, digestive disturbances including colic, a tucked-up appearance, and sometimes posterior paralysis and death. Collectively these symptoms indicate the disease known as strongylosis. Harmful effects are greatest in young animals. One species of large strongyles (Strongylus vulgaris) may permanently damage the intestinal blood vessel wall and cause death at any age.

Treatment.—Use thiabendazole; phenothiazine + piperazine; phenothiazine + piperazine-1-carbodithioic acid; dithiazanine + piperazine; trichlorfon; or dichlorvos. The decision as to which drugs to use and the dosage level should be made by a veterinarian.

Prevention and control.—Gather manure daily from pastures and barns and store it in a pit 2 to 3 weeks. Rotate pastures and avoid moist pasture and overstocking.

Discussion.—Strongyles attack horses throughout the United States wherever horses are pastured. Attacks of strongyles result in loss of feed to feeding worms, lowered work efficiency, retarded growth of young animals, lowered breeding efficiency, and death in severe infections.

(2) Pinworms (Oxyuris equi, Probstmyria vivipara).—Two species of pinworms, or rectal worms, frequently are found in horses. Oxyuris equi are whitish worms with long, slender tails. Probstmyria vivipara are so small they are scarcely visible to the eye.

Symptoms.—The symptoms are irritation of the anus and tail rubbing. Heavy infections also may cause digestive disturbances and anemia. Large pinworms are most damaging to horses and may be seen in the feces of heavily infected animals.

Treatment.—The common drugs are thiabendazole, trichlorfon, or dichlorvos or various combinations of trichlorfon, phenothiazine, piperazine, and thiabendazole. Which drugs to give and dosage should be determined by a veterinarian.

Prevention and control.—Provide good sanitation and keep animals separated from their own excrement.

Discussion.—Pinworms attack horses throughout the United States.

Parasites in the lungs

(1) Lungworms (Dictyocaulus arnfieldi).—The equine lungworm is very rare in the United States.

Symptoms.—Donkeys seem to be able to carry large numbers of lungworms without showing any symptoms. They develop a tolerance. However, infected foals may become unthrifty and develop a cough. There is a rise in temperature with lungworm infection.

Prevention and control.—Where lung-worm infection is suspected, a fecal examination should be made. Infected burros should be kept away from foals.

Discussion.—Lungworms may be found in the air passages of the horse and other equines. The male worm reaches a length of about 1 inch and the female may be about 2 inches long. The eggs are laid in the lungs and pass out of the horse's body through the intestine. They hatch into first-stage larvae that develop eventually into the third, or infective, stage. The infective larvae enter the body through the mouth, travel in the lymph vessels to the thoracic duct, then to the heart, and eventually to the lungs.

Blood protozoan parasites

(1) Equine piroplasmosis (babesiasis).—Caused by Babesia caballi or B. equi, protozoan parasites that invade the red blood cells.

Symptoms.—Equine piroplasmosis is similar to equine infectious anemia but a positive diagnosis can be made by determining whether or not protozoa are in the red blood cells. Symptoms include a fever of 103° to 106° F., anemia, jaundice, depression, thirst, a discharge from the eyes, and swelling of the eyelids. Constipation and colic may occur and the urine is a yellow to reddish color. Symptoms appear 1 to 3 weeks after exposure.

Treatment.—A number of treatments are used but the choice should be left to a veterinarian. Many States have laws that require you to report this infection.

Prevention and control.—Control the ticks that carry the parasites, especially brown dog ticks and tropical horse ticks, both of which are found in the United States. Methods of tick control are discussed in the section on external parasites. Practice rigid sanitation in the use of all syringes, needles, and medical instruments. Recovered animals remain carriers for 10 months to 4 years and should be isolated.

Discussion.—This infection is worldwide. In the United States, it was first diagnosed in Florida in 1961. The death rate is from 10 to 15 percent of infected animals.

External parasites

Several kinds of external parasites attack horses. These pests lower the vitality of horses, damage the hair and skin, and produce a generally unthrifty condition.

External parasites also are responsible for the spread of several serious diseases of horses. Equine piroplasmosis (babesiasis) is transmitted by a tick, Dermacentor nitens. Mosquitoes (Culicidae) are vectors of equine infectious anemia (swamp fever) and equine encephalomyelitis (sleeping sickness).

The common measures used to prevent and control external parasites of horses are practicing good sanitation, good grooming, avoiding a too heavy concentration of horses, and spraying or dusting with insecticides. Flies and lice are the most common external parasites of horses but some of the others can produce more severe injury when they occur.

The common external parasites of horses and approved control measures are as follows:

(1) Blowfly.—The blowfly group consists of several species of flies that breed in animal flesh.

Symptoms.—The maggots of blowflies infest wounds and spread over the body, feeding on the skin surface, producing severe irritation, and destroying the ability of the skin to function. Infested animals rapidly become weak, fevered, and unthrifty.

Treatment.—A 0.25 percent coumaphos (Co-Ral) spray is effective for controlling blowfly larvae infesting soiled hair and wounds.

Prevention and control.—To control the blowfly, destroy dead animals by burning or deep burial and by using traps, poisoned baits, electrified screens, and repellents.

Discussion.—Blowfly attacks are widespread but they present the greatest problem in the Pacific Northwest, the South, and the Southwest. Death losses are not large but work efficiency is lowered.

(2) House fly and stable fly.—House flies are nonbiting, nuisance insects. Stable flies are biting insects that bite principally on the legs.

Symptoms.—Flies annoy horses, causing them to fight. Horses may strike the ground with their feet, toss their heads, switch their tails, and run.

Treatment.—Treat animals infested with house and stable flies with any of the following insecticides, using the dosages given. Indication is shown if the treatment is also effective against horn flies.

Carbaryl spray, 0.5 percent, 1 quart, not more often than every 4 days. (Also for horn flies.)

Ciodrin spray, 0.15 to 0.3 percent, 1 quart, not more often than every 7 days. (Also for horn flies.)

Ciodrin mist spray, 2 percent in oil, 1 to 2 ounces. (Mist spray is composed of very fine, or minute, droplets.)

Coumaphos spray, 0.06 to 0.25 percent, 1 to 2 quarts, to backs of animals every 3 weeks or as needed. (Also for horn flies.)

Dioxathion spray, 0.15 percent, 1 to 2 quarts, not more often than once every 2 weeks. (Also for horn flies.)

Dichlorvos mist spray, 1 percent in oil, 1 to 2 ounces. (Also for horn flies.)

Malathion spray, 0.5 percent, 2 quarts, to backs every 3 weeks or as needed. (Also for horn flies.)

Methoxychlor spray, 0.5 percent, 1 to 2 quarts, to backs every 3 weeks or as needed. (Also for horn flies.)

Ronnel spray, 0.25 to 0.5 percent, 1 to 2 quarts, to backs every 3 weeks or as needed. (Also for horn flies.)

Pyrethrins and synergist, 1 to 2 quarts when used as a wet spray, or 1 to 2 ounces as a mist spray; repeat every 2 to 3 days as needed. (Wet, or saturating, spray should be applied liberally under pressure to wet the hair coat to the skin.)

The following are effective against house flies but not stable flies: (a) Baits consisting of a 0.5 to 2 percent organophosphate toxicant such as dichlorvos, diazinon, malathion, naled, or trichlorfon mixed with a food attractant such as sugar or sirup; or (b) treated cotton cord impregnated with 10 percent parathion or 25 percent diazinon and suspended from the ceiling.

Prevention and control.—Practice good sanitation, including proper disposal of all fly breeding media such as manure and waste feed. Use screens when practical.

Discussion.—Habronema spp., a roundworm, is transmitted by house flies. Stable flies can carry anthrax, infectious anemia, and surra.

(3) Horn fly.—Horn flies are primarily pests of cattle but they sometimes seriously annoy horses.

Treatment.—Treat infested animals with any of the insecticides recommended for horn flies in the treatment section under "House Fly and Stable Fly."

(4) Horsefly, deerfly, and mosquito.—All of these are biting insects. Bites of horseflies and deerflies are painful.

Treatment.—Use repellent sprays containing 0.05 to 0.1 percent pyrethrins, with or without 0.5 to 0.1 percent synergist. Mists or wet sprays of such formulations will lessen the attacks of biting insects for several hours to a full day. Sprays containing 0.3 percent Ciodrin will provide short-time protection from biting flies and mosquitoes, but do not apply more often than every 7 days.

Prevention and control.—The best method of controlling mosquitoes is to provide drainage or landfill in breeding areas.

Discussion.—Mosquitoes transmit equine encephalomyelitis.

(5) Face fly.—Face flies gather in large numbers on the faces of horses, especially around the eyes and nose.

Treatment.—Use a 0.3 percent Ciodrin spray or brush the forehead lightly with a sirup bait containing 0.5 percent dichlorvos (Vapona). These two treatments are effective for only a short time and may have to be applied almost daily.

Prevention and control.—Shelters for horses on pastures give some protection.

(6) Lice.—These are small, flattened, wingless insect parasites. Horses are commonly infested by two species of lice; they are the common horse biting louse, Damalinia equi, and the horse sucking louse, Haematopinas asini.

Symptoms.—Symptoms include intense irritation, restlessness, and loss of condition. There may be severe itching and the animal may be seen scratching, rubbing, and gnawing the skin; scabs may be evident and the hair may be rough, thin, and without luster. Lice are likely to be most plentiful around the root of the tail, on the inside of the thighs, over the fetlock region, and along the neck and shoulders.

Treatment.—Treat infested animals with any of the following insecticides: Spray with 0.5 percent carbaryl but do not treat more often than every 4 days; spray with 0.3 percent Ciodrin but do not treat more often than every 7 days; spray with 0.125 percent coumaphos (Co–Ral); spray with 0.15 percent dioxathion (Delnav), but only at 2-week intervals and do not treat foals; or spray with 0.5 percent malathion but do not treat foals under 1 month old. A second application after an interval of 12 to 14 days may be required. Repeated treatments are rarely necessary to control lice.

Prevention and control.—Because of the close contact of horses during the winter, it is practically impossible to keep them from becoming infested with lice. For effective control, all horses should be treated with insecticides simultaneously at intervals as needed, especially in the fall about the time they are placed in winter quarters.

Discussion.—Lice are widespread. They retard growth, lower work efficiency, and produce unthriftiness. They show up most commonly on neglected animals in winter.

(7) Mites.—These are very small parasites that cause mange (scabies, scab, and itch). The two chief forms of mange are sarcoptic mange caused by burrowing mites and psoroptic mange caused by mites that bite the skin and suck the serum and lymph but do not burrow. Mites also may cause chorioptic mange.

Symptoms.—Symptoms are irritation, itching, and scratching. The skin crusts over and becomes thick, tough, and wrinkled. Mange appears to spread most rapidly during the winter months.

Treatment.—Treat animals with sprays containing (a) 0.25 percent coumaphos, (b) 0.1 to 0.3 percent Ciodrin, or (c) 0.5 percent malathion; give two treatments 10 to 14 days apart. Lime-sulfur and nicotine sprays are effective but they are little used on horses today.

Prevention and control.—Keep healthy horses away from diseased animals or infested premises. Spray infested animals with insecticides and quarantine affected herds.

Discussion.—Mites are widespread. They retard growth, lower work efficiency, and produce unthriftiness. When sarcoptic and psoroptic mange appear, they must be reported to State or Federal animal health agencies. Also, in many States, chorioptic mange must be reported.

(8) Ringworm.—This is a contagious infection of the outer layers of skin caused by an infestation of microscopic fungi.

Symptoms.—Round, scaly areas almost devoid of hair appear mainly in the vicinity of eyes, ears, side of the neck, or root of the tail. Mild itching usually accompanies the infection.

Treatment.—Clip the hair from the infected skin areas. Soften skin crusts with warm soap and water and remove them if desired. Let infected areas dry and then paint them with weak tincture of iodine every 3 days or treat them with a mixture of one part salicylic acid and 10 parts alcohol every 3 days until the infection clears up.

Prevention and control.—Isolate infected animals. Disinfect everything that has been in contact with infected animals, including curry combs and brushes. Practice strict sanitation.

Discussion.—Ringworm attacks horses throughout the United States, primarily as a stable infection. It is unsightly and infected animals may have considerable discomfort, but economic losses are low.

(9) Screwworm.—Maggots of the screwworm fly require living flesh of animals on which to feed.

Symptoms.—Symptoms include loss of appetite, unthriftiness, and lowered activity.

Treatment.—Use ronnel smear. Brush or smear the infected area twice the first week and then weekly until healed. A wash containing 0.25 coumaphos also is effective.

Prevention and control.—Area-wide screwworm eradication by sterilizing pupalstage screwworms with X-rays or gamma rays has been most effective. Try to keep animals from wounding themselves and protect any wounds that do occur. Schedule castrations in winter when flies are least numerous and active.

Discussion.—Screwworm appears mostly in the South and Southwest where it may cause 50 percent of the normal annual livestock losses. The screwworm has been eradicated from the Southern United States east of the Mississippi River.

(10) Ticks.—Several kinds may be found on horses. The most common ones are the winter tick, Dermacentor albipictus; the lone star tick, Amblyomma americanum; and the spinose ear tick, Otobius megnini.

Symptoms.—The symptoms are lowered vitality and itching; animals rub and scratch infested parts.

Treatment.—To control winter and lone star ticks, use the same treatments that are used for lice. For the control of spinose ear ticks, apply a 5 percent coumaphos dust inside the ears, or spray inside the ears with an aerosol bomb containing 2.5 percent ronnel. Repeat treatments as necessary.

Prevention and control.—Treatment with insecticides will control ticks on horses and protect them against reinfestation for several weeks.

Discussion.—Ticks appear mostly in the South and West. They reduce vitality of horses and may spread piroplasmosis and African horsesickness.

M. E. Ensminger

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