Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. Cop: & UNITED STATES DEPARTMENT OF AGRICULTURE CIRCULAR No. 148 R en Va Washington, D. C. Rev ede Parasit ana Parasitic of Horses By Issued November 1930 Revised January 1933 Slightly revised January 1936 | oes Tail ae “ ae oe a { bs | % : : R E C F Sot 4 e | en om ao OR pes acon ae aes BENJAMIN SCHWARTZ Senior Zoologist MARION IMES Senior Veterinarian and WILLARD H. WRIGHT Associate Veterinarian Zoological Division, Bureau of Animal Industry For sale by the Superintendent of Documents, Washington, D.C. CAMEO DOME ES JUL 1 4 1937 a g, Department of Agricultpt Iseases || Price 10 cents Sapitay oe eee wees CIRCULAR No. 148 Issued November 1930; revised January 1933; slightly revised January 1936 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D.C. PARASITES AND PARASITIC DISEASES OF HORSES' By BENJAMIN SCHWARTZ, Senior Zoologist, MARIon IMES, Senior Veterinarian, ‘ and WILLARD H. WricHT, Associate Veterinarian, Zoological Division, Bureau of Animal Industry CONTENTS Page Page Internal parasites of horses.....-....-.----_- 1 | Internal parasites of horses—Continued. Abundance and location_____-_-_----_--__ 1 Misposaliof mantresas see sees esse ee 31 Symptoms and damage produced by Summary of control measures_____.______ 32 DATASET CSE se ete wi a ie is es Ba te 1 | External parasites of horses__________-______- 34 General control measures__________---__- 2 IFLOTSE ICO ws Met A Ne RIS Ey ie ee 34 Medicinal'treatmentie ase 522 oe eee 3 IFLOTVSe Manse se eee ee eee ete 38 IP ROCOZ OD eee ea Rats eee cesta 4 ARKO) 5) HERO aie Ot ean enema TE Tae 45 WOLD AaLasites es ase ee ane eee 5 Treating horses for external parasites__- 48 CO eR rr ys ie Or a et INTERNAL PARASITES OF HORSES? ABUNDANCE AND LOCATION HE TERM PARASITE as used in this circular refers to forms 4 of animal life which, for the purpose of obtaining food and shelter, live on or in the bodies of other animals which are larger than the parasites and are known as hosts. All classes of domesti- cated animals harbor numerous kinds of parasites, and horses, in particular, are liable to infestation not only with many different kinds but also with very large numbers of these pests. A horse’s stomach may contain hundreds of bots, and the small intestine may be packed with large roundworms. The large intestine of the horse is a location especially preferred by parasites, and very often the colon and cecum are found to be teeming with hundreds or thousands of wriggling, parasitic worms, some free in the lumen and others attached to the walls of the gut. Several kinds of worm parasites present in the gut and elsewhere have previously wandered through various parts of the horse’s body before reaching their final locations. In fact, there is hardly an organ or a tissue in the horse which is absolutely free from possible attacks by mature parasites or by their wandering larval forms. SYMPTOMS AND DAMAGE PRODUCED BY PARASITES Parasitic diseases, unlike diseases caused by bacteria, are seldom spectacular in their onset and symptoms and are marked by a slowly 1 This circular supersedes Farmers’ Bulletin No. 1493, Lice, Mange, and Ticks of Horses. * By Benjamin Schwartz and Willard H. Wright. Many of the illustrations in this section of the circular were drawn by Joseph E. Alicata, junior zoologist. 138442 °—37 a 4 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE progressing chain of symptoms which the owner may entirely over- look or confuse with other conditions. The general symptoms of worm infestation in the horse are unthriftiness, weakness, emacia- tion, tucked-up flanks, distended abdomen, rough coat, whitening or bleaching of the mucous membranes (noticed particularly in the mucous lining of the eyelids and mouth), and in some cases frequent eolics and diarrhea. The appetite usually remains good-and the ani- mal shows no rise in temperature. Heavily parasitized animals tire quickly and are frequently unable to stand heavy work. Parasites are particularly damaging to young, growing animals. They attack the foal when it should be making its best growth and produce stunting and lack of development. A considerable part of this damage is a result, no doubt, of the wanderings of the larval worms through various parts of the body of the host before they reach their preferred location where they develop to maturity. While the death rate from parasitic infestation is not high, never- theless these internal pests cause considerable damage. The loss is represented largely by the poor development and stunting of foals, inability of heavily parasitized horses to do a normal amount of work, added costs of feed and maintenance, and loss of working time from verminous colics. The aggregate loss resulting from these con- citions is sufficient to warrant the attention of horse owners to the subject of parasite control. GENERAL CONTROL MEASURES Most parasites of livestock owe their perpetuation to the fact that domestic animals often take their food from the same places they deposit their fecal matter. The eggs of parasites are passed by horses with the manure in stables and on pastures and then go through various stages of development, after which either the eggs or the larval worms reach the interior of the horse with the food and drinking water. Prevention must be directed toward breaking this cycle. Stables and paddocks should be kept in a sanitary condition by the frequent removal of manure. Concrete standings, although objected to by some horsemen, have the advantage of being easily cleaned and provide a relatively unfavorable medium for the de- velopment of parasites. If wooden standings are used, the timber should be sound. Rotten, moisture-soaked floors are difficult to keep clean, and they provide a favorable medium for the development of parasites. If standings of earth are used, it is advisable to re- move the top layer of soil down to 10 or 12 inches once or twice a year and replace it with clean, uncontaminated soil. Horses should be fed grain from feed boxes and hay from racks which are sufficiently high above the ground or the floor of the stall to prevent contamination of the feed with manure. Watering troughs should be so constructed as to prevent similar contamination of the drinking water. Horses should not be forced to obtain drink- ing water from pasture or barnyard pools. In general, low, wet pastures are more favorable for the propagation of parasites than are high, well-drained areas. Animals grazed on heavily stocked, permanent pastures have greater opportunity for picking up para- site eggs and larve than those changed frequently from one pasture to another. For this reason pastures should be changed as often as @ PARASITES AND PARASITIC DISEASES OF HORSES 3 possible. The common practice of spreading horse manure on pas- ture plots adds to the parasite burden of the pastures. Suitable treatment of manure before spreading, as described in this circular, | will prevent this added contamination. MEDICINAL TREATMENT It is not always practicable on the average farm to apply the sanitary measures necessary for the prevention of parasitic infesta- tion in horses. Treatment is, therefore, an important consideration. Periodic treatment will not only reduce infestation in parasitized horses and render the animals more serviceable but will likewise reduce the output of eggs in the manure, with a resultant decrease in stable and pasture contamination. Prevention of parasites in horses by the application of sanitary measures is the business of the horse owner, but the diagnosis and treatment of parasitic diseases are functions of the veterinarian. Different parasites require different and more or less specific treat- ments. Before these treatments can be intelligently applied it is necessary to know which species of parasites are present. The veteri- narian is qualified by training and experience to ascertain this. Drugs used in treatments for horse parasites should be adminis- tered, as a rule, in capsules or by stomach tube, the latter being the preferred method for certain drugs. If capsules containing an irri- tant or volatile drug are broken in the mouth, some of the drug may be drawn into the windpipe and cause serious consequences. All drugs used in the treatment of horse parasites are poisonous, being intended to poison the parasites, and great care must be used in selecting the dose in accordance with the weight and condition of the animal. Some drugs should not be used in the presence of certain conditions and, if used under such unfavorable circumstances, may cause serious results. Because treatment involves diagnosis and an intimate knowledge of how a drug acts and when to use it or not to use it, it 1s advisable that all treatments for horse parasites be administered by a veterinarian. The treatments recommended in this circular are, for the most part, those which have been found by experimentation to be the most effective for the parasite or parasites involved. Many drugs, some of them long purported to .be of value for the expulsion of worms from the horse, have been found to be practically worthless for this purpose when critically tested. Among such preparations may be mentioned iron sulphate, arsenic, copper sulphate, and tartar emetic. These drugs are frequently prescribed for adminstration in the feed, a method which is very unsatisfactory and ineffective even with drugs known to be effective when given in capsule or by stom- ach tube. For this reason it is essential to administer worm reme- dies in accordance with the methods recommended in this circular. Before the administration of worm remedies animals should be fasted for the length of time prescribed under the various treat- ments. The withholding of feed reduces the bulk of the contents of the digestive tract and permits the drug to reach the parasites more certainly and effectively. Water should be allowed during the period of preliminary fasting, but it is advisable to withhold both feed and water for four or five hours after dosing. To keep 4 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE parasitic infestation at a minimum and avoid losses from this source, it is advisable to adopt a program of regular treatment. The usual procedure is to administer treatments twice a year. In the northern part of the United States, animals may be treated for worm parasites in the late spring or early summer and in the fall. In the South, owing to the shorter and milder winter and the more abundant warmth and moisture, it may be necessary to treat oftener. Judg- ment, based on experience, is a better basis for procedure than any general rule. Treatment for the removal of bots may be adminis- tered 30 days after the first freezing weather lasting 24 hours or longer. Tpternel parasites occur in various locations in the body of the host animal, such as the alimentary canal, lungs, liver, kidneys, blood, and various organs and tissues other than the skin. They include various forms of animal life known as Protozoa, worms, the larval forms of certain insects, and some forms closely related to insects. The various kinds are discussed in detail in the following pages: PROTOZOA Protozoa are relatively low forms of animal life, microscopic in size, and consisting of but a single cell. The parasitic Protozoa of domesticated animals are known to occur in various locations, and are especially common in the alimentary canal and in the blood. Fortunately, horses in the United States are relatively free from certain disease-producing protozoan parasites which occur in horses in other parts of the world where they constitute a limiting factor in horse production. The only known pathogenic protozoan para- site of horses in this country is the organism, one of the trypano- somes, which produces dourine.* Trypanosomes closely related to this organism occur in the blood of horses in South America, Asia, the Philippine Islands, and elsewhere and produce serious and fatal diseases. Up to the present time these parasites have not become established in this country, and quarantine measures to keep them out are enforced. Protozoan parasites of various kinds often occur in large num- bers in the cecum and the upper colon of horses, but these forms are not definitely known to produce any digestive or other disturb- ances and are usually regarded as comparatively harmless. WORM PARASITES The worm parasites of horses include flukes, tapeworms, and roundworms, the last-mentioned group being the most common and the most injurious. FLUKES Flukes or trematodes are soft, more or less flattened, leaf-shaped worms, occurring in various locations, especially in the digestive tract and in organs which communicate with the digestive tract. Only a few kinds of flukes are known to occur in horses, and several 3Information concerning dourine is published in Farmers’ Bulletin 1146, Dourine of Horses. ; PARASITES AND PARASITIC DISEASES OF HORSES 5 of the forms which have been reported from these animals normally occur in other hosts and are only accidental parasites of the horse. The only fluke likely to be encountered in horses in this country is the common liver fluke of cattle and sheep, which is occasionally found in the horse. Horses on the west coast, in the South, and in the Southwest are likely to become infested with liver flukes, espe- cially if they have access to pastures on which fluky sheep and cattle have grazed. Liver flukes occur in the bile ducts of the liver and produce a serious disease, especially in sheep. ‘The larval forms of these worms require snails as intermediate hosts and can maintain themselves only on pastures sufficiently wet to favor the occurrence of certain kinds of snails. Liver-fluke disease in horses has not been extensively studied, because it is relatively rare in these animals. Prevention consists in keeping horses off low and swampy pastures, and these precautions should be especially observed in those parts of the United States where liver flukes are known to occur. Such pastures favor parasites in general. Farmers’ Bulletin 1330 gives information on fluke control. Treatment.—There is no established treatment for liver-fluke in- festation in the horse. However, carbon tetrachloride in small doses has a specific action on the common liver fluke of sheep and is widely used as a treatment for fluke infestation in these animals. Carbon tetrachloride may be given with safety to adult horses in doses of from 6 to 12 fluid drams (25 to 50 cubic centimeters) and in these doses should be effective for the destruction of the flukes. TAPEWORMS A tapeworm is an elongated flattened worm consisting of a head and a chain of segments. Each mature segment contains both male and female organs. The head of a horse tapeworm is provided with four suckers by means of which the parasite attaches itself to the wall of the gut. The segments of these tapeworms are considerably wider than long and those which are farthest from the head are the ones which contain eggs. The ripe or gravid segments which con- tain the eggs become detached from the rest of the chain and are expelled from the body with the droppings. Beyond this point nothing is known as regards the further development of horse tapeworms. Horses are known to harbor three species of tapeworms, as follows: The large horse tapeworm, Anoplocephala magna (fig. 1), usually is from 31% to 10 inches long. The head is about two-fifths of an inch in width and bears four prominent suckers. With the excep- tion of those immediately adjoining the head, the segments are con- siderably wider than the head. This parasite occurs in the small intestine and occasionally also in the stomach. The dwarf tapeworm of horses, Anoplocephala mamillana (fig. 2), is only from about one-fourth of an inch to 2 inches long and from one-sixth to one-fourth of an inch wide; the head of this worm is very minute and is barely visible to the naked eye. This tapeworm occurs in the small intestine and is occasionally found in the stomach. A third species of tapeworm, intermediate in size between the large tapeworm and the dwarf tapeworm, is known as the perfoliate tapeworm, Anoplocephala perfoliata. It is usually from about 6 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE three-fifths of an inch to over 3 inches long. It occurs usually in the cecum and is also found in the lower portion, rarely in the upper portion, of the small intestine. This species is apparently much less common in American horses than the other two species of tapeworms. Symptoms and lesions——In light infestations no symptoms are present. Horses which are heavily infested with tapeworms may FIGURE 1.—AlImost a gallon of large tapeworms, Anoplocephala magna, removed post- mortem from a horse. About one-half natural size. (Photograph by courtesy of the Agricultural and Mechanical College of Texas) suffer from intestinal catarrh, show digestive disturbances of vari- ous sorts, and in cases of very severe infestations they may become emaciated and anemic. The perfoliate tapeworm of the horse often occurs in large numbers when present at all, and is said to produce inflammation of the intestines; sometimes it ruptures the wall of the cecum. The attachment of tapeworms of this species to the wall of the cecum produces small ulcers in the regions to which the worms are attached. Treatment.—Very little is known regarding treatment for tapeworms in the horse. The fol- Ficurp £—The dwarf lowing treatments have been recommended but EO nitine <= ~have not had critical test to determine their pre- phala mamillana, of : the horse. Natural cjse value. i Oil of turpentine is said to be an effective remedy. This is given in a dose of 2 fluid ounces (60 cubic centi- meters) in capsules, followed every second day by 1 ounce (30 cubic centimeters) in capsule until five or six doses have been given. The last dose is immediately preceded or followed by 1 quart of raw linseed oil. It would seem that the drugs used for the treatment of tapeworm infestation in other animals would offer more promise. a PARASITES AND PARASITIC DISEASES OF HORSES i. Areca nut may be of value for the removal of tapeworms from the horse. Areca nut, freshly ground, may be given to adult horses in doses of from 1 to 1.5 ounces (30 to 45 grams) in capsules after fasting the animals for 24 to 36 hours. The drug has a purgative action, but if the bowels do not move within four or five hours, it is advisable to administer 1 to 2 pints of raw linseed oil. Areca nut should not be given to very old or very young animals or to those in a weakened condition. Kamala may be found to be of value for the removal of horse tapeworms. Kamala may be given to adult horses in doses of 1 ounce (30 grams) in capsule, after they are fasted from 24 to 36 hours. The drug itself has a purgative action and seldom needs to be followed by a purgative. Kamala should not be given to very young or very old animals, to those in a weakened condition, or to those suffering from febrile diseases, such as influenza, distemper’ (strangles), and infectious anemia (Swamp fever). Oleoresin of male fern is another drug which may be of value for the expulsion of tapeworms from the horse. This drug may be iven to adult horses in doses of 3 to 6 drams (10 to 20 grams) in capsules after fasting the animal for 24 hours. The drug should be immediately preceded or followed by 1 quart of raw lnseed oil. The foregoing drugs should be used with caution and given only to animals in good condition and presumably able to withstand any poisonous effects of the drugs. Prevention—In the absence of information concerning the life histories of horse tapeworms no definite control measures can be recommended. It should be remembered in this connection that the eggs present in gravid segments which are eliminated with the manure are the starting points of new infestations. Any measures which are taken with reference to the proper disposal of manure will aid in preventing infestation with these parasites, especially if the manure is stored and permitted to undergo self sterilization by heating, so far as the destruction of parasite eggs and larve is con- cerned. ‘This procedure is described later in this circular. ROUNDWORMS Roundworms or threadworms comprise the vast majority of para- sites which infest horses. These worms, which are also known as nematodes, are elongated, cylindrical in shape, and usually tapering at both ends. Some roundworms are almost white, some are grayish white, most of them are yellowish in color, and some are pinkish or blood red. Roundworms occurring in the horse have a considerable range of size, the large, intestinal roundworm or ascarid being from 6 inches to over a foot long, while the small stomach worm is only about one-fifth of an inch long. Roundworms reproduce by means of eggs which are produced by the female worms. The eggs are usually eliminated from the horse’s body with the manure. Some species of roundworms must be taken up by an intermediate host in which they undergo part of their development, while other species are transmitted from one animal to another directly by eggs or by larvee which have emerged from eggs. Most roundworms which oc- cur in the horse are transmitted directly by eggs and larve, with- out the use of an intermediate host. 8 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE ROUNDWORMS IN THE STOMACH Two kinds of worms are present in the stomach of horses. One kind, designated here as the large stomach worms, is represented by three distinct species in the horse; these parasites are transmitted by flies. The other kind, designated as the small stomach worm of the horse, is represented by only one species. The small stomach worm is acquired by horses directly as the result of swallowing infective larvee which occur on pastures. The larve may also be taken in by horses with water and with dry feed. THE LARGE STOMACH WORMS The large stomach worms (fig. 3) are relatively long and slen- der, are whitish in color, and occur either free in the stomach, em- bedded in mucus, attached to the wall of the stomach, or in tumors 7 of the stomach wall, for which tumors these worms are respon- sible. One species, Carter’s stomach worm, Habronema muscae, of the - * inch to nearly an inch long. This parasite occurs free in the horse, is from about one-third stomach or attached to the wall of the stomach. A second spe- cies, the small-mouthed stomach worm, //. majus, synonym /. microstoma, 1s similar in size and appearance to the above species. While this form may A occur free in the stomach, it is capable of penetrating its wall FIGURE 8.—Large stomach worms of the and causing sores. A third spe- Perse. cai er onema_microsioma;y others Gees athe) lar ce-mouumeG scuonna tim worm, H. megastoma, of the horse is the smallest of the three species, ranging in length from less than one-third of an inch to about one-half inch. These worms occur in tumors found in the wall of the stomach; the tumors may become very large, attaining the size of a fist or even of a child’s head. Usually, however, they are much smaller. Life history.—(Fig. 4.) The eggs of horse stomach worms have very flexible shells; they are deposited in the lumen of the stomach and are eliminated from the horse’s body with the feces. When the eggs are swallowed by maggots of house flies, stable flies, or other flies which breed in horse manure, further development takes place which keeps pace with the development of the maggots. The larve of Carter’s stomach worm of the horse develop for the most part in house flies while those of the small-mouthed stomach worms of the horse have stable flies as their usual intermediate hosts, though they are known to develop also in house flies and other flies. The larvee of the large-mouthed stomach worms of the horse develop in various species of nonbiting flies, including house flies. These larvee attain their full growth in the flies when the latter emerge from the PARASITES AND PARASITIC DISEASES OF HORSES 9 pup. Horses may become infested with stomach worms as a result of swallowing live, infected flies or infected flies which have been dead a short time and still contain the live larval worms. Another and probably more common way in which horses become infected with these parasites is as follows: As the flies suck the moisture of the lips and nose, the larvee, which are present in the mouth parts of the insects, escape, the heat and moisture of the horse’s body stimulating the larve to wriggle out of the flies. Once TE €995 COMIMaMIIG YOUNG, worms are expel/ed Yrom the digestive / (a) track wit SIQHUPE. The 17a@+tlre Worms 17 The Storiath lap 17101 EGGS. lhe eggs are swallowed by fly WHNAG907S (a) he young worms avelop Wt the rnaggor and tr the pupa tb) and are infective wher the adiu/7 Sly (€) ernerges. Horses become tifested as / aresul? of swallowia ph ae “pected files or Be Cy i) Sorvae which escape ~te Jrom flies while the latter are feeding on the mosture of the lips: 4 Ficurn 4.—Life cycle of one of the large stomach worms, Habronema muscae, of the ‘horse. The illustrations of the adult worms are enlarged about 2 times; those of the eggs are enlarged about 150 times. the larve are on the lips they are readily swallowed. Those larve which get into the nasal’ cavities probably wriggle into the pharynx and are also swallowed. When the larve reach the stomach they are in their normal location where they settle down and develop to maturity. It is possible that the small-mouthed stomach worm is transmitted by the bite of the stable fly. Symptoms and lesions —No definite symptoms which indicate the presence of these parasites in the stomach are known. The worms are injurious because of their tendency to attach themselves to and to penetrate into the stomach wall and, in the case of the large-mouthed 13423 (———e 10 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE stomach worm, because of the tumors which they produce. The tumors interfere to a considerable extent with the proper functioning of the stomach. When large tumors are situated near the junction of the stomach and intestine they interfere mechanically with the passage of food. The most evident injury occasioned by the large stomach worms is produced by the larve which get into the skin of horses where they are commonly associated with a skin disease known as Summer sores. Treatment.—A high degree of efficacy for the destruction of Z. muscae and H. microstoma has been obtained by the use of the fol- lowing method of treatment. The animal should be fasted for from 18 to 24 hours and the stomach washed out by injecting through a stomach tube 8 to 10 quarts of a 2 per cent solution of sodium bicar- bonate (baking soda) heated to 105° F. The solution tends to remove the thick layer of tenacious mucus which normally covers the lining of the stomach and renders the stomach worms more accessible to the action of drugs. It is advisable, though not necessary, to siphon off the sodium bicarbonate solution. If the solution is not siphoned off, an interval of 15 to 20 minutes should elapse before further treatment. Carbon disulphide should then be administered in capsule or by stomach tube in a dose of 6 fluid drams (24 cubic centimeters) for a 1,000-pound animal, or at a dose rate of 1.5 fluid drams (6 cubic centimeters) for each 250 pounds of weight. No purgative should be used with this treatment. H. megastoma in stomach tumors is not affected by this treatment and is inaccessible to any method of treatment known at present. Prevention.—Prevention of stomach-worm infestation in horses involves the storage of manure in closed containers, in order to de- crease the number of flies which breed in manure, or the application of other control measures designed to prevent flies from breeding. The use of containers for storing manure with a view to destroying egos and larve of parasites is discussed subsequently in this circular. The United States Bureau of Entomology has devised a trap de- signed to destroy fly maggots which breed in manure. ‘The trap is based on the observation that maggots, when fully grown, migrate out of moist manure and if they are permitted to escape through spaces between the boards of an open manure platform raised on posts and set in a concrete basin of water, they are caught in the basin and drowned. This and various other methods of controlling the house fly and stable fly are given in Farmers’ Bulletins Nos. 1408 and 1097. SUMMER SORES A skin disease of horses, known as summer sores and characterized by pronounced skin lesions, is associated in some parts of the world, including the United States, with the larve of the large stomach worms of horses. The sores may be as small as a millet seed, but are usually about the size of a pea and may attain a size about an inch in diameter. The sores are covered by a soft, brownish-red, pulpy material with cracks or furrows which are filled with pus. In the midst of the softened mass there are small, rounded granu- lations which are firm in texture, PARASITES AND PARASITIC DISEASES OF HORSES 11 This disease has been studied in Europe, Africa, and elsewhere, where it has been noted that its seasonal occurrence corresponds to the prevalence of flies. It is unlikely that the worm larve invade the unbroken skin, but it appears to be well established that when a horse’s skin is broken by some injury and when flies which carry the worm larve feed on the sores, the larvae escape from the mouth parts of the fly and live for a time in the wounds. These larvee irri- tate the sore, so that instead of healing as a simple sore it may become a more or less chronic thing which does not heal until after the occurrence of frost in the fall. Although conditions known as “summer sores” in horses are known to occur in the United States, the disease has not been exten- sively studied here and the relation of stomach-worm larve to sum- mer sores still needs further investigation in this country. Recently the occurrence of the larval worms from summer sores in horses in the United States has been definitely reported. Treatment for summer sores.—An astringent powder which is said to prevent the extension of the trouble and to aid in healing consists of the following: Plaster of Paris, 100 parts; alum, 20 parts; naph- thalene, 10 parts; and quinine, 10 parts. Good results are reported from the use of a caustic paste composed of arsenious oxide, 1 part, and flour, 5 parts. Washing the sores with ether or chloroform and then painting them with collodion has also been recommended. Some veterinarians prefer the use of a 5 to 10 per cent solution of formalin, applied by means of a cotton pad which is left on the sores for two to three hours every day. Prevention.—Skin injuries should be protected from flies by the use of pine-tar oil or other means to prevent their conversion into summer sores. THE SMALL STOMACH WORM This parasite, 77ichostrongylus awxei, occurs in the lining of the stomach, and is likely to be overlooked as the worms are very slender and only about one-fifth of an inch or less in length. Life history.—The life history of this parasite has not been defi- nitely ascertained. In a general way its life history is similar to that of blood strongyles, described elsewhere in this circular, with respect to the development of the eggs and larve on pastures. It is also fairly certain that infestation is direct, and results from the swallowing, by horses, of the infective larve with food or water. However, these worms burrow only into the stomach wall and are not known to wander extensively, as young worms, throughout. the body of the horse. Symptoms and lesions——These parasites injure the stomach wall. Sometimes the stomach lining shows areas superficially like a ring- worm or a mass of small tumors. (Fig. 5.) In addition to these injuries, the parasites contribute to general gross parasitism in horses which is characterized by weakness, paleness of the mucous surfaces, wasting, and digestive disturbances. Treatment.—Treatment for the removal of this parasite is similar to that recommended for the large stomach worms. However, this treatment has not had critical test to determine its exact. efficacy against the small stomach worm. 1,2. CIRCULAR 148, U. 8. DEPARTMENT OF AGRICULTURE Prevention.—Preventive measures are similar in a general way to those discussed in connection with preventive measures against blood- worms and other strongyles. The similarity in control measures is based on similar life histories. THE LARGE INTESTINAL ROUNDWORMS OR ASCARIDS The large intestinal roundworms, Ascaris equorum, of horses (Fig. 6), also known as ascarids, are cylindrical in shape, yellowish white in appearance, and from about the size of an ordinary lead pencil to about a foot long when fully grown. The head is clearly marked off from the rest of the body and bears three clearly distinguishable lips. Closely related worms occur in pigs, cattle, and human beings. Ascarids occasionally pass out of the bowels spontaneously, in which FicurE 5.—Portion of the inner lining of a horse’s_ stomach, showing lesions produced by the small stomach worm, Trichostrongylus azei. (Photograph by courtesy of the Agricultural and Mechanical College of Texas) case they are readily seen, and in horses this is said to take place in the spring of the year. These worms are located in the upper part, less often in the middle and lower parts, of the small intestine; they are occasionally found in the cecum and in the stomach. They may occur in large num- bers, especially in foals and in young horses. Life history—(Fig. 7.) The female worms produce large num- bers of eggs which are microscopic in size. The eggs are deposited in the lumen of the horse’s intestines and are expelled from the bowels in the manure. Under favorable conditions of temperature and with an adequate supply of moisture, the eggs develop on the ground and on pastures until they reach the infective stage, but the embryos remain in their eggshells until they reach the gut of a sus- ceptible horse. The thick eggshell protects the embryo it contains against various unfavorable influences. i PARASITES AND PARASITIC DISEASES OF HORSES 13 During the summer months the eggs develop to the infective stage in about two weeks. The low temperatures of cold weather retard the development of the eggs, as does also lack of moisture. Ordinarily sufficient moisture is present in horse ma- nure to favor the development of the eggs. Balls of manure which appear dry on the surface commonly contain sufficient mois- ture in the middle to permit the normal development of these eggs. Excessive drying destroys the vitality of ascarid eggs, If infective ascarid eggs are swallowed by horses with grass, water, or dry feed which has become contaminated with horse manure, the embryos are liberated from their shells in the horse’s intestine and then burrow into the wall of the gut and migrate with the blood stream to the liver. From this organ they proceed in the blood stream through the heart to the lungs. If many worms go through the lungs at the same time they injure this organ and may produce pneumonia. This roundabout journey from the intestine to the liver and thence to the lungs is completed in about a week. From the lungs the larve crawl up the windpipe until they reach the back of the mouth and are then swal- lowed. On getting into the small intestine from the stomach for the second time, they settle down and develop to maturity in from about two to two and a half months. (Fig. 8.) Symptoms and lesions—When ascarids are present in large numbers, which is likely to be the case in foals and young horses, they produce digestive disturb- ances of various sorts and may cause colic. These parasites frequently become entan- gled with one another, resulting in large masses of worms which may plug the lumen of the intestine. In an extreme con- dition of this sort the results may be fatal. Such an entangled mass of worms may even rupture the wall of the intestine as a result of continuous pressure on it. These worms have also been reported as being capable of perforating the wall of the intestine, presumably as a result of continually pushing their heads against it. Ficure 6.—The large roundworm, Ascaris equorum: A, male; B, female. About one-half natural size In either case, a rupture of the intestinal wall would usually cause the death of the horse. In experimental infestations of horses with ascarids, fever and a cough have been observed during the early stages when the 14 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE worms were present in the lungs and in the windpipe and its branches. It is probable that similar symptoms are present in heavy ascarid infestations which are acquired naturally in stables and on pastures. Ordinarily, ascarid infestations in foals result in un- thrifty animals with rough, staring coats, and the removal of the worms frequently leads to marked improvement in condition, hair coat, and gain in weight. Thus it is evident that the ascarid, both as an adult and as a wandering larva, has the capacity for causing great damage, and that its presence in horses, especially foals, is a possible source of 2 aepelOpird da CS )') ZZ The eggs are expelled with the tnarure and develop =3 One Ground and © = 4 O17? PAUSTUES: S Chaer favoratle CONANHONS ThE EUGS EAC? the Ufective stage li abour 1WO WEEKS. >” The rya@7vure HOTS i the itestiies lay PROUSQIIOS SS COGS: Horses becore iifested as a restl? of swallusing Wifective eggs wills Jood or ware Ficurn 7.—Life cycle of the horse ascarid, Ascaris equorum. The eggs shown in this illustration are enlarged about 50 times danger. Heavy infestations, in which hundreds of worms may be present, may cause illness and even death as a result of the horse’s absorption of toxic products produced by the worms. Treatment.—Carbon disulphide is an effective remedy for the re- moval of ascarids from the horse. The drug is given as follows: Fast the animal for 18 hours and give carbon disulphide in a dose of 6 fluid drams (24 cubic centimeters) for a 1,000-pound animal or at a dose rate of 1.5 fluid drams (6 cubic centimeters) for each 250 pounds of weight. The worms usually pass for several days follow- ing treatment. Purgatives should not be given with this treat- ‘15 arbon ) I C f inflammation in the PARASITES AND PARASITIC DISEASES OF HORSES of the carbon disulphide. Fats and oils should be avoided as they promote the absorp- disulphide usually produces a limited area o tion and increase the toxicity ment. estoy B Jo Apog oy} Ysnoriy} AouAnOl sprlavose ayg—'s TAs ( ron 33s ) ‘GNNOWD ( VON 35S ) ‘STSaSS3A AHL NO S993 SHL AGISNI WHOS goold NI LHVSH AHL OL O09 SWYOM ONNOA SYSSM M34 V NI SWYHOM ONNOA YSAII WOud . t ml ( SON 33s ) "ANNOYS SHL OL W1V4 GNV SYNNVAW NI AGOg 40 1NO SSvd ‘SSNILSSLNI NI SAYOM AYNLVW AG GaondO"Ud S993 \y NI | | | | | | (GON 33S) YS9YV1 SSWIL TWHSAES MOXOS GNV S1T4SSS3A Goold NI SONNT OL O09 SWHYOM ONNOA ‘LYVSH WoOYSs (€'ON 33S) SlasssA dooig NI Y¥3AIN OL OOD SWHOM ONNOA GNV SSNUSSLNI NI HOLVH S993 ( 9'ON 33s ) GSMOMVWMS 3YvV ONY HLNOW 3O MOVE OLNI AdIdGNIM dN IMVeO SWYHOM,ONNOA *SONNT NI SAVO Mas V YSIdV <_L > ge Li ‘ZIVG 3 \ aS 4, | (€ 20ON 33s) aamonvwms \ 141 aZ/ | GNV GNNOYo Wows dN | Gadd Adv SWHOM ONNOA | | | ONINIVLNOD S993 WHOM | ( Z°ON 33S) ‘s9903 430 SNOIMMIW FONdOdd GNV SANILSSLNI NI SAM OL SNNILNOO ASHL "SHLNOW Z LNOGV NI ALINMLVIN OL MOXOS ‘GaMOTIVMS SYHV ~ GNV SON HONOYHL GSSSVd SAVH LVHL SWHOM ONNOA ‘. 3 a © =a (A The animal should Experimental investigations indicate that carbon tetrachloride is also very effective for the removal of ascarids. be fasted 18 hours and the carbon tetrachloride given in doses of stomach of the horse. This inflammation is without serious consequen- ces, however, and usually disappears in the course of a week or two. 16. CIRCULAR 148, U. 8. DEPARTMENT OF AGRICULTURE from 6 to 12 fluid drams (25 to 50 cc) for a 1,000-pound animal. This drug usually need not be accompanied with a purgative, but it is advisable to give a saline purgative immediately following the administration of carbon tetrachloride for the removal of worms, particularly ascarids, from colts. Prevention.—Prevention of ascarid infestation requires special care of foals and young horses. The time to begin is before the foal is born. The foaling barn should be of sanitary construction and should be cleaned and washed with hot water and lye before the pregnant mare is placed in it. The mare and foal should be kept in a clean paddock adjoining the barn. It is best to use a paddock from which other horses have been absent for at least a year. The stable and paddock in which the mare and foal are kept should be cleaned daily if possible, lit- ter and manure be- ing removed. These precautions are designed to pre- vent the foals from becoming heavily infested with asca- rids at an early age, and beforethey have developed the neces- sary reserve vitality to cope successfully with a heavy worm infestation. When the foal is moved to a. pasture it 1s essen- tial to select one which is clean and that has not been used by horses for a year or oncer Horses may be FIGURE ripe al es Leek Sea Note accumu- moved to cow and sheep pastures and vice versa, because parasites of ruminants are not transmissible to horses, and equine parasites are not transmissible to cattle and sheep, as a rule. Proper disposal of manure and sanitary meas- ures recommended in connection with the control of blood strongyles will also help to prevent infestation with ascarids. While infestations with ascarids can be acquired on pastures, and often are so acquired, it is important to remember that ill-kept stables, in which manure is allowed to accumulate (fig. 9), are also the sources of heavy infestations with intestinal roundworms, pin- worms, and other threadworms. Under pasture conditions many eggs and larve succumb to drought and to other unfavorable in- fluences which prevail in the open. In manure-laden stalls parasite ¢ PARASITES AND PARASITIC DISEASES OF HORSES LW. eggs and larve are largely protected from unfavorable influences and they have an abundant supply of moisture and shade and a favorable temperature for development. It is, therefore, important to pay strict attention to stable sanitation and to remove manure frequently, supply fresh bedding, clean water from sanitary watering troughs (fig. 10), and dry feed in feed boxes and racks well raised above the floor in order to prevent contamination with horse manure and con- sequent gross infestation with these parasites. (Fig. 11.) STRONGYLOIDES Foals are commonly infested with very small and slender thread- worms, Strongyloides westert, which occur in the small intestine. These parasites, all of which are females, are whitish in color, about FIGURE 10.—Type of sanitary watering trough one-third of an inch long, and less than one two-hundred-and- fiftieths of an inch wide. These threadworms produce numerous eggs, microscopic in size. and deposit them in the intestine of the infested foal from which they are eliminated in the manure. The eggs develop very rapidly on the ground and on pastures, and the larvee which emerge from them may either transform directly into infective larve which serve to infest other foals, or may develop into free-living males and fe- males. As a rule both types of development take place, some larve becoming infective while others develop into free-living adults. The latter mate on the ground or in manure and the females produce eggs and deposit them on soil or in manure. In a short time, under favorable conditions, larvee emerge from these eggs. These larve become infective and are capable of infecting horses. UPS By 8 18 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE These parasites multiply very rapidly, the entire development on the ground taking place in a few days. The infective larvee, whether they hatched from the eggs eliminated with the feces or from the eggs produced by the free-living generation of worms, are taken in by horses with food and are also capable of penetrating the intact skin. Within about two weeks after the larve have been taken up by horses they have developed into mature females which soon begin to discharge eggs into the intestine of the host. Symptoms and lesions—While no definite symptoms have been described in horses as resulting from infestation with these parasites, ) the worms are prob- ably responsible for diarrhea in foals, These worms make their appearance in foals earlier than do other parasites, and the infestation tends to become heavy as a result. of reinfesta- tions which may take place rapidly and often, because of the brief period required for development out- side of the host. The parasites are usually embedded in the lin- ing of the intestine and doubtless produce considerable irrita- tion. The fact that the infective Jarve are capable of pene- trating the skin adds another complication and it is probable that foals acquire part of their infestation while lying down on _ pas- Rs ie i, cate RUC Hi inaan Sent tures and in_ their IGURE -—1type or Sanitary box stall. INOUE) Lee ox and hayrack raised above the ground stalls. As the larve penetrate the skin it becomes reddened and obscure skin troubles in horses may be caused by the penetration of these worms. The larval worms may carry pathogenic bacteria into and through the skin. Treatment.—N othing is known concerning effective treatment for these threadworms. In severe cases of diarrhea, in foals, caused by this parasite, carbon tetrachloride is worthy of trial. The drug may be used for foals at a dose rate of 0.1 cubic centimeter per kilogram (2.2 pounds) of body weight or 10 cubic centimeters (2.5 fluid drams) for a 220-pound animal. In order to remove the bulk of ingesta in the small intestine and render the parasites more accessible to treat- ment, it is advisable to administer a purgative 24 hours before treat- 9 PARASITES AND PARASITIC DISEASES OF HORSES 19 ment, and to withhold feed until after the carbon tetrachloride has been given. A suitable purgative for foals consists of castor oil, 4 to § ounces, and neutral oil (mineral oil) 1 pint. This treatment has not had critical test to determine its precise value. Prevention.—Prevention consists in special precautions with ref- erence to stable sanitation, special care of foals, especially as regards clean bedding which should be changed daily, if possible. Other preventive measures are similar to those recommended in connection with the discussion of ascarids and blood strongyles. THE LARGE STRONGYLES OR PALISADE WORMS The large strongyles are roundworms commonly known as blood worms, red worms, sclerostomes, or palisade worms. ‘They are red in Figure 12.—Portion of the tip of the cecum of a horse, showing blood strongyles attached to the inner lining of the gut. The large worms are 8. equinus; the smail ones are S. vulgaris. Natural size color and are commonly found firmly attached to the wall of the gut (fig. 12) by means of a rather formidable mouth cup. Three species of blood strongyles are of common occurrence in the colon and cecum of horses, as follows: The large strongyle, Strongylus equinus (fig. 138, C), is from about 11, ‘to nearly 2 inches long by about one twenty-fifth to one- twelfth of an inch wide; the mouth cup contains three teeth. The toothless strongyle, Strongylus edentatus (fig. 18, A), contains no teeth in its mouth cup; otherwise it is similar in appearance to the large strongyle, although it is somewhat smaller, females being about 114 inches long. The single-toothed strongyle, Strongylus vulgaris (fig. 18, B), is the smallest of the three species, and is from a little 20 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE over half an inch to about an inch long and less than one twenty-fifth of an inch wide; this worm contains a single tooth in its mouth cup. This tooth has two prominent, rounded ‘projections and on casual examination two teeth appear to be present. Life history —The eggs of blood strongyles are discharged into the intestine of the host and are eliminated from the body with the feces. (Fig. 14.) Under favorable conditions of temperature and moisture the eggs develop rapidly on the ground and on pastures and hatch in a day or so. The larva which emerges from each egg which develops normally, feeds on the contents of the manure in “which it finds itself and after it undergoes two molts in more or less rapid succession it becomes infective. This entire development on the ground or on pasture takes place in a week or so during the warm months and i is delayed considerably during the cold months. Lack of moisture is unfavorable to the developing eggs and larve, but ordinarily there is sufficient moisture in horse feces to favor normal development, provided the temperature is favorable. Shade affords FIGURE 13.—Head ends of the three species of blood strongyles: A. S. edentatus; B, S. vulgaris; C, 8. equinus. Enlarged. From Looss, 1901 protection to the eggs and larve and it is likely that direct sunlight is more or less injurious to them. The infective larve are very resistant to unfavorable conditions and are probably capable of maintaining themselves on pastures for long periods. ‘They remain ordinarily in or near the manure where they hatch; however, they are doubtless scattered by rain and wind and may reach places on pastures relatively remote from their original locations. When the air is sufficiently moist so that the grass becomes covered with a film of moisture, as happens in times of rain, dew, or fog, the larve migrate up the grass blades and this brings them to a favorable situation to be swallowed by horses while grazing. So far as is known, these larve do not penetrate the skin and must infect horses by being swallowed with grass, water, or dry food which has become contaminated with the larve. The course of development of these parasites after they get into the body of horses has not been definitely ascertained; it is “known. however, that not all larve, and perhaps none of them, go down directly into the cecum and colon and settle there and grow to PARASITES AND PARASITIC DISEASES OF HORSES PAM maturity. On the contrary, the larve, after entering the body of the horse, undergo extensive migrations which bring them to various organs and tissues, such as the liver, pancreas, spleen, lungs, kidneys, and other organs and tissues, from which many of the larve prob- ably fail to get back to the large gut. However, those larvee which return to this organ become attached to its wall and develop to fertile maturity. The eggs which are produced by the female worms and eliminated from the horse’s gut with the manure start the cycle of development once more. Logs reach the pasture With the 1arrire O70 evelgp tr abou? a day Or two Uwraer- SJavorable £995 (aTch) O77 conditions, [faerie tit le | larvae (a) develop ro the uyfectwe stage (b/) tt O07 @ wee OF FO under favoratle conitiins, Native WOrMS la digestive tract of the horse lay 17arly €GGE. a YY | hipective larvae Sr chink up blades Sf. YASS 177 wer weather 6 Horses Lecone liifested as @ result of swalloning Wective larvae ith ass: Ficurn 14.—Representation of the life history of one of the blood strongyles, S. equinus. The illustrations of the adult worms are about natural size and those of the eggs and larve are enlarged about 75 times. ‘This iilustration is typical of the life cycle of horse strongyles generally From this account of the life cycle of these parasites it is evident that horses infested with blood strongyles contaminate the pastures on which they feed with the eggs produced by the worms, and that the larvee which issue from the eggs and develop to the infective stage may be swallowed by these and other horses. When horses are kept on the same pastures year after year the number of eggs and larvee gradually increases, and this contamination, accumulating from year to year on a given pasture, may be highly damaging to horses which are grazed there. Foals, in particular, suffer from the effects of gross parasitism acquired in this manner. 22 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE Symptoms and lesions.——The blood strongyles injure the wall of the gut to which they are attached. These worms suck a tuft of the inner wall of the gut into their mouth cups (fig. 15) and abstract blood from this delicate lining. As the worms move from one place to another within the gut they expose its injured wall to the entrance of disease-producing bacteria. Bloodworms abstract blood from the finer blood vessels in the lining of the gut, and when many worms are present in a horse at the same time the loss of blood may be considerable and may lead to anemia with the usual consequences of weakness and of watery swellings (edema) in various parts of the body. These worms also produce injuries of various sorts in the parts of the body to which they wander, such as the liver, pancreas, and other organs. One species, the single-toothed strongyle, is espe- cially injurious be- cause as an imma- ture form it settles in certain arteries, especially in the an- terior mesenteric artery which" sup- plies blood to the large gut. As a re- sult of the presence of the worms in this blood vessel, the wall of the artery, where the worms accumulate, becomes thickened and Beer ta arena coectsee ace Seeing eme'de S. equinus, with a tuft of the inner lining of gut dreiwa ably to form what fe He see ge of the worm. Greatly enlarged. is known as an aneurism. An aneurism is a spindle-shaped, cylindrical, or globular dilation of a blood vessel and often contains a heavy deposit of fibrin inside. In the horse it may attain the size of a child’s head. (Fig. 16.) An aneurism interferes to a considerable extent with the circula- tion of blood through the affected artery, because the heavy deposits of fibrin inside may almost obliterate the lumen of the blood vessel. This condition results in a diminished blood supply to the large intestine; when the intestine becomes anemic as a result of this it becomes predisposed to colic, twist, and intussusception, the last being a condition in which part of the gut slips into an adjoining part. When a piece of fibrin deposit in the aneurism breaks loose, it may be carried in the circulation to a terminal portion of an artery and may lodge there as a plug. As a consequence, the circulation to a part of the large gut may be completely shut off. Such a con- dition interferes with the functions of the large gut, produces an anemic condition with the consequences noted above, and in extreme PARASITES AND PARASITIC DISEASES OF HORSES 93 cases may produce death. It is believed that most cases of colic in horses result from such disturbances in the blood circulation of the gut. Ifthe plug forms in a hind leg it may cause a form of intermit- tent lameness. Aside from the injuries described, mixed parasitic infestation, known as strongylidosis, results when blood strongyles occur in large numbers and in association with other species of roundworms in the large gut, particularly when horses are kept on permanent pastures. This condition is widespread in horses and is usually more injuri- ous to foals and young horses than to older horses. Strongylidosis is frequently mistaken for infectious anemia or swamp fever and cases diagnosed as swamp fever, in many instances, have cleared up fol- lowing the removal of worms by medicinal treatment. ‘The common symptoms of strongylidosis are diarrhea, weakness, and emaciation. The digestive disturbances result from the irritation to the ning FIGURE 16.—A small aneurism of the anterior mesenteric artery of the horse, partly cut open to show worms and the heavy deposit of fibrin inside. The worms are immature forms of Strongylus vulgaris, Natural size of the gut produced by the parasites. At first the diarrhea is slight and the soft manure has a bad odor and contains poorly digested food material; later the diarrhea becomes more pronounced, with softer feces. The appetite, which is irregular at first, becomes poorer and finally the horses are off feed. As a result of their weakened condition, affected horses find difficulty in chewing, may throw out mouthfuls of feed, and then reject feed altogether. This leads to further emaciation which becomes very marked. As the disease pro- gresses the bones become prominent, the coat becomes rough, the eyes are sunken, and the animal becomes greatly weakened. (Fig. 17.) With these symptoms there are marked changes in various tissues and organs of the body. The working capacity of horses which are suffering from strongy- lidosis is decreased considerably even before the symptoms become very pronounced, and in the absence of treatment such horses are able to do less and less work as the disease progresses. It has been found that when horses are treated for the removal of parasites many of the symptoms described above disappear, the animals take 24 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE on weight, regain their working capacity, and make an all-round improvement. Treatment.—It is advisable to fast the animal 36 hours before treating for large strongyles. Oil of chenopodium is effective for their removal. This drug should be given in a dose of from 4 to 5 fluid drams (16 to 20 cubic centimeters) for a 1,000-pound animal, or at a dose rate of 1 fluid dram (4 cubic centimeters) for each 250 pounds of weight, immediately preceded or followed by 1 quart of raw linseed oil or by an aloes ball. Cases of excessive purgation have been reported in some instances following the use of raw linseed oil. It is possible that this undesirable action is due to impurities in the product; conse- quently a good grade of oil should be used. A mixture, said to be without the undesir- able effects of raw linseed oil, has been recommended as fol- lows: For wean- lings, castor oil, 4 to 6 ounces, and neu- tral oul, 1 pint; for yearlings and 2-year- olds, castor oil, 6 to 8 ounces, and neutral onl: dsspimt >; torso" year-olds and older, castor oil, 8 to 10 ounces, and neutral oil, 114 pints. Figure 17.—Horse suffering from gross infestation with : Carbon tetrachlo- parasites (strongylidosis). Note marked emaciation. ride is also of value Fe eee Ge lame removal of parasites, this for ther removal of large strongyles. It should be used in treating pregnant mares as oil of chenopodium is dangerous for such animals. It may be given in doses of 6 to 12 fluid drams (25 to 50 cubic centimeters) for a 1,000-pound animal. Normal butylidene chloride is another drug which is effective for the removal of large strongyles. It should be given in a dose of 3 fluid ounces (90 cubic centimeters) for a 1,000- pound animal, and followed in five hours by raw linseed oil at the rate of 1 quart per 1,000 pounds of weight. It is gales Oy that the dose of normal butylidene chloride could be reduced to 2.5 ounces (75 cubic centi- meters) for a 1,000-pound animal, without materially reducing the efficacy of the drug. One treatment with any drug will not always remove all worms present and, if necessary, tre atment may be re- peated in from four to six weeks. As a supplement to worm treatment, distinct benefit has been obtained from the use of tonic drugs such as sodium cacodylate or ferrous sulphate. Such drugs aid in the formation of red cells and hemoglobin and assist the animal to overcome the anemia associated with strongyle infestations. Sodium cacodylate is recommended for use in subcutaneous injections in a dose of 45 grains in 10 cubic PARASITES AND PARASITIC DISEASES OF HORSES 25 centimeters of distilled water once a week. Ferrous sulphate may be given in a dose of 2 drams daily mixed with the grain feed. For best results, these drugs should be given over a period of 6 weeks to 2 months. Prevention.—Preventive measures designed to control strongyles consist (1) in rotation of pastures, so far as possible, avoiding low and wet pastures, and (2) sanitation of stables to prevent larve from developing to the infective stage and from contaminating the feed and water. ‘This is accomplished by daily removal of manure from stables, supplying the feed in boxes and racks well raised above the floor, and supplying clean water. The disposal of stable manure is an important preventive measure, as is shown elsewhere in this circular. Little can be accomplished in the way of pasture sanitation except on farms where thoroughbred or other valuable horses are raised. On these farms the removal of manure deposits from. pastures may be practiced, as this procedure will remove almost all the parasite mate- rial before it can develop and spread. Such a procedure is necessarily troublesome and expensive and can be undertaken only by breeders to whom the question of expense is of secondary importance. The average breeder will have to resort to simpler and less radical measures, such as avoiding the overstocking of FIGURE 18.—Small strongyles of the horse pastures, frequent rotation of pastures, and special attention to foals. Where overstocking and the use of wet pastures are unavoidable, and rotation is impossible, reliance must be placed on treatment as often as necessary for control. Horse breeders, and even the general farmer, should pay consid- erable attention to the sanitation of paddocks in which the newly born foals are kept. The foals should be kept there for several weeks before they are put on pasture. Removal of manure from the paddocks, at least once a week, will cut down the supply of eggs and larvee to which the foals would otherwise be exposed. ‘This pre- caution will help to tide the foals over the most critical period of their lives. Young animals require special care much the same as children. Above everything else, a wholesome food supply and clean surround- ings are the best safeguards against disease. Special precautions to prevent foals from becoming parasitized are essential parts of sound management in horse-breeding establishments and on the average farm. THB SMALL STRONGYLES In addition to the blood strongyles or palisade worms, horses are commonly infested with numerous closely related species of stron- gyles, which are much smaller in most cases than blood strongyles, though some are almost as large. (Fig.18.) These worms occur in the colon and cecum and some of them produce visible injuries. One species, 7’riodontophorus tenuicollis, produces rather severe ulcers in the wall of the colon (Fig. 19), probably by means of the sharp teeth in their mouth cups. Some of the smaller horse stron- vyles, the many species known as cylicostomes, species of Trichonema 138442 °—37———_4 26 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE or Cylicostomum, are usually about a half inch or less in length and grayish white in color, and occur attached to the gut wall or free in the contents of the large intestine of the horse. These worms do not feed on blood, at least ordinarily, but they may feed on the mucosa of the large intestine. The immature forms of some cylicostomes occur in nodules in the wall of the large intestine. The small strongyles of the horse contribute to the picture of gross parasitism, and together with the large strongyles, are responsible for digestive disturbances, weakness, emaciation, and anemia resulting from severe infestations with parasites. The life histories of the smaller strongyles have not been studied in detail, but the indicated control measures with reference to these worms are the same as those recommended in connection with the control of blood strongyles. FicurE 19.—Lesions produced by one of the smaller horse strongyles: A, enlarged view of lesion with worms, Triodontophorus tenwicollis, surrounding it; B, types of lesions. (From Ransom and Hadwen, 1918) Treatment.—The treatments recommended for the removal of large strongyles are also used for the removal of small strongyles. Oil of chenopodium and normal butylidene chloride are especially effective against these worms. Carbon tetrachloride is less effective. PINWORMS The pinworms, Owyuris equi, which are commonly seen in horses are the females. These are relatively long, whitish worms with a very long and slender tail. (Fig. 20.) The males are small and inconspicuous and are seldom found. The females may attain a length of 3 to 6 inches. They occur in the large bowel. Life history—The gravid females pass out with the manure and then deposit their eggs, instead of depositing them in the bowel. Sometimes the females hang on to the anal opening and extrude their eggs in the region around the anus; the eggs may adhere in this PARASITES AND PARASITIC DISEASES OF HORSES Zi. region in the form of yellow crusts. In either case, the eggs develop outside of the body, as do those of the large intestinal roundworm, and in a few days they reach the infective stage. Each egg which develops normally contains a small worm within the shell. Ordi- narily the eggs do not hatch outside the horse’s body. Horses become infested with pinworms as a result of swallowing the infective eggs in feed or water. Symptoms and lesions—The most evident injury produced by pinworms is the irritation of the anus, which causes a horse to rub its tail and buttocks against any convenient object. This irritation may result from the passage of the worms out of the anus, from the crushing of the female worms as they pass out, or from some irritant property of the eggs. It is also reported that aside from causing this irritation, pinworms are responsible for digestive disturbances, and that, when present in large numbers, they produce anemia. If. reatment. —Oil of chenopodium, administered as for large stron- gyles, is effective for the removal of pinworms from the horse. Oil of turpentine is also an effective treatment and should be given in a dose of 2 fluid ounces (60 cubic cen- timeters) for a 1,000- pound animal, imme- diately preceded or followed by 1 quart of raw linseed oil or by the proper dose of the mixture of castor oil and neutral oil, as given under the treat- ment for large strongyles. Prevention. — Pre- ventive measures with FIGURE Bea OTE: Crue ised (females), of the reference to the con- trol of pinworms are similar to those recommended for the large intestinal roundworms and for blood strongyles. LUNGWORMS Lungworms, Dictyocaulus arnfieldi, are long, slender, whitish worms and range from about 1 inch to a little over 2 inches in length. They occur in the bronchi and in the bronchioles (branches of the bronchi). Life history—The egg contains an embryo at the time it is depos- ited by the female. The eggs hatch in the lungs, and presumably the larvee are coughed up, swallowed, and eliminated from the body with the manure. It is also likely that larve are expelled with mucus during coughing or sneezing. In either event, the larve undergo their development on the eround and attain the infective stage in a few days. On the basis of what is known regarding the method of infestation with closely related species of “lungworms 28 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE which occur in cattle and sheep, one may assume that horses be- come infested with lungworms as a result of swallowing the infective larvee with feed or water. Symptoms.—When few lungworms are present in a horse, definite symptoms are not produced. In heavy infestations the parasites produce bronchitis, and the most outstanding symptom of this con- dition is a cough. Excessive coughing weakens an animal, and in severe cases it may result in death. Treatment.—Medicinal treatment for lage ore infestation is unsatisfactory. Nursing treatment usually gives better results and is without harm to the animal. Nursing treatment consists in providing nourishing food, pure and uncontaminated drinking water, salt, clean, sanitary quarters, and adequate shelter. The affected animals should be re- moved from contaminated pastures and placed in lots or pastures which are not infested with parasite eggs and larve. This plan of treatment is designed to remove the animal from areas in which it is subject to gross : reinfestation and improve its condition. Prevention.—Preventive measures are similar to those recom- mended for the control of blood strongyles and the large intestinal roundworm. The manure must be disposed of in a manner that keeps the infective material away from the horse. THE NECK THREADWORM The large ligament of the horse’s neck, known to veterinarians as the ligamentum nuchae, is frequently parasitized by a long, slender threadworm, Onchocerca cervicalis. The exact length of these worms has not been determined owing to the difficulty of extracting them from the hgament without breaking them. Life history.—lt has been determined recently that certain biting flies, commonly known as midges, are the intermediate hosts of this parasite. The midges take up the larval worms in the course of piercing the skin of infested horses and, after a period of 24 to 25 days, the infested midges contain larvee capable of infecting suscepti- ble horses. Presumably, horses become infested as a result of being bitten by midges harboring the infective larvee Symptoms and. lesions.—These worms apparently act as irritants to the tissues and thus weaken their resistance to the attacks of dis- ease germs. There is reason to believe that this may lead to the de- velopment of poll evil and fistulous withers. Treatment.—Surgical and medicinal treatment may be employed where poll evil or fistulous withers is present, but there is no treat- ment for the destruction of the worms. Prevention —While it is difficult to prevent horses from being attacked by midges in localities where these pests occur, the avoidance of swampy pastures and of pastures which contain streams should prove beneficial in controlling the neck threadworm. THREADWORMS OF THE ABDOMINAL CAVITY Threadworms, Setaria equina, of the body cavity of the horse, also known as filarids or setarids, are relatively long and slender (Fig. 21) and occur in various locations outside the alimentary canal of the PARASITES AND PARASITIC DISEASES OF HORSES 29 horse. The filarid of the body cavity of the horse is from a little over 2 to about 5 inches in length and whitish in appearance and usually occurs in the abdominal cavity, but it has also been reported from other parts of the horse’s body. Immature forms of this filarid, as well as of the closely related filarid of cattle, sometimes occur in the eyes of horses as the so-called eye worm or “snake in the eye.” Life history.—The life history of this worm has not been definitely ascertained. From what is known of the life histories of related forms, occurring in other animals, it is probable that horse filarids are transmitted by blood-sucking insects. Symptoms and lesions —The adult worms do not appear to do much damage and are not known to be responsible for any definite symptoms. When the immature worms get into the eye, which apparently occurs only rarely in the United States, they produce con- siderable irritation and in time may produce blindness. Treatment.—The presence of this parasite in the abdominal cavity is seldom diagnosed dur- ing life and no treatment for it is known. When the worm is present in the eye, it may be removed surgically under local anesthesia. Prevention—In the absence of definite knowledge concerning the mode of transmis- sion of these parasites, no definite control measures can be recommended. Measures to prevent attacks by biting flies, the prevention of fly breeding, and the use of fly repellents are indicated as possibly of use, but less on account of this parasite than for other reasons. BOTS‘ B Bot re macoot Soave ; 9) FIcurRE 21.—Threadworms, Ss are £20 5 of certain flies (fig. 22) Setaria equina, of the known as botflies. Three species of bots abdominal cavity of the commonly occur in horses in the United States. pre* Naemmelei, 2 fe The common botfly, Gastrophilus intestinalis, occurs in practically all parts of the United States. The bots, or parasitic larve, are reddish in color and are attached to the white covering of the left sac of the stomach or along the ridge between the right and left sacs of the stomach. The adult fly deposits its eggs on the hairs of the inside of the front legs, breast, mane, belly, and even the hind legs. The throat botfly, or chin fly, @. nasalis, is rather widely distributed in the United States and is especially common in the Rocky Mountain region. The adult fly of this species deposits its eggs under the jaw of the horse, and in so doing causes much annoy- ance to horses. The bots are yellowish in color and are attached to that portion of the stomach which joins the small intestine and also to the wall of the upper part of the intestine. The nose fly, G. hemor- rhoidalis, has a more limited distribution than the other two species and is mostly confined to the North Central States and certain of the a eee ee eee ee *For more detailed information concerning horse bots and their pr i , Farmers’ Bulletin 1503, The Horse Bots and Their Control. PEs Gurwen eo tee 30 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE Rocky Mountain States, but it is spreading in all directions. The adult flies of this species deposit their eggs along the edge of the lips and cause much annoyance to horses. The nose fly is the most dan- gerous of the botflies and is the one which is responsible for many accidents because its annoyance makes horses panicky and causes them to run away. ‘The bots of this species occur in the stomach and duodenum, and when full grown also attach in the rectum. Life history.—The eggs are glued to the hair of horses by the adult flies. The eggs of the common horse bot are hatched apparently by the biting and licking of the horse, and are taken into the mouth on the lips and tongue. The small spiny bots burrow into the mucous membrane of the mouth, especially the tongue, where they remain from 21 to 28 days before emerging and passing on to the stomach. FIGURE 22.—Portion of a horse’s stomach, showing bots, Gastrophilus intestinalis, attached to the inner lining of the stomach wall. Natural size The habits of the nose bot are apparently very similar to those of the common bot. The eggs of the chin fly hatch without friction and the young bots crawl to and enter the mouth. Whether the throat bot penetrates the tongue is not yet known. When the bots reach the stomach they attach themselves to its wall and remain there for a period of from 8 to 12 months, during which time they attain their complete larval development and then pass out of the body. While the common bot and the throat bot pass out of the body directly with the manure, the nose bot reattaches itself to the rectum on its way out, then becomes detached and reattaches itself to the anus, where it may remain for three or four days, and finally drops to the ground. Usually all fully developed bots pass out of the body by October and those which overwinter in the horse are the young forms. These bots pupate in the ground and 20 to 70 days later emerge as PARASITES AND PARASITIC DISEASES OF HORSES 31 winged flies, ready to mate and to begin the process of egg laying once more. Symptoms and lesions —Bots often occur in large numbers, and it is not unusual to find several hundred of these maggots attached to the stomach wall of a horse. These parasites have large mouth hooks by means of which they attach themselves to the lining of the stomach and upper intestine. They also bear spines on much of their body surface. With this armature they are capable of irritating the lining of the digestive tract with which they are in contact and of producing considerable irritation and injury. The attachment of nose bots to the rectum and edge of the anus before they pass out is very annoying and horses have been known to dislocate bones in the tail in their attempts to obtain relief from this annoyance. The damage caused by the adult flies, especially the nose fly, is very great. Runaways may lead to serious accidents and farming is often interrupted by the inability to work the frightened horses. Treatment—Carbon disulphide is the most effective treatment for the removal of bots. Carbon tetrachloride may also be used but is much less effective. Both of these drugs should be used in accord- ance with the recommendations given under the treatment for large intestinal roundworms. In cases in which carbon disulphide is con- traindicated, tetrachlorethylene may be used. Tetrachlorethylene frequently will remove from 50 to 75 per cent of the bots when the drug is used in single doses of 1 to 2.3 fluid ounces (30 to 70 cubic centimeters) for a 1,000-pound animal after fasting the horse 18 hours. The drug should not be accompanied by a purgative. Cases of dizziness have been reported occasionally in horses dosed with tetrachlorethylene, but this dizziness soon passes off. Nose bots which have reached the rectum or anus are not amenable to these treatments. Treatment should be administered in the winter after the adult flies are killed by frost and all the bots are present in the stomach or upper part of the small intestine. One month before the internal medication an application of one of the coal-tar creosote dips in about 2 per cent dilution to the parts of the animal bearing the bot eggs is advised so as to destroy the eggs and thus avoid subsequent infestation. Prevention.—Preventive measures against infestation with bots include the use of various protective mechanical devices to prevent the flies from depositing their eggs on horses, shaving the hair where the eggs have been deposited, and the destruction of the eggs by certain medicinal applications to the skin. DISPOSAL OF MANURE Inasmuch as manure is the source from which horses acquire nearly all their common parasites, either directly or indirectly, the proper disposal of manure from stables and yards is an essential part of sound management. Indiscriminate spreading of fresh horse ma- nure on horse pastures to supply fertilizer is an unwise and unsafe procedure because it disseminates infective eggs and larve of para- sites which have developed in stables and yards. Owners of Thoroughbred horse farms who have learned of the danger to horses as a result of spreading fresh manure on pastures have discontinued this practice and are discarding manure as fertilizer altogether. 32 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE Such a procedure is too wasteful for farm practice, as the manure must be utilized and is safe after it has been stored for a time. Conditions of storage should permit the spontaneous heating process, which is destructive to eggs and larve of parasitic worms, to act throughout the manure for a sufficient time. When manure is stored in open piles it heats in the middle but remains cold on the surface. Such manure is dangerous, so far as parasite transmission is concerned, because the eggs and larve pres- ent on the surface of the manure pile escape destruction. It is, therefore, important that the outer 3 or 4 inches of exposed manure piles be turned over every week or so in order to bury the exposed manure under the inner material of the pile and sterilize it by heating. If this is not done, the manure should not be placed on any field to which horses may have access even months later, as the eggs and larve of many species of parasites are longlived and very resistant to unfavorable influences. It has been determined that the eggs and larve of parasites present In manure can be more certainly and easily destroyed if the manure is stored in closed containers - or boxes, having double walls and a double floor, with a 4 to 6 inch space between the walls and floor filled with sawdust, and the top of the container covered with a well-fitting lid. (Fig. 23.) It is essential that the containers be tight in order to retain as much heat as possible; the greater the heat developed and retained in manure boxes the sooner the eggs and larve will be destroyed. The sawdust acts as an insulator, but even with this precaution it is desirable to use tongue-and-groove lumber in the construction of manure containers in order to make them tight. Concrete boxes will not serve, as the manure at the sides is chilled and there is not heating enough to destroy parasites. For practical purposes manure which has been kept in such con- tainers for at least two weeks may be considered free from lving egos and larve of parasites and may be safely spread on pastures. Several manure boxes constructed on the above principles have been in operation at the Beltsville station of the Bureau of Animal In- dustry with successful results. These boxes have double-walled doors to facilitate the removal of the manure after it has been sterilized. In default of such measures, spread horse manure on fields which are to be pastured by animals other than horses, or plow it under. SUMMARY OF CONTROL MEASURES The most common and most troublesome parasites of horses in the United States live, at least part of their lives, in the digestive tract, either free in the lumen, attached to the walls, or embedded in the lining of the wall. These parasites produce eggs which pass out in the manure on to pastures, the floors of stalls, and other places. All such worm infestations in horses trace back to manure as the original source. Manure must be regarded as dangerous, and control measures should be designed to prevent contaminating the feed and water with manure so far as it is possible to do so. The following meas- ures are designed to reduce the possibilities of gross infestations of horses with parasites: PARASITES AND PARASITIC DISEASES OF HORSES 33 Pastures should be stocked lightly. Heavy stocking means more manure, and this, in turn, means a heavier concentration of parasite eggs and larve. Sloping hillside pastures are better than level ones. Rain and melting snow tend to wash manure down to some extent from sloping pastures. The bottom of a sloping pasture is dangerous because it has a high concentration of eggs and larve. It should be fenced off if possible. / \ / \ 1. eg ttt = A BMA NINN FIGURE 23.—A, Box with double walls and double floor for sterilizing horse manure; 8B, tight-fitting lid. The space between walls and floor must be filled with sawdust to insure insulation Rotation of pastures is desirable and should be used so far as available pastures permit. It is important to remember that perma- nent pastures perpetuate parasites. Stock rotation is a sound procedure. For the most part the parasites of cattle, sheep, and goats are not transmissible to horses, and vice versa. Move horses to a pasture on which cattle or sheep have been grazing and move cattle and sheep to a horse pasture in alternate years. 34 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE Keep stables clean; remove manure often, daily if possible; supply clean bedding and change it often; and supply clean water. Feed from boxes well raised above the ground and from overhead racks. Do not feed from the ground, because the feed will become contaminated with manure. Do not spread fresh manure on pastures. Hold stable manure, preferably in double-walled, closed containers, until it has under- gone a heating process. If you have an open manure pile, turn the outer few inches of the manure once a week. Bury it under the inner portion. If you have no facilities for keeping manure, haul it to areas used by animals other than those that produced the manure or plow it in for field crops. Take steps to reduce the fly nuisance by storing manure in closed containers or use flytraps or other preventive measures recommended by the United States Department of Agriculture. Remember that foals require special treatment to tide them over the eritical period of infancy. If you expect to raise sound horses, protect the foals. Consult a veterinarian when your horses require medicinal treat- ment for the removal of parasites, EXTERNAL PARASITES OF HORSES ® HORSE LICE Usually lice are restricted to one host species or to closely related species, and horse lice will not live on animals other than horses, mules, and asses. Three kinds of lice are commonly found on horses in the United States. The first and most important of these is the blood-sucking species known technically as Haematopinus asini. The two other species, 77ichodectes pilosus and T. parwmpilosus, are biting lice. The sucking louse of the horse is easily distinguished from the biting species. It is much larger and has a long, pointed head, whereas the biting lice have short, blunt, rounded heads. (Figs. 24 and 25.°) The sucking louse apparently causes more damage than the biting lice and it is more difficult to eradicate. NATURE AND HABITS The eggs or nits of the sucking louse are attached firmly to the hairs, usually close to the skin, and they hatch on the animal in from 11 to 20 days, the majority hatching in from 12 to 14 days. The young lice reach maturity and the females begin laying eggs when they are 11 or 12 days old. The lice pass their lives on horses, and can live only about 2 or 3 days when off a host animal. The biting lice of horses deposit their eggs in the same general manner as the sucking louse. The period of incubation is probably from 8 to 10 days. These lice may live as long as 10 days when separated from the host animal if kept on tufts of hair, but most of them die in 5 or 6 days. > By Marion Imes. ® From photomicographs by W. T. Huffman, of the Bureau of Animal Industry. i ¢ 4 PARASITES AND PARASITIC DISEASES OF HORSES do FIGURE 24.—Sucking louse of horses (Haematopinus asini): A, Male; B, female. (Magnified 25 times) FicurRE 25.—Biting louse of horses (Trichodectes pilosus): A, Male; B, female. (Magnified 25 times) & 36 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE During cold weather, when the hair on horses is long, lice increase very rapidly; but when the animals shed their hair in the spring the parasites seem to disappear. Some of the lice usually remain on the animals throughout the summer, but not in sufficient numbers to cause annoyance or to be easily detected. The animals, therefore, usually go into the winter infested. Since the most efficacious rem- edies are liquid dips, which can not be used safely on horses during cold weather, fall dipping should be practiced whenever horses have been lousy at shedding time. Symptoms.—The sucking louse obtains its food by puncturing the skin of the horse and sucking blood and lymph. When not feed- ing it moves about on the hair and skin. The biting lice do not suck blood from the host, but apparently feed on particles of hair, scales, and exudations from the skin. The irritation and itching which result from either or both methods of feeding are shown by the efforts of infested animals to obtain relief. Infested horses rub and bite themselves, and often kick and stamp and manifest extreme uneasiness and irritation. The coat becomes rough; the frequent rubbing destroys the hair in patches and often causes bruises or wounds in the skin. If lice are present in sufficient numbers to cause considerable itching and irritation they can usually be found, especially if the infested animal is placed in the sunshine. All species of horse lice are easily seen with the naked eye and often congregate in groups or colonies on parts of the animal. The favorite locations are the sides of the neck, around the flanks, and under the jaws. In cases of gross infestation, however, lice may be found all over the body and legs. When horses are lousy, close examination should be made to learn what kind or species of lice is present. It is not especially impor- tant, from a practical standpoint, to distinguish between the two species of biting lice, but it 1s important to know whether the ani- mals are infested with biting or sucking lice or with both kinds. Method of spreading—More cases of infestation originate from direct contact with lousy animals than in any other way. Under reasonably good sanitary conditions stables, yards, and other prem- ises which have contained lousy horses are not a source of great danger to horses free from lice. It seems probable, however, that occasionally lice may become dislodged from their host and drop on mangers, floors, etc., and from these locations find their way to a new host. When separated from their host sucking lice live about three days, the biting lice not to exceed 10 days. Ordinarily eggs are not de- posited except on the host, but when the hair to which they are attached is removed and kept under favorable conditions they may continue to hatch for as long as 20 days. The newly hatched lice live only two or three days unless they find a host. It is therefore possible for premises to remain infested for 25 or 30 days from the time they were occupied by infested horses. When lousy horses are clipped the hair should be burned and the ground or floor where the clippings dropped should be thoroughly treated with an insecticide. Lice may be carried from one animal to another on currycombs, brushes, and blankets, or by harness, saddles, and other equipment moved directly from a lousy horse to one free from lice. Curry- 3) e PARASITES AND PARASITIC DISEASES OF HORSES BY combs and brushes should be treated each time a horse is groomed. Harness, saddles, blankets, and other equipment used on lousy ani- mals should not be put on horses that are free from lice unless the equipment has been thoroughly cleansed. When cleaning stables and yards remove all litter and manure down to a smooth surface, then spray well with a good insecticide. The coal-tar cresote dips, diluted in accordance with the instruc- tions printed on the label of the container, are suitable for ridding premises of the lice. Treatment.—None of the dips recommended for use in treating horses can be depended on to eradicate lice at one dipping. The first dipping, if properly done, will probably kill all the lice, but it may not destroy all the eggs. The nits or eggs which survive dipping often hatch, forming a new generation of lice. This new generation should be destroyed by a second dipping after hatching is completed and before the young lice become mature and begin depositing eggs. Since these two periods overlap somewhat and vary greatly, and be- cause the periods from hatching to egg laying are different for the sucking and biting lice, it is impossible on this basis to calculate the exact period that should elapse between dippings. Young lice ap- pear on dipped animals as early as the third day after the first dip- ping, and since the average period of maturation is about 12 days it seems evident that the second dipping should be given in about two weeks. Experience has shown that two dippings with an interval of from 14 to 16 days usually can be depended on to control both sucking and biting lice. The dips commonly used for destroying lice on horses, mules, and asses, named in the order of their effectiveness, are arsenical solution, coal-tar creosote, and nicotine. ‘The arsenical solution is poisonous, and unless handled with due precaution injury to man and animal may result. When properly used, however, it is the most depend- able known dip for destroying lice. The coal-tar creosote dip is ef- fective when used in reasonably good water. ‘Two dippings, from 14 to 16 days apart, in either of these dips can usually be depended on to eliminate horse lice. Two dippings in nicotine solution will ordi- narily free horses from lice. On account of the difficulties in dipping in cold weather, and the unsatisfactory nature of hand treatments, most of them only palliative, it is advisable to dip for lice, when they are present, in the fall of the year before the onset of cold weather. Hand applications of dusting powders and oils and greases are often resorted to in treating horses for lice. Some of the dusting powders are of value in holding the parasites in check, but, as a rule, they are not effective in controlling sucking lice. Biting lice can be destroyed with sodium fluoride applied in the form of a powder or mixed with water in the proportion of about 1 ounce to 1 gallon; but sodium fluoride is not effective against sucking lice. Care should be taken not to apply sodium fluoride too freely around the natural body openings or where the skin is very thin and hairless, and not to rub it into the skin. It may be applied with a dust gun, or a shaker, or by hand. : Oils and greases, such as crude petroleum, crank-case oils, or equal parts of cottonseed oil and kerosene, are effective remedies for lice; but ordinarily they are not suitable for use on horses, as they cause the hair to come out, and they often blister the skin. 38 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE Fumigating horses with the fumes from burning sulphur (sulphur dioxide) will kill horse lice, but many of the eggs survive, and two treatments two weeks apart are necessary to effect eradication. The advantage of this method of treatment is that it can be used when the weather is too cold for dipping. The disadvantages are that it is necessary to have a gas-tight inclosure and the animal’s eyes and nostrils must be kept away from the gas.