Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practice: CIRCULAR No. 148 ..,4-- mI m5 : Issued November, 1930 Washington, D. C. Revised January, 1933 Parasites and Parasitic Diseases of Horses By BENJAMIN SCHWARTZ Senior Zoologist MARION IMES Senior Veterinarian and WILLARD H. WRIGHT Associate Veterinarian Zoological Division, Bureau of Animal Industry yee Si ‘Has been reve “=—See rev e@de binders at e file. end of ISSUED NOVEMBER, 1930 REVISED JANUARY, 1933 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. CIRCULAR No. 148 PARASITES AND PARASITIC DISEASES OF HORSES’ By BENJAMIN ScHWARTzZ, Senior Zoologist, MARIon IMEsS, Senior Veterinarian, and WILLARD H. WricuT, Associate Veterinarian, Zoological Division, Bureau of Animal Industry CONTENTS - Page Page Internalsparasites Ol NOrses=sasen eee 1 | Internal parasites of horses—Continued. Abundance and location_________________ 1 DIS DOSALVO fad AMULET Sere nee eee 31 Symptoms and damage produced by Summary of control measures____________ 32 DATASILCS ae tie ke eS hy PA ae ee 1 | External parasites of horses__________________ 34 General control measures________________ 2 EORsepliceesss 2 ae P18, iN ae 34 Medremalitredtim ents ne ee 3 FEV OUSC SINT) FC ees Ss area eee eee 38 IETOCLOZOd kas Sree Ses) as yee eae 4 BURT CK Que = cB E Aces Us MA pr ReGen eat ee es at 45 or DATASITES ee oe oe 4 Treating horses for external parasites__- 48 OLS ee es irs at ees ASO RSS ct 29 INTERNAL PARASITES OF HORSES? ABUNDANCE AND LOCATION HE TERM PARASITE as used in this circular refers to forms 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. Al 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 cf 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, 153249°—33 1 2 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 an1i- 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- ditions 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 larvee 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 lkewise 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 pr esent. 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 1rT1- 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 is 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 pr escribed 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 para- sites in the late spring or early summer and in the fall, and for bots in late November or December and again in February, if necessary, to remove those which have developed since the first treatment. In the South, owing to the shorter and milder winter and the more abundant warmth and moisture, it may be necessary to treat oftener. Judgment, based on experience, is a better basis for procedure than any general rule. Internal 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 As already stated, 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 ’ Information 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 fiukes 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. i 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 314 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 Figur 1.—Almost a gallon of large tapeworms, Anoplocephala magna, removed post- mortem from a horse. About one-half natural size. (Photograph by courtesy ot 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- Ficurn 2—The dwarf lowing treatments have been recommended but « . f y Pe 5 «eye . . Pies HRPM aI have not had critical test to determine their pre- the horse. Natural cise value. Fe 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. PARASITES AND PARASITIC DISEASES OF HORSES | 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 (380 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 given 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 linseed oil. The foregoing drugs should be used with caution and given only to animals in ood 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 eges and larvee 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 occurr ing 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 deposited 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 of the stomach wall, for which tumors these worms are respon- sible. One species, Carter’s stomach ; worm, Habronema muscae, of the horse, is from about one-third \ \ inch to nearly an inch _ long. This parasite occurs free in the stomach or attached to the wall of the stomach. A second spe- cies, the small-mouthed stomach worm, H. microstoma, is similar in size and appearance to the above species. While this form may occur free in the stomach, it A is capable of penetrating the wall of this organ and causing sores. Ficurn 3.—Large stomach worms of the A third species, the large- horse. the mmariire arid aevelap Se on Me Ground and © — OV? DASTUPCE. 83 , s NH haer yavoratble CONAHIONS ThE EGGS reach whe yective stage 117 about 4WO WEEKS. ~The rare WOTIS wn he intestines ay VROUSOVIDS SP EGGS. Horses becorze ifested as a rest!? of swaliain Wfective eggs with JOO" Of waver 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 PARASITES AND PARASITIC DISEASES OF HORSES ao ; ; ies as10q B JO Apod oy} Ysnory AouAnOol splivose sy y—'s AYA SS ( tonaas ) ‘aNnouo (iON SES) GaEES EI (8G AHL NO S993 SHL JGISNI WHOS doo1g Ni 1YV3SH SHL OL OO a SNHOM ONNOA SW3SM M34 V NI SWHOM ONNOA YaAM WoUs Loma | = (s) (©) oS yu Ny LION & t cl a ( 8'ON Bas ) ve. "ANNOYS SHL OL WIV4 ONY a = SYNNVW NI AdOg 3O LNO RRORTEES = SSVd ‘SSNIISSLNI NI SAHOM YyaONVT] SSWIL TWusAaS MONO 4 = Slag DviNead Cao ndesdssoos GNV S7SSS3A Goold NI SONM OL S..5 { 09 SWHOM ONNOA ‘LYV3H WouS BS \ © () fe (€'0N 33s) oe S1assaA Goold NI Y3AI ee \\ OL 0D SWHOM ONNOA GNV SANISALNI NI HOLVH S993 ( 9'ON 33s ) GAMONIVWMS S3YV GNV HLNOW 30 MOVE O.LNI AdIdGNIM dN IMVYO SWYOM ONNOA ‘SONN1 NI SAVO MSs V YS1SV ea — | ( ZON 33s) aamomvmMs | GNV GNNOYS Wows dn l G3ayold J3YV SWHOM ONNOA | ONINIVLNOD S993 WHOM | | | ( 2°ON 33S) ‘S903 40 SNOITMIW 3ONdOud GNV SSNILSSLNI NI SAIN OL SNNILNOO ASHL “SHLNOW 2 LNOGV NI ALINALVW OL MOUS ‘GaMOTNIVMS 3YV GNV SONAT HONOYHL GAaSSVd JAVH LVHL SWHOM ONNOA © Fats and oils should be avoided as they promote the absorp- tion and increase the toxicity of the car disulphide usually produces a limited area o ment. 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. S. DEPARTMENT OF AGRICULTURE from 6 to 12 fluid drams (25 to 50 cubic centimeters) for a 1,000- pound animal. This drug does not need to be: accompanied with a purgative, but it is usually advisable to give purgatives, in this case salts, with carbon tetrachloride for removing worms. 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, and preferably longer. The stable and paddock in which the mare and foal are kept should be cleaned often, daily if possible, ht- ter and manure being removed. These precautions are designed to pre- vent the foals from becoming heavily in- fested with ascarids at an early age, and before they have de- veloped the necessary reserve vitality to cope successfully with a heavy worm infestation. When the foal is moved to a pasture it is essen- tial to select one which is clean and that has not been used by horses for a vear or _ longer. Horses may be moved to cow and Figure 9.—Type of insanitary box stall. Note accumu- sheep oS TTEES and ™ "ation of litter’ and manure vice versa, because parasites of rumi- nants are not transmissible to horses, and equine parasites are not transmissible to cattle and sheep, as a rule. Proper disposal of manure, and sanitary measures 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 17. 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 larve 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. Asa 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, 153249°—33 a vo 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 larve, 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 larve 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- tures and in their Rroume 11 EDS ok anita, bok eral Nee Fete alla egies 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.—Nothing 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- 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 Ficurp 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 SNS. equinus; the small 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. 18, C), is from about 114 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 ina 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 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, S. equinus. Enlarged. From Looss, 1901 protection to the eggs and larve and it is likely that direct sunlight 1s 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 larvee 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 PA 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 larvee 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. a Lygs reach the pasture With the (71000 C aI develgp i abou a day Or Two Urider- < Javoratle £998 HiTol 07 Ly VOOSTUPE G1 THE cong Hors: larvae (a) develop yo the ifectwe stage (bl) 17 Ob0U7 @ Wee OF 70 Va Vile WOCTIS in digestive tract of He horse lay (nay €2G5. fipective larvae chink up blades Sf VOSS 177 wer wedlnary, “oe 3 as a restilt OF sHallonirg UY ECTIVE 180 VAE HL YI AES, Ficgurn 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 lhning. 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 Figure 15.—Section through the wall of the large gut, stretches consider- showing the head end of an attached blood strongyle, S. equinus, with a tuft of the inner lining of gut drawn ably to form what Se 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 23 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. If the 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 lining FicurE 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 shght 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- eresses 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.—lIt 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 ta 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 oil, 1 pint; for yearlings and 2-year- olds, castor oil, 6 to 8 ounces, and neutral orl, 1 pint ;: for. 3- year-olds and older, castor oil, 8 to 10 ounces, and neutral } oil, 1144 pints. FIGURE 17._—Horse suffering from gross infestation with . Carbon tetrachlo- parasites (strongylidosis). Note marked emaciation. ride is also of value Following treatment for the removal of parasites, this TSE Hn een ea for the 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 1s 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 probable 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, treatment may be re- peated in from four to six weeks. 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 PARASITES AND PARASITIC DISEASES OF HORSES 25 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 pastures, frequent rotation of pastures, and special attention to foals. Where over- stocking 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 considerable 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. The removal of manure from the paddocks, at least once a week, will cut down the supply of eggs and larve to which the foals would otherwise be ex- posed. This precaution will help to tide the foals over the FicurE 18.—Small strongyles of the horse. ate 2 = The larger forms are Poteriostomum species most critical period of their and the smaller ones are cylicostomes. : Natural size lives. Young animals of all sorts are special cases and require special care. In the last analysis the saving of young livestock involves the same precautions which are used in connection with the prevention of sickness in children. Above everything else, a wholesome food supply and clean surroundings 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. THE SMALL STRONGYLES In addition to the blood strongyles or palisade worms, horses are commonly infested with numerous closely related species of stron- glyes, 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’iodontophorus 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- gyles, the many species known as cylicostomes, species of Trichonema f53219°= 33-4 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 tenuicollis, 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, Oxyuiis egui, 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 eges in the region around the anus; the eggs may adhere in this PARASITES AND PARASITIC DISEASES OF HORSES gov region in the form of yellow crusts. In either case, the eggs develop outside of the body, as do those of the large intestinal roundwor m, 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 irr itant 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. Treatment—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 PD NOT, Oratrts Cathe (femaies), 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 larve are coughed up, swallowed, and eliminated from the body with the manure. It is also likely that larvee are expelled with mucus during coughing or sneezing. In either event, the larve undergo their development on the round 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. So far as is known, lungworms are not very common in horses in the United States, and as a rule the infestations when present are not very severe. Treatment—Medicinal treatment for lungworm infestation is un- satisfactory. Many drugs have been advocated for injection into the trachea or windpipe but there is little evidence to indicate that such drugs actually kill the lungworms. On the other hand, considerable damage to the delicate lining of the air passages may result. 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 Jarve. This plan of treatment is designed to remove the animal from areas in which it is subject to gross reinfestation, to improve its condition, and to tide it over the more critical period of the disease while it builds up its resistance to the lungworms. 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. THH 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 trom the ligament without breaking them. Life history—The life history of this parasite has not been as- certained. 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 —In the absence of information concerning the life his- tory of these parasites no definite measures can be recommended. THREADWORMS OF THE ABDOMINAL CAVITY Threadworms, Setaria eqguina, 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 A x 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 B indicated as possibly of use, but less on account of this parasite than for other reasons. BOTS * Beis are maggots of certainties (fg, 22) "reves 21-7 Tcadworae known as botflies. Three species of botflies abdominal cavity of the occur in horses in the United States. fie eee aes 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, G. 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 *For more detailed information concerning horse bots and their prevention consult Farmers’ Bulletin 1503, The Horse Bots and Their Control. 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 torun 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. Be 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 living eggs 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 oo 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. AOR > J+ // LT. ies hams N —— \\ \\ N FicurE 23.—A, Box with double walls and double floor for sterilizing horse manure; B, 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. §. 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 critical 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, 7’7ichodectes 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. 5 By Marion Imes. ; 6From photomicographs by W. T. Huffman, of the Bureau of Animal Industry. PARASITES AND PARASITIC DISEASES OF HORSES 35 FIGURE 24.—Sucking louse of horses (Haematopinus asini): A, Male; B, female. (Magnified 25 times) Figure 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 is 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- PARASITES AND PARASITIC DISEASES OF HORSES ai 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, 1f 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. A concentration of about 1 per cent sulphur dioxide is necessary to kill the parasites, and serious injury or death may result if the gas comes in con- tact with the eyes or nostrils. After fu- migation it is neces- sary to hand treat that part of the head that was not fumi- gated. (Fig. 26.) HORSE MANGE Scabies in_ horses, commonly known as mange, itch, or scab, is a name given to a group of contagious skin diseases caused by minute parasites Inown as mites, which live on or in the skin. Tour species of these parasites are found on domesticated animals, but horses are com- monly affected by only three of them. These parasites are classified zoologically in three different genera — Sarcoptes, Psoroptes, and Cho- rioptes. Mites of the FIGURE 26.—Fumigation with sulphur gas for lice. Eyes first two genera are and nostrils must be kept away from the gas. Part of bere : head not fumigated must be hand treated — shown in Figures ai and 30. In obtaining their food from the host and preparing a resting place in or on the tissues, the mites cause wounds or lesions in the skin. As each kind of mite possesses distinctive habits, the location and nature of the lesions in the early stages are more or less charac- teristic. Each kind of mite, therefore, causes a specific kind of mange which is named after the generic name of the mite. Thus we have in horses sarcoptic, psoroptic, and chorioptic mange. The sar- coptic variety is the one most common on horses in the United States. PARASITES AND PARASITIC DISEASES OF HORSES 39 SARCOPTIC MANGE SARCOPTIC MANGE MITE The mites which cause sarcoptic or common mange of horses are small, white, or yellowish parasites known technically as Sarcoptes scabiet equi. (Fig. 27.) The female when full grown measures about one-fiftieth and the male about one-sixtieth of an inch in length. When placed on a dark background they are visible to the naked eye. The general form of the body is more nearly round than oval, and the bluntly rounded head is as broad as it is long. When mature, these mites have four pairs of short, thick legs, the fourth pair and usually the third pair also not extending beyond the margin of the body. Under a high-power miscroscope a number of short, backward-projecting spines may be seen on the upper surface of the body. The sarcoptic mites penetrate the upper layer of the skin and exca- vate burrows or galleries in which the mating of the sexes occurs and the eggs are laid. Each female may lay from 10 to 25 eggs during the egg-laying period, which probably lasts from 12 to 15 days. When that period is completed the female dies in her burrow. The entire life cycle is passed on the body of the host animal. The eggs hatch in from 3 to 10 days, and the young mites after passing through several molts reach maturity and begin laying eggs in 10 or 12 days. As the average period of incuba- : tion on the animal is about four paamaie” a (cated (00 cee days, and the average period after hatching until egg laying begins is about 11 days, a new generation of mites may be produced in about 15 days. If the first treatment or dipping could be depended on to kill all the mites on the animal the time for the second treatment could be calculated accurately. Jnfortunately, the first treatment usually does not kill all the sarcoptic mites on the animal because of the difficulty of getting the dip or other insecticidal substances into the burrows and in contact with the mites. Practical experience has shown that the interval between treatments or dippings should be from five to seven days. Symptoms.—tin the early stages of sarcoptic mange in horses the first visible lesions usually occur on the neck or shoulders or around the head, but the disease may start on the breast, flanks, sides, or other parts of the trunk. From these parts the disease spreads until the entire surface of the body may become involved. ‘The mites penetrate the upper layer of the skin, each female making a separate burrow or gallery, which usually extends to the sensitive tissues or “ quick.” The presence and activities of the mites A() CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE on the sensitive tissues cause great irritation and itching, and the skin becomes inflamed and swollen, so that small nodules are formed over and around the burrows. As the disease developes vesi- cles are formed which break and discharge serum. As the serum dries, small scabs are formed, and the hair over the affected parts stands erect and some of it drops out. In some cases the affected areas of skin become dry and scurfy, and may have a leatherlike appearance. (Fig. 28.) The mechanical injury to the skin resulting from rubbing and biting causes large scabs to form, which adhere firmly to the under- lying tissues. The large scabs often are broken by the movements FIGURE 28.—Sarcoptic mange. Head, neck, and shoulders involved of the animal, and blood or serum may stain the scabs a reddish vellow. As the disease advances the skin becomes more or less bare in ir- regular-shaped, bald patches, and is greatly thickened and thrown into wrinkles or folds. (Fig. 29.) In severe cases the horse loses fiesh rapidly, becomes greatly weakened, and unless properly treated may die. 3 Contagiousness.—Sarcoptic mange is transmissible from one spe- cies of animal to another, and also from animals to man. Ordi- narily when one species of animal contracts the contagion from an- other species the mites live only a limited time on the new host. Sarcoptic mites of the sheep, hog, camel, dog, cat, and rabbit may PARASITES AND PARASITIC DISEASES OF HORSES 41 live on horses, and those of the horse, dog, and hog are known to be readily transmissible to man. Sarcoptic mange of horses is contagious to all classes of horses and is usually transmitted by direct contact with infested animals. It may, however, be transmitted by other objects, such as currycombs, blankets, or harness, or in stables or other premises. It is important that mangy horses be isolated and all equipment kept separate until the disease is eradicated. Apparently the disease spreads slowly during warm weather, especially among horses on pasture, but it makes rapid headway in horses closely confined or crowded together in small inclosures. Exposure to cold, inclement weather, insufficient feed, or feed of poor quality, or any other circumstances tending to lessen the vitality or functional activities of horses hastens the spread and development of mange. When the mites are active under favorable conditions the FIGURE 29.—A well-advanced case of sarcoptic mange lesions extend rapidly, and the entire body surface may become involved in about six weeks. . Although they do not propagate themselves except on the bodies of animals, the mites as well as their eggs may retain their vitality for a considerable time off the host animal. When exposed to sun- light in dry places the sarcoptic mites live only a few days, but in moist, protected places they may live three weeks or even longer. Although it is difficult to infect horses experimentally from infested premises, the possibility that the disease may be contracted from such sources should not be overlooked. It is good sanitary practice to clean and disinfect all stables and small inclosures which have been occupied by mangy horses, also all currycombs, brushes, blan- kets, and other objects used on such horses, before using them for clean animals. Cleaning and disinfecting for sarcoptic mange may be done in the same manner as for lice. Treatment—On account of their burrowing habits, sarcoptic mites are difficult to eradicate. The common dips, such as lime- 42 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE sulphur, nicotine, and coal-tar creosote, will kill sarcoptic mites if the dip can be brought into direct contact with the parasites. This method, however, requires thorough, frequent, and persistent applica- tions. From four to six dippings, five to seven days apart, in lime- sulphur or nicotine solution will usually effect a cure‘in ordinary cases, especially if all affected areas are soaked well with warm dip and scrubbed with a brush just prior to the first dipping. Affected animals should be held in the bath from two to three minutes. Two or more applications, a week apart, of unprocessed crude petroleum will usually eradicate sarcoptic mange, if treatment is applied before the disease becomes chronic. Crude oils, however, often cause the hair to come out and may blister the skin. Crude oil is not a suitable dip for common use on horses, but it is of value in hand treatment for holding mange in check during the winter months when the temperature is too low for dipping. Crank-case drainings may be substituted for crude petroleum, but such oils also cause loss of hair and often blister the skin. Fumigation of mangy horses with sulphur dioxide has been recom- mended by some European investigators. The Bureau of Animal Industry has conducted some field tests with this method of treat- ment, but the equipment and methods of application so far devised are too complicated and expensive for general use except where large numbers of horses are assembled for treatment under the supervision of a veterinarian. Apparently this method of treatment has no dis- tinct advantage over dipping except that it can be used when the temperature is too low for dipping. In applying home treatment or fumigating for mange the medicament has a better chance of reach- ing the parasites if the hair over and around the lesions is first clipped and singed. Cases of sarcoptic mange of long standing, which have been neglected and allowed to develop until the affected skin has become greatly thickened and leatherlike, are usually incurable by any ordi- nary method of treatment. In cases of suspected mange prompt and vigorous action should be taken, as the disease can be eradicated in the early stages at comparatively low cost. PSOROPTIC MANGE PSOROPTIC MANGE MITE The mite (Psoroptes communis equi) which causes psoroptic mange lives on the surface of the skin and does not form burrows. Psoroptic mites are slightly larger than sarcoptic mites, the mature female measuring about one-fortieth and the male about one-fiftieth of an inch in length. (Fig. 30.) The entire life cycle is passed on the host animal. Each female may deposit from 15 to 24 eggs, which hatch in three to four days. The young mites reach matur- ity, mate, and the female deposits eggs in from 10 to 12 days. Dipping, if properly done, kills all psoroptic mites, but can not be depended on to destroy the eggs. Some of the eggs may hatch after dipping, thus forming a new generation of mites. To effect eradica- tion it is necessary to give a second dipping after hatching is com- pleted and before the young mites reach maturity and begin laying eggs. It is evident that the interval between the first and second dip- pings should be from 10 to 12 days. PARASITES AND PARASITIC DISEASES OF HORSES 43 Symptoms.—Psoroptic mange may start on any part of the body: covered thickly with hair, but the first lesions usually appear on the head under the foretop, on the top of the neck around the mane, or on the rump. From the starting point the disease spreads slowly over the body. The mites prick the skin and probably introduce a poisonous se- cretion into the wound. A slight inflammation is caused, accom- panied by an intense itching. In the early stages of the disease the lesions are not sufficiently prominent to attract attention, but the animals rub and bite themselves to relleve the intense itching, and these symptoms should always be in- vestigated to learn the cause. As the mites multi- ply, large numbers of small wounds are made in the skin, fol- lowed by the forma- tion of papules, in- creased inflammation and itching, and the exudation of serum. The serum which oozes to the surface becomes mixed with foreign matter and microorganisms, and this mass soon hard- ens into yellowish or eray-colored scabs. The scabs are fre- quently stained with blood. In the early stages the _ hairs around the lesion aay. be glued ie Figure 30.—Psoroptic mange mite. Female. (Magnified gether in a_ small 100 times) clump and the nodule or scab may be about the size of a pea. As the mites constantly seek the healthy skin around the edges of the wound, the scab or lesion gradually increases in size. Some of the mites migrate to other locations and start new lesions, which extend until they cover large areas. As the disease advances the skin becomes thickened, tumefied, and thrown into wrinkles or folds. Large areas become denuded of hair and covered with thick, adherent scabs. When the disease reaches this stage it is difficult to differentiate it from sarcoptic mange. Itching is intense and irritation continues throughout the course of the disease. The skin becomes bruised and raw from the reck- less rubbing against any available surface. The uniform thickening 44 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE and hardening of the skin is characteristic of mange, but the most certain diagnosis consists in finding and identifying the mite which causes the disease. In the early stages of psoroptic mange the mites may usually be found in scrapings taken with a blunt-edged knife from around the edges of fresh lesions. In the advanced stages scrapings taken from the edges of scabs or from the bottoms of the folds of skin may contain mites. In the early stages psoroptic mange may be distinguished from sarcoptic mange by the character of the lesions and the manner of spreading, but the most dependable diagnosis consists in finding the mite. For practical purposes where facilities for examination are limited the principal differences in form and structure of the two species of mites may be summarized thus: The sarcoptic mite is slightly smaller than the psoroptic mite, and the body of the former is more nearly round than oval. (Fig. 27.) Adults of both species have four pairs of legs, those of the psoroptic mites being long, and all four pairs extend beyond the margin of the body. (Fig. 30.) The sarcoptic mites have shorter legs, and the fourth or hind pair and usually the third pair do not extend beyond the margin of the body. The head of the common scab mite is tapering or cone-shaped and is longer than it is broad, whereas that of the psoroptic variety is bluntly rounded in front and is as broad as it is long. It is advisable to examine several specimens in all cases, because under low-power magnifying glasses the females of the two species are more easily distinguished from one another than the males. On account of the burrowing habits of the sarcoptic mites, they are difficult to find, especially in the early stages of the disease. They are situated in burrows under conical papille, and by scraping the infested area until the blood oozes from the tissue, the mites some- times may be found in the scrapings. Contagiousness.—Each species of domesticated animal has its own pecular variety of psoroptic mange, and the variety which lives on the horse, ass, or mule is not transmissible to other animals, with the possible exception of the camel. The disease is more highly con- tagious to all classes of horses than sarcoptic mange. The predis- posing causes, manner of spreading, carriers of the mites, and pre- cautions to be observed in isolating infected animals and cleaning and disinfecting premises are practically the same as for sarcoptic mange. Treatment.—As the psoroptic mites live on the surface of the skin, they are more easily eradicated than the sarcoptic variety. The rem- edies recommended for sarcoptic mange are effective in eradicating this disease. Two dippings from 10 to 12 days apart may usually be depended on to cure ordinary cases. Four or more dippings may be necessary in chronic cases. CHORIOPTIC MANGE CHORIOPTIC MANGE MITE Chorioptic or symbiotic scabies, commonly known as foot mange, is caused hy a mite (Chorioptes equi) which closely resembles the PARASITES AND PARASITIC DISEASES OF HORSES 45 psoroptic mite. Chorioptic mites live on the surface of the skin and produce lesions similar to those of psoroptic mange. The lesions of chorioptic mange are usually confined to the lower part of the limbs around the foot and fetlock: Occasionally the mites spread over the legs above the hocks, and may reach even the thighs and abdomen, but usually the disease remains localized around the feet. Infested animals paw and kick and rub the pastern with the oppo- site foot and often try to bite the affected parts. Some of the hair comes out and the skin has the thickened and hardened condition characteristic of scabies. The remedies recommended for sarcoptic mange are effective in eradicating foot mange. The affected areas should be well soaked in warm lime-sulphur dip, and the treatment repeated every 10 days until a cure is effected. Driving the horses through a shallow wad- ing tank filled with dip is a quick and effective method of treatment for foot mange. TICKS There are many different kinds of ticks which may attack horses, but since the habits and life cycles of the different species vary greatly discussion in this circular is necessarily hmited to general information, except for the ear tick, which is discussed more fully. When only a few ticks are found on horses they may be removed by hand or covered with crude petroleum, cylinder oil, kerosene, or other oil, which usually causes them to detach and drop to the ground. In removing ticks by hand the writer has observed that they may sometimes be detached without leaving the head embedded in the skin by twisting them around as they are pulled loose. In the southern and western parts of the United States it is not uncommon for horses to become grossly infested with ticks. In some sections the infestation may occur only infrequently; in others it may occur more or less regularly each year. In the region in- fested with cattle-fever ticks where eradication work is in prog- ress tick-infested horses are dipped in arsenical solution to kill the parasites. In any locality where the horses become infested with ticks and the infestation is extensive the State livestock sanitary authorities should be notified in order that the ticks may be identified and proper measures taken for control. Control or eradication methods to be successful must be based on a knowledge of the life history and habits of the tick involved. SPINOSE EAR TICK Nature and habits—The spinose ear tick (Ornithodoros méqgnint) is prevalent on horses in the Southwest and causes serious damage to the livestock industry. Spinose ear ticks (fig. 31) enter the ears of animals as small, 6-legged seed ticks and attach themselves in the external canal well below the hair line, where in a week or two they become engorged larve. The engorged larve molt to form nymphs or young ticks having eight legs. The young ticks remain in the ears from one to seven months, or until fully grown and engorged, 46 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE FIGuURD 31. gorged larva (magnified 5 times) ; C, young tick (magnified 5 times); D, partially engorged young tick (magnified 5 times); #, fully engorged young tick (magnified 5) times) ; F, adult female (magnified 5 times) ; G, adult male (magnified 5 times) A, Ear ticks and débris from ear of animal (about natural size); B, en- PARASITES AND PARASITIC DISEASES OF HORSES 47 when they drop to the ground, crawl up into dry, protected places above the ground, and again molt. The skin of the nymph is covered with spines, but that of the mature tick is smooth. So far as is known the adult tick does not attach itself to animals nor does it take food. Mating and egg laying take place off the animal, and when egg laying is completed the female dies. The eggs may hatch as early as 10 days after they are laid. Shortly after hatching the seed ticks are ready to attach themselves to any suitable host. They may live as long as three months if no host is found. ; Symptoms.—W hen animals are grossly infested and the ear canals packed full of ticks the parasites are visible on superficial examina- tion, but when the degree of infestation is hght or moderate the ticks may be overlooked. They usually attach themselves in the deep folds of the ear or crawl into the ear canal and follow it inward, sometimes as far as the eardrum. As the ticks increase in size and others enter, they and the excretions, with the wax from the ear, accumulate in masses or plugs sufficient in some cases to close up the ear passages completely. These conditions give rise to various symptoms. The infested animal usually shakes its head and re- peatedly turns it from side to side, meanwhile inverting, or turning down, first one ear and then the other. When irritation and itching are more intense on one side the animal ay -% often turns its head : Z arse coneibatietmore seta ee riously affected ear Figure 32.—Ear probe made of baling wire is held downward. There is a tendency to rub and scratch the ears, and young animals often run as though endeavoring to relieve the nervous tension. In all cases where ear-tick infestation is suspected the animals should be examined, and if no ticks are visible the ears should be probed. A convenient and effective instrument for probing the ears. removing ticks from the ear canals, and breaking down masses of ear wax and ticks may be made from a piece of ordinary baling wire, as shown in Figure 32, the loop end being used for dislodging the ticks. Treatment—Complete eradication of spinose ear ticks is a diffi- cult matter, on account of the habits and great vitality of the ticks and the wide range of animals which they may infest. Results of investigations conducted by the Bureau of Animal Industry have shown that dipping in any of the known dips or the injection into the ear passages of bland oils, crude petroleum, or various dips, etc., is not effective in killing the ticks or causing them to leave the ears. Gasoline and kerosene when applied undiluted kill the ticks, but cause blistering of the skin and are not suitable for use on horses. Chloroform, undiluted or mixed with a bland oil, is commonly used on horses and dogs and is effective. Such substances as chloroform evaporate rapidly, and therefore afford no protection against reinfestation. The remedy for ear ticks formulated and thoroughly tested by the Bureau of Animal Industry consists of a mixture of two parts by volume of ordinary pine tar and one part by volume of cottonseed oil. In mixing the ingredients add the cottonseed oil to the pine tar 48 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE and stir until a uniformly smooth mixture is obtained. When neces- sary the ingredients should be warmed before mixing, so that they will mix readily and flow freely. The mixture remains uniform without separation or deterioration, and may safely be used on any species of domesticated animal. Being of a sticky consistence, it remains in the ears and affords protection against reinfestation from 30 to 60 days. The only known effective method of applying treat- ment is to inject the remedy into the ear passages by hand. Most horses oppose the insertion of anything into their ears, and some form of restraint is necessary. Gentle farm horses can usually be controlled with the twitch or other well-known methods of re- straint, but in treating wild range horses special equipment is neces- sary. An ordinary crowding chute not more than 3 feet wide is suitable for treating horses for ear ticks. An ordinary metal or hard-rubber syringe holding from 1 to 2 ounces is the best instrument to use for injecting the pine-tar-cot- tonseed-oil mixture. Have the mixture warm enough to flow freely, fill the syringe, grasp the ear with the left hand, then insert the nozzle into the opening of the ear canal and inject about one-half ounce of the fluid. Hold the ear in an upright position for a few seconds and manipulate to force the mixture into the deeper parts. If too much fluid is injected it will overflow and run down over the head and face, where it may cause blistering. The mixture causes very little irritation except on parts exposed to the direct rays of the sun. When the ear passages contain masses of hard wax and ticks, such masses should be broken down and scraped out with a wire loop before treatment is applied. Treatment should be applied as often as necessary to keep the ears free from ticks. One treat- ment properly applied can be depended on to kill all ticks in the ears and to prevent reinfestation for about 30 days. It should be re- membered, however, that the eggs of the tick are not deposited or hatched in the ears of animals, and a new crop of seed ticks may find lodgment at any time on animals kept in infested places. TREATING HORSES FOR EXTERNAL PARASITES The three commonly used methods of treating horses, mules, and asses for external parasites are (1) hand applications, (2) spraying, and (3) dipping. A fourth method, not in common use but recom- mended by some European investigators, is fumigation with sulphur dioxide. HAND APPLICATIONS Infested animals may have parasites on any or all parts of the body surface, and to effect complete eradication usually it is neces- sary to cover the entire surface of the skin with the medicament. On account of the difficulty of applying treatment by hand over the entire body surface, hand applications are recommended only as a temporary measure for holding parasites in check until the ani- mals can be dipped or sprayed. SPRAYING Common parasites on or in the skin can be eradicated by proper spraying, but the method commonly practiced is not economical. PARASITES AND PARASITIC DISEASES OF HORSES 49 It is difficult to wet the hair coat of an animal with a spray, and much of the liquid runs off and is wasted. Spraying is not effective unless all parts of the skin and hair are well soaked. An ordinary orchard-spraying outfit or a common hand pump equipped with hose and spray nozzle may be utilized for spraying animals. FUMIGATING Fumigation consists in exposing animals to the fumes of burning sulphur (sulphur dioxide) or some other gas. The animals to be fumigated are placed in a gas-tight chamber with the head project- ing through an opening and the nose and eyes protected from the gas. (Fig. 26.) This method is often recommended for treating animals for external parasites. Investigations conducted by the Bureau of Animal Industry have shown that the present known methods of fumigating animals are not suitable for general use. The minimum effective concentration of sulphur dioxide for mange apparently is about 4 per cent and for lice about 1 per cent. Under ordinary conditions the concentration or percentage of gas in the air can not be raised to more than about 1.5 or 2 per cent by burning sulphur:in the gas chamber unless special apparatus is installed. Sulphur dioxide compressed to a liquid and stored in steel cylinders is available on the market. By using the compressed gas any desired concentration in the chamber within certain limits may be obtained. In winter, when the temperature is too lew for dipping, fumigation is feasible if a large number of horses are to be treated and competent men are available to super- vise the work. This method apparently has no other distinct advan- tage over dipping. DIPPING Dipping is the most effective known method of applying treat- ment for common external parasites. Dipping plants are so ar- ranged that the animals are immersed in hquid deep enough to swim in, and the entire body surface is well soaked. For dipping horses the dip in the vat should be kept at a depth of 70 to 80 inches, or suflicient to immerse completely the tallest animal to be dipped. Horses will carry out and retain from 2 to 4 quarts of dip each, and the depth of the hquid in the vat will be lowered accord- ingly. The total estimated quantity of dip which the animals carry out plus that required to charge the vat should equal the total quan- tity required, provided none is lost by leakage or otherwise wasted. The capacity of the vat is usually obtained by multiplying, in terms of inches, the average length by the average width, then the product by the depth. This gives approximately the number of cubic inches of space to be filled with dip. Divide this by 231 (the number of cubic inches in a gallon), and the result will be the number of gallons of dip needed to charge the vat. (Fig. 33.) To obtain the average length, add the length at the bottom to the length at the dip line and divide by two. The average width is ob- tained in the same manner. The depth should be taken at the center of the vat and from the bottom to the dip line only, and not to the 50 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE ‘top. All measurements should be made only of the space to be filled with dip, and not above the dip line. The capacities of the various tanks are obtained by a like process. Before dipping, the contents of the vat should be well stirred in order that the dip may be of uniform strength and temperature throughout. The pens, chutes, vat, etc., should be examined for pro- jecting nails or any object that might puncture or wound the horses, as the dip may injure those having fresh wounds. In dipping wild range horses it is nec- essary to have a gate or bar in the chute to prevent the animals from piling up in the vat. Horses should be watered and fed from two to four hours before dipping, and if heated by driv- ing they should be allowed to cool off be- fore entering the vat. The head of each animal should be completely submerged for an instant at least once while in the vat. The head should not be held under, but quickly ducked with a dipping fork and released. Two duck- ings of the head are advisable, especially if the animals are affected with scabies. Care should be taken to see that the inner surface of the ear is well soaked. In dipping for lice it is not necessary to FIGURE 33.—Dipping vat being filled with liquid hold horses in the vat, but if they have scabies they should be held in the vat two or three minutes. After leaving the vat the animals should be held in the draining pens until all surplus dip has drained off their bodies. (Fig. 34.) Dipping should be finished for the day early enough to dry the ani- mals before sunset. Before approving a dip for use in official dipping one of the requirements of the Bureau of Animal Industry is that there shall be PARASITES AND PARASITIC DISEASES OF HORSES 51 a practical field test for such dip. Of the various classes of dips used on horses, three only are on the approved list—arsenicals, lime-sul- phur, and nicotine. Of these the two most commonly used are the lime-sulphur dip for f mange and the ar- senical dip for lice and ticks. ARSENICAL DIP Arsenical dip, when properly used, eradicates biting and sucking lice, but it is not an effective rem- edy for mange. Pre- _pared arsenical dips have been placed on the market, but those which are permitted by the Government for use in dipping cattle for southern fever ticks are suit- able for use in dip- ping horses, mules, and asses for lice. The instructions on the label of the con- tainer should be fol- lowed in diluting and using ready-prepar- ed dips. The arseni- cal dip is not usually warmed or heated in the vat. It should be remem- bered that arsenical dip is a poison, and precaution should be taken to prevent in- E Asis tenets 8 se : | jury to man or ani- GURE 34.—Exit eee Sep ee pens of horse- mal. When it is handled and used with proper care it is a safe and effective remedy. Care should be taken not to get the clothing wet with the dip, and the hands should be washed frequently to prevent possible absorption of arsenic. Freshly treated animals should be held in the draining pens or other suitable place until all surplus dip has drained off. (Figs. 34 and 35.) If allowed to drain where pools of dip collect from which the animals may drink, or if the pasture or feed becomes soiled with arsenical dip, losses are liable to occur. If homemade arsenical dip is preferred to the proprietary brands, see United States Department of Agriculture Farmers’ Bulletin 1057 for full instructions for making it. 52 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE LIME-SULPHUR DIP Proprietary brands of liquid lme-sulphur may be purchased, and many of them are equal to or even better than the homemade product. Manufacturers have also placed on the market a product commonly known as dry hme-sulphur, made by evaporating, in vacuo or in the presence of an inert gas, concentrated hme-sulphur solution to which a small amount of cane sugar has been added to act as a stabilizing agent. Dry hme-sulphur is readily soluble in hot water, and it is being extensively used as a dip for animals and as an insecticide for - plants. Prepared dips should be diluted and used in accordance with instructions printed on the label of the container. Lime-sul- phur dips are efficacious and dependable remedies for mange, but they are not effective against lice and ticks. Homemade lme-sulphur dip is made in the proportion of 12 pounds of unslaked lime (or 16 pounds of commercial hydrated FIGURE 35.—Superstructure and draining pen of cage vat lime) and 24 pounds of flowers of sulphur to 100 gallons of water. The lime and sulphur should be weighed and the water measured; do not trust to guess work. Slake the lime in a shallow, water-tight box or tank and add water enough to form a thin paste. Sift the sulphur into the paste and mix well with a broad hoe until a mixture of about the consistence of mortar is formed, adding water as re- quired. Put the mixture into 30 gallons of boiling water, adding it slowly so as not to interrupt the boiling, and boil until the sulphur disappears from the. surface. The boiling should be continued for from one and a half to two hours without cessation, and the mixture stirred to prevent settling and caking on the bottom. When the sul- phur has disappeared from the surface and the mixture is of a choco- late or dark-amber color, the boiling should be discontinued. The contents of the boiling tank should be drawn off or dipped out and placed in the settling tank and allowed to stand until all solids have settled to the bottom and the liquid is clear. An ordinary water- tight barrel will serve very well for a settling tank at a small vat. A PARASITES AND PARASITIC DISEASES OF HORSES 5S settling tank of any kind should have an outlet at least 4 inches from the bottom in order that the clear liquid may be drawn off without becoming mixed with any of the sediment. When the sediment has fully settled draw off the liquid into the dipping vat and add warm water to make a total of 100 gallons of dip. When mixed and cooked as specified above the concentrate is three and one-third times the strength required for the dip in the vat, so that to every 30 gallons of such concentrate 70 gallons of warm water should be added to make a dip of the required strength. In preparing lime-sulphur dip in large quantities several hun- dred gallons of concentrate are often made at one time in a single large cooking tank. The quantity made at one boiling is limited only by the facilities at hand. If the boiling tank is of sufficient capacity, a large enough quantity of dip should be cooked at one FicurE 36.—Cage vat in operation time to dip the herd. The quantity of mixture in the cooking tank may be varied at will, but the proportions of the various ingredients should not be altered. NICOTINE DIPS The nicotine dips sold under various trade names are commonly used for dipping animals and spraying plants for insect pests. They are efficacious remedies for horse lice and mange when diluted with water so that the solution contains not less than five one-hun- dredths of 1 per cent nicotine. If used much stronger, they are liable to injure horses, especially if the animals are dipped while they are warm from exercise or hot weather. Nicotine dips are generally used warm, but should not be heated above 110° F. The temperature of the bath should be maintained at 90° to 95°. Sulphur is sometimes added to nicotine dips in the proportion of 16 pounds of flowers of swphur to 100 gallons of 54. CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE diluted dip. The addition of sulphur increases the effectiveness of the dip for mange and extends the period of protection against reinfestation. These dips should be diluted and used in accordance with instructions printed on the label of the container. Do not use a nicotine dip the strength of which is not given on the label. COAL-TAR CRESOTE DIPS The coal-tar creosote dips, commonly known as coal-tar dips, are sold under many trade names. They are made from coal-tar derivatives, and the principal ingredient is creosote oil, which is made miscible with water by means of soap. When diluted with soft water they are efficacious in eradicating lice, but they are not dependable remedies for seacoae mange. Before using a coal-tar creosote dip in hard or alkeline: water, dilute a small, measured quantity of the dip with the water in the proportion to be used in dipping and place in a clean glass container. If, after standing for one hour, an oily layer or mass of globules appears either at the top or at the bottom of the hquid, ‘the dip should not be used with that kind of water, as it is liable to injure the animals. Injury may occur even when there is no apparent sepa- ration in the dip so tested. The coal-tar creosote dips may be used cold or warm, but the temperature of the bath should not exceed 95° F. They should be diluted and used in accordance with the instructions printed on the label of the container. OIL DIPS Kerosene, crude petroleum, crank-case drainings from gasoline motors, and other oils and greases are commonly used in treating horses for external parasites. When properly used they will control mange and lice, but they often injure horses by blistering the skin and causing the hair to fall out. Oil dips are not recommended for common. use in dipping horses. Cottonseed oil and kerosene, equal parts, or kerosene one-half pint to 1 pound of lard or crude petroleum is often apphed by hand to hold mange and lice in check when the weather is too cold for dipping. DIPPING VATS In those sections of the United States where there are a large number of horses to be dipped cattle-dipping vats usually are avail- able, and they can be utilized for dipping horses. (Fig. 33.) Plans of cattle- dipping vats suitable for dipping horses are given in Farmers’ Bulletins 1017 and 1057. The so-called cage vats are sometimes used for dipping horses. (Fig. 35.) In these vats the animal is placed in a movable cage and lowered into the bath by means of a windlass or other mechanical apparatus. (Fig. 36.) The operations are much slower than in the longitudinal vat. Portable, galvanized-metal vats may be purchased, and they are suitable for dipping a small number of animals. After digging a trench and setting the vat so that the top is flush with the surface of the ground, a Aide and slide board should be provided as a means of getting the horses into the vat. ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE WHEN THIS PUBLICATION WAS LAST PRINTED Directorof-hegqulatory Work.2 222-3 DirrectoTmopeclension Work. 22. 222 ee Director of Personnel and Business Adminis- tration. DP ECCLOTRO{MUNTORNUGLUON 522s 2 oo eS SLIDE SS 5 ES a ae Bureau of Agricultural Economics____--_ ~~ - Bureau of Agricultural Engineering______-- PUNCH OMPAUIIGILG I NAUSETY == = Bureau of Biological Survey_....-...--------- Bureau of; Chemistry and Soils--. 222.222 Office of Cooperative Extension Work_____--_- TSUTCOW Of WOT Industry <2 BUNPONO; EMULOMOLOGY > se ee Oficeo; Paperment staons= —. | Soe Food and Drug Administration_____------- Bureau of Home Economics__-__---------- LETS SS LS ee ee eae SECON OV LAL GML NO WSUGA = a BUCO Ope ion, GQ Uaraniine: 2. 2 === = Eiee Oe eliCeLOGds=— = NDT OG Pw EVAN OIE) See ee el a ae eee ARTHUR M. Hype. R. W. Dunuap. A. F. Woops. WaLtTER G. CAMPBELL. C. W. WARBURTON. W. W. STOCKBERGER. M.S. EISENHOWER. E. L. MARSHALL. Nits A. OLSEN, Chief. S. H. McCrory, Chief. JoHN R. Mower, Chief. Pauut G. RepineTON, Chief. H. G. Knieut, Chief. C. B. Smiru, Chief. O. E. ReeEp, Chief. C. L. Maruatt, Chief. JAMES T. JARDINE, Chief. WaLtreR G. CAMPBELL, Director of Regulatory Work, in Charge. Re Yo SruareT. Chef: Je We J Duvut,; Chief. LoutsE STANLEY, Chief. CLARIBEL R. BARNETT, Librarian. WiLiiamM A. Tay tor, Chief. Leg A. Srrone, Chief. Tuomas H. MacDona.tp, Chief. CHarues F. Marvin Chief. 59 U.S. GOVERNMENT PRINTING OFFICE: 1933 For sale by the Superintendent of Documents, Washington, D.C. - - - Price 5 cents me Ae ee a Ned + eal ft. ‘ ai ~ — < ms = Fad : : ia ; ey tee Me ee ages Sea SS ie F - ps 5 ; ey Se OS Perak : “3 een a a ; oe ene 2 : = Pe _ : - - 2 A in wa ge het ae = 4 . 2 ‘