Parasites and parasitic diseases of horses

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UNITED STATES DEPARTMENT OF AGRICULTURE
CIRCULAR No. 148

R en Va
Washington, D. C. Rev ede

Parasit
ana Parasitic
of Horses

By

Issued November 1930
Revised January 1933

Slightly revised January 1936 |
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BENJAMIN SCHWARTZ

Senior Zoologist

MARION IMES

Senior Veterinarian

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WILLARD H. WRIGHT

Associate Veterinarian
Zoological Division, Bureau of Animal Industry

For sale by the Superintendent of Documents, Washington, D.C.

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CIRCULAR No. 148

Issued November 1930; revised January 1933; slightly revised January 1936

UNITED STATES DEPARTMENT OF AGRICULTURE
WASHINGTON, D.C.

PARASITES AND PARASITIC DISEASES OF HORSES'

By BENJAMIN SCHWARTZ, Senior Zoologist, MARIon IMES, Senior Veterinarian,
‘ and WILLARD H. WricHT, Associate Veterinarian, Zoological Division, Bureau
of Animal Industry

CONTENTS
Page Page
Internal parasites of horses.....-....-.----_- 1 | Internal parasites of horses—Continued.
Abundance and location_____-_-_----_--__ 1 Misposaliof mantresas see sees esse ee 31
Symptoms and damage produced by Summary of control measures_____.______ 32
DATASET CSE se ete wi a ie is es Ba te 1 | External parasites of horses__________-______- 34
General control measures__________---__- 2 IFLOTSE ICO ws Met A Ne RIS Ey ie ee 34
Medicinal'treatmentie ase 522 oe eee 3 IFLOTVSe Manse se eee ee eee ete 38
IP ROCOZ OD eee ea Rats eee cesta 4 ARKO) 5) HERO aie Ot ean enema TE Tae 45
WOLD AaLasites es ase ee ane eee 5 Treating horses for external parasites__- 48
CO eR rr ys ie Or a et

INTERNAL PARASITES OF HORSES?
ABUNDANCE AND LOCATION

HE TERM PARASITE as used in this circular refers to forms
4 of animal life which, for the purpose of obtaining food and
shelter, live on or in the bodies of other animals which are larger
than the parasites and are known as hosts. All classes of domesti-
cated animals harbor numerous kinds of parasites, and horses, in
particular, are liable to infestation not only with many different
kinds but also with very large numbers of these pests. A horse’s
stomach may contain hundreds of bots, and the small intestine may
be packed with large roundworms. The large intestine of the horse
is a location especially preferred by parasites, and very often the
colon and cecum are found to be teeming with hundreds or thousands
of wriggling, parasitic worms, some free in the lumen and others
attached to the walls of the gut. Several kinds of worm parasites
present in the gut and elsewhere have previously wandered through
various parts of the horse’s body before reaching their final locations.
In fact, there is hardly an organ or a tissue in the horse which is
absolutely free from possible attacks by mature parasites or by their
wandering larval forms.

SYMPTOMS AND DAMAGE PRODUCED BY PARASITES

Parasitic diseases, unlike diseases caused by bacteria, are seldom
spectacular in their onset and symptoms and are marked by a slowly

1 This circular supersedes Farmers’ Bulletin No. 1493, Lice, Mange, and Ticks of Horses.
* By Benjamin Schwartz and Willard H. Wright. Many of the illustrations in this
section of the circular were drawn by Joseph E. Alicata, junior zoologist.

138442 °—37 a

4 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

progressing chain of symptoms which the owner may entirely over-
look or confuse with other conditions. The general symptoms of
worm infestation in the horse are unthriftiness, weakness, emacia-
tion, tucked-up flanks, distended abdomen, rough coat, whitening or
bleaching of the mucous membranes (noticed particularly in the
mucous lining of the eyelids and mouth), and in some cases frequent
eolics and diarrhea. The appetite usually remains good-and the ani-
mal shows no rise in temperature. Heavily parasitized animals tire
quickly and are frequently unable to stand heavy work.

Parasites are particularly damaging to young, growing animals.
They attack the foal when it should be making its best growth and
produce stunting and lack of development. A considerable part of
this damage is a result, no doubt, of the wanderings of the larval
worms through various parts of the body of the host before they
reach their preferred location where they develop to maturity.

While the death rate from parasitic infestation is not high, never-
theless these internal pests cause considerable damage. The loss is
represented largely by the poor development and stunting of foals,
inability of heavily parasitized horses to do a normal amount of
work, added costs of feed and maintenance, and loss of working time
from verminous colics. The aggregate loss resulting from these con-
citions is sufficient to warrant the attention of horse owners to the
subject of parasite control.

GENERAL CONTROL MEASURES

Most parasites of livestock owe their perpetuation to the fact that
domestic animals often take their food from the same places they
deposit their fecal matter. The eggs of parasites are passed by
horses with the manure in stables and on pastures and then go
through various stages of development, after which either the eggs
or the larval worms reach the interior of the horse with the food and
drinking water. Prevention must be directed toward breaking this
cycle. Stables and paddocks should be kept in a sanitary condition
by the frequent removal of manure. Concrete standings, although
objected to by some horsemen, have the advantage of being easily
cleaned and provide a relatively unfavorable medium for the de-
velopment of parasites. If wooden standings are used, the timber
should be sound. Rotten, moisture-soaked floors are difficult to keep
clean, and they provide a favorable medium for the development
of parasites. If standings of earth are used, it is advisable to re-
move the top layer of soil down to 10 or 12 inches once or twice a
year and replace it with clean, uncontaminated soil.

Horses should be fed grain from feed boxes and hay from racks
which are sufficiently high above the ground or the floor of the stall
to prevent contamination of the feed with manure. Watering
troughs should be so constructed as to prevent similar contamination
of the drinking water. Horses should not be forced to obtain drink-
ing water from pasture or barnyard pools. In general, low, wet
pastures are more favorable for the propagation of parasites than
are high, well-drained areas. Animals grazed on heavily stocked,
permanent pastures have greater opportunity for picking up para-
site eggs and larve than those changed frequently from one pasture
to another. For this reason pastures should be changed as often as

@

PARASITES AND PARASITIC DISEASES OF HORSES 3

possible. The common practice of spreading horse manure on pas-
ture plots adds to the parasite burden of the pastures. Suitable
treatment of manure before spreading, as described in this circular, |
will prevent this added contamination.

MEDICINAL TREATMENT

It is not always practicable on the average farm to apply the
sanitary measures necessary for the prevention of parasitic infesta-
tion in horses. Treatment is, therefore, an important consideration.
Periodic treatment will not only reduce infestation in parasitized
horses and render the animals more serviceable but will likewise
reduce the output of eggs in the manure, with a resultant decrease
in stable and pasture contamination.

Prevention of parasites in horses by the application of sanitary
measures is the business of the horse owner, but the diagnosis and
treatment of parasitic diseases are functions of the veterinarian.
Different parasites require different and more or less specific treat-
ments. Before these treatments can be intelligently applied it is
necessary to know which species of parasites are present. The veteri-
narian is qualified by training and experience to ascertain this.

Drugs used in treatments for horse parasites should be adminis-
tered, as a rule, in capsules or by stomach tube, the latter being the
preferred method for certain drugs. If capsules containing an irri-
tant or volatile drug are broken in the mouth, some of the drug may
be drawn into the windpipe and cause serious consequences. All
drugs used in the treatment of horse parasites are poisonous, being
intended to poison the parasites, and great care must be used in
selecting the dose in accordance with the weight and condition of the
animal. Some drugs should not be used in the presence of certain
conditions and, if used under such unfavorable circumstances, may
cause serious results. Because treatment involves diagnosis and an
intimate knowledge of how a drug acts and when to use it or not
to use it, it 1s advisable that all treatments for horse parasites be
administered by a veterinarian.

The treatments recommended in this circular are, for the most
part, those which have been found by experimentation to be the
most effective for the parasite or parasites involved. Many drugs,
some of them long purported to .be of value for the expulsion of
worms from the horse, have been found to be practically worthless
for this purpose when critically tested. Among such preparations
may be mentioned iron sulphate, arsenic, copper sulphate, and tartar
emetic. These drugs are frequently prescribed for adminstration in
the feed, a method which is very unsatisfactory and ineffective even
with drugs known to be effective when given in capsule or by stom-
ach tube. For this reason it is essential to administer worm reme-
dies in accordance with the methods recommended in this circular.

Before the administration of worm remedies animals should be
fasted for the length of time prescribed under the various treat-
ments. The withholding of feed reduces the bulk of the contents
of the digestive tract and permits the drug to reach the parasites
more certainly and effectively. Water should be allowed during
the period of preliminary fasting, but it is advisable to withhold
both feed and water for four or five hours after dosing. To keep

4 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

parasitic infestation at a minimum and avoid losses from this source,
it is advisable to adopt a program of regular treatment. The usual
procedure is to administer treatments twice a year. In the northern
part of the United States, animals may be treated for worm parasites
in the late spring or early summer and in the fall. In the South,
owing to the shorter and milder winter and the more abundant
warmth and moisture, it may be necessary to treat oftener. Judg-
ment, based on experience, is a better basis for procedure than any
general rule. Treatment for the removal of bots may be adminis-
tered 30 days after the first freezing weather lasting 24 hours or
longer.

Tpternel parasites occur in various locations in the body of the
host animal, such as the alimentary canal, lungs, liver, kidneys,
blood, and various organs and tissues other than the skin. They
include various forms of animal life known as Protozoa, worms, the
larval forms of certain insects, and some forms closely related to
insects. The various kinds are discussed in detail in the following
pages:

PROTOZOA

Protozoa are relatively low forms of animal life, microscopic in
size, and consisting of but a single cell. The parasitic Protozoa of
domesticated animals are known to occur in various locations, and
are especially common in the alimentary canal and in the blood.
Fortunately, horses in the United States are relatively free from
certain disease-producing protozoan parasites which occur in horses
in other parts of the world where they constitute a limiting factor
in horse production. The only known pathogenic protozoan para-
site of horses in this country is the organism, one of the trypano-
somes, which produces dourine.* Trypanosomes closely related to
this organism occur in the blood of horses in South America, Asia,
the Philippine Islands, and elsewhere and produce serious and fatal
diseases. Up to the present time these parasites have not become
established in this country, and quarantine measures to keep them
out are enforced.

Protozoan parasites of various kinds often occur in large num-
bers in the cecum and the upper colon of horses, but these forms
are not definitely known to produce any digestive or other disturb-
ances and are usually regarded as comparatively harmless.

WORM PARASITES

The worm parasites of horses include flukes, tapeworms, and
roundworms, the last-mentioned group being the most common and
the most injurious.

FLUKES

Flukes or trematodes are soft, more or less flattened, leaf-shaped
worms, occurring in various locations, especially in the digestive
tract and in organs which communicate with the digestive tract.
Only a few kinds of flukes are known to occur in horses, and several

3Information concerning dourine is published in Farmers’ Bulletin 1146, Dourine of
Horses. ;

PARASITES AND PARASITIC DISEASES OF HORSES 5

of the forms which have been reported from these animals normally
occur in other hosts and are only accidental parasites of the horse.
The only fluke likely to be encountered in horses in this country is
the common liver fluke of cattle and sheep, which is occasionally
found in the horse. Horses on the west coast, in the South, and in
the Southwest are likely to become infested with liver flukes, espe-
cially if they have access to pastures on which fluky sheep and cattle
have grazed. Liver flukes occur in the bile ducts of the liver and
produce a serious disease, especially in sheep. ‘The larval forms of
these worms require snails as intermediate hosts and can maintain
themselves only on pastures sufficiently wet to favor the occurrence
of certain kinds of snails.

Liver-fluke disease in horses has not been extensively studied,
because it is relatively rare in these animals. Prevention consists in
keeping horses off low and swampy pastures, and these precautions
should be especially observed in those parts of the United States where
liver flukes are known to occur. Such pastures favor parasites in
general. Farmers’ Bulletin 1330 gives information on fluke control.

Treatment.—There is no established treatment for liver-fluke in-
festation in the horse. However, carbon tetrachloride in small doses
has a specific action on the common liver fluke of sheep and is widely
used as a treatment for fluke infestation in these animals. Carbon
tetrachloride may be given with safety to adult horses in doses of
from 6 to 12 fluid drams (25 to 50 cubic centimeters) and in these
doses should be effective for the destruction of the flukes.

TAPEWORMS

A tapeworm is an elongated flattened worm consisting of a head
and a chain of segments. Each mature segment contains both male
and female organs. The head of a horse tapeworm is provided with
four suckers by means of which the parasite attaches itself to the
wall of the gut. The segments of these tapeworms are considerably
wider than long and those which are farthest from the head are the
ones which contain eggs. The ripe or gravid segments which con-
tain the eggs become detached from the rest of the chain and are
expelled from the body with the droppings. Beyond this point
nothing is known as regards the further development of horse
tapeworms.

Horses are known to harbor three species of tapeworms, as follows:

The large horse tapeworm, Anoplocephala magna (fig. 1), usually
is from 31% to 10 inches long. The head is about two-fifths of an
inch in width and bears four prominent suckers. With the excep-
tion of those immediately adjoining the head, the segments are con-
siderably wider than the head. This parasite occurs in the small
intestine and occasionally also in the stomach.

The dwarf tapeworm of horses, Anoplocephala mamillana (fig. 2),
is only from about one-fourth of an inch to 2 inches long and from
one-sixth to one-fourth of an inch wide; the head of this worm is
very minute and is barely visible to the naked eye. This tapeworm
occurs in the small intestine and is occasionally found in the stomach.

A third species of tapeworm, intermediate in size between the
large tapeworm and the dwarf tapeworm, is known as the perfoliate
tapeworm, Anoplocephala perfoliata. It is usually from about

6 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

three-fifths of an inch to over 3 inches long. It occurs usually in
the cecum and is also found in the lower portion, rarely in the
upper portion, of the small intestine. This species is apparently
much less common in American horses than the other two species
of tapeworms.

Symptoms and lesions——In light infestations no symptoms are
present. Horses which are heavily infested with tapeworms may

FIGURE 1.—AlImost a gallon of large tapeworms, Anoplocephala magna, removed post-
mortem from a horse. About one-half natural size. (Photograph by courtesy of
the Agricultural and Mechanical College of Texas)

suffer from intestinal catarrh, show digestive disturbances of vari-
ous sorts, and in cases of very severe infestations they may become
emaciated and anemic. The perfoliate tapeworm of the horse
often occurs in large numbers when present at all, and is said to
produce inflammation of the intestines; sometimes it ruptures the
wall of the cecum. The attachment of tapeworms of this species
to the wall of the cecum produces small ulcers

in the regions to which the worms are attached.
Treatment.—Very little is known regarding
treatment for tapeworms in the horse. The fol-
Ficurp £—The dwarf lowing treatments have been recommended but
EO nitine <= ~have not had critical test to determine their pre-

phala mamillana, of :
the horse. Natural cjse value.

i Oil of turpentine is said to be an effective
remedy. This is given in a dose of 2 fluid ounces (60 cubic centi-
meters) in capsules, followed every second day by 1 ounce (30 cubic
centimeters) in capsule until five or six doses have been given. The
last dose is immediately preceded or followed by 1 quart of raw
linseed oil. It would seem that the drugs used for the treatment of
tapeworm infestation in other animals would offer more promise.

a

PARASITES AND PARASITIC DISEASES OF HORSES i.

Areca nut may be of value for the removal of tapeworms from
the horse. Areca nut, freshly ground, may be given to adult horses
in doses of from 1 to 1.5 ounces (30 to 45 grams) in capsules after
fasting the animals for 24 to 36 hours. The drug has a purgative
action, but if the bowels do not move within four or five hours, it is
advisable to administer 1 to 2 pints of raw linseed oil. Areca nut
should not be given to very old or very young animals or to those in
a weakened condition.

Kamala may be found to be of value for the removal of horse
tapeworms. Kamala may be given to adult horses in doses of 1
ounce (30 grams) in capsule, after they are fasted from 24 to 36
hours. The drug itself has a purgative action and seldom needs to
be followed by a purgative. Kamala should not be given to very
young or very old animals, to those in a weakened condition, or to
those suffering from febrile diseases, such as influenza, distemper’
(strangles), and infectious anemia (Swamp fever).

Oleoresin of male fern is another drug which may be of value
for the expulsion of tapeworms from the horse. This drug may be

iven to adult horses in doses of 3 to 6 drams (10 to 20 grams) in
capsules after fasting the animal for 24 hours. The drug should be
immediately preceded or followed by 1 quart of raw lnseed oil.

The foregoing drugs should be used with caution and given only
to animals in good condition and presumably able to withstand any
poisonous effects of the drugs.

Prevention—In the absence of information concerning the life
histories of horse tapeworms no definite control measures can be
recommended. It should be remembered in this connection that
the eggs present in gravid segments which are eliminated with the
manure are the starting points of new infestations. Any measures
which are taken with reference to the proper disposal of manure
will aid in preventing infestation with these parasites, especially if
the manure is stored and permitted to undergo self sterilization by
heating, so far as the destruction of parasite eggs and larve is con-
cerned. ‘This procedure is described later in this circular.

ROUNDWORMS

Roundworms or threadworms comprise the vast majority of para-
sites which infest horses. These worms, which are also known as
nematodes, are elongated, cylindrical in shape, and usually tapering
at both ends. Some roundworms are almost white, some are grayish
white, most of them are yellowish in color, and some are pinkish or
blood red. Roundworms occurring in the horse have a considerable
range of size, the large, intestinal roundworm or ascarid being from
6 inches to over a foot long, while the small stomach worm is only
about one-fifth of an inch long. Roundworms reproduce by means
of eggs which are produced by the female worms. The eggs are
usually eliminated from the horse’s body with the manure. Some
species of roundworms must be taken up by an intermediate host in
which they undergo part of their development, while other species
are transmitted from one animal to another directly by eggs or by
larvee which have emerged from eggs. Most roundworms which oc-
cur in the horse are transmitted directly by eggs and larve, with-
out the use of an intermediate host.

8 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

ROUNDWORMS IN THE STOMACH

Two kinds of worms are present in the stomach of horses. One
kind, designated here as the large stomach worms, is represented by
three distinct species in the horse; these parasites are transmitted by
flies. The other kind, designated as the small stomach worm of the
horse, is represented by only one species. The small stomach worm
is acquired by horses directly as the result of swallowing infective
larvee which occur on pastures. The larve may also be taken in by
horses with water and with dry feed.

THE LARGE STOMACH WORMS

The large stomach worms (fig. 3) are relatively long and slen-
der, are whitish in color, and occur either free in the stomach, em-
bedded in mucus, attached to the wall of the stomach, or in tumors

7 of the stomach wall, for which
tumors these worms are respon-
sible.

One species, Carter’s stomach
worm, Habronema muscae, of the

- * inch to nearly an inch long.
This parasite occurs free in the

horse, is from about one-third
stomach or attached to the wall
of the stomach. A second spe-
cies, the small-mouthed stomach
worm, //. majus, synonym /.

microstoma, 1s similar in size
and appearance to the above
species. While this form may
A occur free in the stomach, it is

capable of penetrating its wall

FIGURE 8.—Large stomach worms of the and causing sores. A third spe-

Perse. cai er onema_microsioma;y others Gees athe) lar ce-mouumeG scuonna tim

worm, H. megastoma, of the

horse is the smallest of the three species, ranging in length from less

than one-third of an inch to about one-half inch. These worms

occur in tumors found in the wall of the stomach; the tumors may

become very large, attaining the size of a fist or even of a child’s
head. Usually, however, they are much smaller.

Life history.—(Fig. 4.) The eggs of horse stomach worms have
very flexible shells; they are deposited in the lumen of the stomach
and are eliminated from the horse’s body with the feces. When
the eggs are swallowed by maggots of house flies, stable flies, or
other flies which breed in horse manure, further development takes
place which keeps pace with the development of the maggots. The
larve of Carter’s stomach worm of the horse develop for the most
part in house flies while those of the small-mouthed stomach worms
of the horse have stable flies as their usual intermediate hosts, though
they are known to develop also in house flies and other flies. The
larvee of the large-mouthed stomach worms of the horse develop in
various species of nonbiting flies, including house flies. These larvee
attain their full growth in the flies when the latter emerge from the

PARASITES AND PARASITIC DISEASES OF HORSES 9

pup. Horses may become infested with stomach worms as a
result of swallowing live, infected flies or infected flies which have
been dead a short time and still contain the live larval worms.
Another and probably more common way in which horses become
infected with these parasites is as follows: As the flies suck the
moisture of the lips and nose, the larvee, which are present in the
mouth parts of the insects, escape, the heat and moisture of the
horse’s body stimulating the larve to wriggle out of the flies. Once

TE €995 COMIMaMIIG YOUNG,
worms are expel/ed
Yrom the digestive / (a)
track wit
SIQHUPE.

The 17a@+tlre
Worms 17 The Storiath

lap 17101 EGGS.

lhe eggs are swallowed by fly

WHNAG907S (a) he young worms avelop

Wt the rnaggor and tr the pupa tb) and
are infective wher the adiu/7

Sly (€) ernerges.

Horses become tifested as /
aresul? of swallowia ph ae
“pected files or Be Cy i)
Sorvae which escape ~te
Jrom flies while
the latter are feeding
on the mosture of the lips:

4

Ficurn 4.—Life cycle of one of the large stomach worms, Habronema muscae, of the
‘horse. The illustrations of the adult worms are enlarged about 2 times; those of
the eggs are enlarged about 150 times.

the larve are on the lips they are readily swallowed. Those larve
which get into the nasal’ cavities probably wriggle into the pharynx
and are also swallowed. When the larve reach the stomach they
are in their normal location where they settle down and develop to
maturity. It is possible that the small-mouthed stomach worm is
transmitted by the bite of the stable fly.

Symptoms and lesions —No definite symptoms which indicate the
presence of these parasites in the stomach are known. The worms
are injurious because of their tendency to attach themselves to and to
penetrate into the stomach wall and, in the case of the large-mouthed

13423 (———e

10 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

stomach worm, because of the tumors which they produce. The
tumors interfere to a considerable extent with the proper functioning
of the stomach. When large tumors are situated near the junction
of the stomach and intestine they interfere mechanically with the
passage of food. The most evident injury occasioned by the large
stomach worms is produced by the larve which get into the skin of
horses where they are commonly associated with a skin disease known
as Summer sores.

Treatment.—A high degree of efficacy for the destruction of Z.
muscae and H. microstoma has been obtained by the use of the fol-
lowing method of treatment. The animal should be fasted for from
18 to 24 hours and the stomach washed out by injecting through a
stomach tube 8 to 10 quarts of a 2 per cent solution of sodium bicar-
bonate (baking soda) heated to 105° F. The solution tends to remove
the thick layer of tenacious mucus which normally covers the lining
of the stomach and renders the stomach worms more accessible
to the action of drugs. It is advisable, though not necessary, to
siphon off the sodium bicarbonate solution. If the solution is not
siphoned off, an interval of 15 to 20 minutes should elapse before
further treatment. Carbon disulphide should then be administered
in capsule or by stomach tube in a dose of 6 fluid drams (24 cubic
centimeters) for a 1,000-pound animal, or at a dose rate of 1.5 fluid
drams (6 cubic centimeters) for each 250 pounds of weight. No
purgative should be used with this treatment. H. megastoma in
stomach tumors is not affected by this treatment and is inaccessible
to any method of treatment known at present.

Prevention.—Prevention of stomach-worm infestation in horses
involves the storage of manure in closed containers, in order to de-
crease the number of flies which breed in manure, or the application
of other control measures designed to prevent flies from breeding.
The use of containers for storing manure with a view to destroying
egos and larve of parasites is discussed subsequently in this circular.
The United States Bureau of Entomology has devised a trap de-
signed to destroy fly maggots which breed in manure. ‘The trap is
based on the observation that maggots, when fully grown, migrate
out of moist manure and if they are permitted to escape through
spaces between the boards of an open manure platform raised on
posts and set in a concrete basin of water, they are caught in the
basin and drowned. This and various other methods of controlling
the house fly and stable fly are given in Farmers’ Bulletins Nos. 1408
and 1097.

SUMMER SORES

A skin disease of horses, known as summer sores and characterized
by pronounced skin lesions, is associated in some parts of the world,
including the United States, with the larve of the large stomach
worms of horses. The sores may be as small as a millet seed, but
are usually about the size of a pea and may attain a size about an
inch in diameter. The sores are covered by a soft, brownish-red,
pulpy material with cracks or furrows which are filled with pus.
In the midst of the softened mass there are small, rounded granu-
lations which are firm in texture,

PARASITES AND PARASITIC DISEASES OF HORSES 11

This disease has been studied in Europe, Africa, and elsewhere,
where it has been noted that its seasonal occurrence corresponds to
the prevalence of flies. It is unlikely that the worm larve invade
the unbroken skin, but it appears to be well established that when a
horse’s skin is broken by some injury and when flies which carry
the worm larve feed on the sores, the larvae escape from the mouth
parts of the fly and live for a time in the wounds. These larvee irri-
tate the sore, so that instead of healing as a simple sore it may
become a more or less chronic thing which does not heal until after
the occurrence of frost in the fall.

Although conditions known as “summer sores” in horses are
known to occur in the United States, the disease has not been exten-
sively studied here and the relation of stomach-worm larve to sum-
mer sores still needs further investigation in this country. Recently
the occurrence of the larval worms from summer sores in horses in
the United States has been definitely reported.

Treatment for summer sores.—An astringent powder which is said
to prevent the extension of the trouble and to aid in healing consists
of the following: Plaster of Paris, 100 parts; alum, 20 parts; naph-
thalene, 10 parts; and quinine, 10 parts.

Good results are reported from the use of a caustic paste composed
of arsenious oxide, 1 part, and flour, 5 parts. Washing the sores with
ether or chloroform and then painting them with collodion has also
been recommended. Some veterinarians prefer the use of a 5 to 10
per cent solution of formalin, applied by means of a cotton pad
which is left on the sores for two to three hours every day.

Prevention.—Skin injuries should be protected from flies by the
use of pine-tar oil or other means to prevent their conversion into
summer sores.

THE SMALL STOMACH WORM

This parasite, 77ichostrongylus awxei, occurs in the lining of the
stomach, and is likely to be overlooked as the worms are very slender
and only about one-fifth of an inch or less in length.

Life history.—The life history of this parasite has not been defi-
nitely ascertained. In a general way its life history is similar to
that of blood strongyles, described elsewhere in this circular, with
respect to the development of the eggs and larve on pastures. It is
also fairly certain that infestation is direct, and results from the
swallowing, by horses, of the infective larve with food or water.
However, these worms burrow only into the stomach wall and are
not known to wander extensively, as young worms, throughout. the
body of the horse.

Symptoms and lesions——These parasites injure the stomach wall.
Sometimes the stomach lining shows areas superficially like a ring-
worm or a mass of small tumors. (Fig. 5.) In addition to these
injuries, the parasites contribute to general gross parasitism in
horses which is characterized by weakness, paleness of the mucous
surfaces, wasting, and digestive disturbances.

Treatment.—Treatment for the removal of this parasite is similar
to that recommended for the large stomach worms. However, this
treatment has not had critical test to determine its exact. efficacy
against the small stomach worm.

1,2. CIRCULAR 148, U. 8. DEPARTMENT OF AGRICULTURE

Prevention.—Preventive measures are similar in a general way to
those discussed in connection with preventive measures against blood-
worms and other strongyles. The similarity in control measures is
based on similar life histories.

THE LARGE INTESTINAL ROUNDWORMS OR ASCARIDS

The large intestinal roundworms, Ascaris equorum, of horses (Fig.
6), also known as ascarids, are cylindrical in shape, yellowish white
in appearance, and from about the size of an ordinary lead pencil to
about a foot long when fully grown. The head is clearly marked
off from the rest of the body and bears three clearly distinguishable
lips. Closely related worms occur in pigs, cattle, and human beings.
Ascarids occasionally pass out of the bowels spontaneously, in which

FicurE 5.—Portion of the inner lining of a horse’s_ stomach, showing lesions
produced by the small stomach worm, Trichostrongylus azei. (Photograph by
courtesy of the Agricultural and Mechanical College of Texas)

case they are readily seen, and in horses this is said to take place in
the spring of the year.

These worms are located in the upper part, less often in the middle
and lower parts, of the small intestine; they are occasionally found
in the cecum and in the stomach. They may occur in large num-
bers, especially in foals and in young horses.

Life history—(Fig. 7.) The female worms produce large num-
bers of eggs which are microscopic in size. The eggs are deposited
in the lumen of the horse’s intestines and are expelled from the
bowels in the manure. Under favorable conditions of temperature
and with an adequate supply of moisture, the eggs develop on the
ground and on pastures until they reach the infective stage, but the
embryos remain in their eggshells until they reach the gut of a sus-
ceptible horse. The thick eggshell protects the embryo it contains
against various unfavorable influences.

i

PARASITES AND PARASITIC DISEASES OF HORSES 13

During the summer months the eggs develop to the infective stage
in about two weeks. The low temperatures of cold weather retard
the development of the eggs, as does also lack of moisture. Ordinarily

sufficient moisture is present in horse ma-
nure to favor the development of the eggs.
Balls of manure which appear dry on the
surface commonly contain sufficient mois-
ture in the middle to permit the normal
development of these eggs. Excessive
drying destroys the vitality of ascarid
eggs,

If infective ascarid eggs are swallowed
by horses with grass, water, or dry feed
which has become contaminated with horse
manure, the embryos are liberated from
their shells in the horse’s intestine and
then burrow into the wall of the gut and
migrate with the blood stream to the liver.
From this organ they proceed in the blood
stream through the heart to the lungs. If
many worms go through the lungs at the
same time they injure this organ and may
produce pneumonia. This roundabout
journey from the intestine to the liver and
thence to the lungs is completed in
about a week. From the lungs the larve
crawl up the windpipe until they reach
the back of the mouth and are then swal-
lowed. On getting into the small intestine
from the stomach for the second time, they
settle down and develop to maturity in
from about two to two and a half months.
(Fig. 8.)

Symptoms and lesions—When ascarids
are present in large numbers, which is
likely to be the case in foals and young
horses, they produce digestive disturb-
ances of various sorts and may cause colic.
These parasites frequently become entan-
gled with one another, resulting in large
masses of worms which may plug the
lumen of the intestine. In an extreme con-
dition of this sort the results may be fatal.
Such an entangled mass of worms may
even rupture the wall of the intestine as
a result of continuous pressure on it.
These worms have also been reported as
being capable of perforating the wall of
the intestine, presumably as a result of

continually pushing their heads against it.

Ficure 6.—The large roundworm,
Ascaris equorum: A, male;
B, female. About one-half
natural size

In either case, a rupture

of the intestinal wall would usually cause the death of the horse.

In experimental infestations of horses

with ascarids, fever and

a cough have been observed during the early stages when the

14 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

worms were present in the lungs and in the windpipe and its
branches. It is probable that similar symptoms are present in heavy
ascarid infestations which are acquired naturally in stables and on
pastures. Ordinarily, ascarid infestations in foals result in un-
thrifty animals with rough, staring coats, and the removal of the
worms frequently leads to marked improvement in condition, hair
coat, and gain in weight.

Thus it is evident that the ascarid, both as an adult and as a
wandering larva, has the capacity for causing great damage, and
that its presence in horses, especially foals, is a possible source of

2
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CONANHONS ThE EUGS EAC?
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1WO WEEKS.

>” The rya@7vure HOTS
i the itestiies lay
PROUSQIIOS SS COGS:

Horses becore iifested
as a restl? of swallusing
Wifective eggs wills

Jood or ware

Ficurn 7.—Life cycle of the horse ascarid, Ascaris equorum. The eggs shown in
this illustration are enlarged about 50 times

danger. Heavy infestations, in which hundreds of worms may be
present, may cause illness and even death as a result of the horse’s
absorption of toxic products produced by the worms.
Treatment.—Carbon disulphide is an effective remedy for the re-
moval of ascarids from the horse. The drug is given as follows:
Fast the animal for 18 hours and give carbon disulphide in a dose
of 6 fluid drams (24 cubic centimeters) for a 1,000-pound animal or
at a dose rate of 1.5 fluid drams (6 cubic centimeters) for each 250
pounds of weight. The worms usually pass for several days follow-
ing treatment. Purgatives should not be given with this treat-

‘15
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f inflammation in the

PARASITES AND PARASITIC DISEASES OF HORSES
of the carbon disulphide.

Fats and oils should be avoided as they promote the absorp-

disulphide usually produces a limited area o

tion and increase the toxicity

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The animal should

Experimental investigations indicate that carbon tetrachloride is

also very effective for the removal of ascarids.
be fasted 18 hours and the carbon tetrachloride given in doses of

stomach of the horse. This inflammation is without serious consequen-
ces, however, and usually disappears in the course of a week or two.

16. CIRCULAR 148, U. 8. DEPARTMENT OF AGRICULTURE

from 6 to 12 fluid drams (25 to 50 cc) for a 1,000-pound animal.
This drug usually need not be accompanied with a purgative, but
it is advisable to give a saline purgative immediately following the
administration of carbon tetrachloride for the removal of worms,
particularly ascarids, from colts.

Prevention.—Prevention of ascarid infestation requires special
care of foals and young horses. The time to begin is before the foal
is born. The foaling barn should be of sanitary construction and
should be cleaned and washed with hot water and lye before the
pregnant mare is placed in it. The mare and foal should be kept
in a clean paddock adjoining the barn. It is best to use a paddock
from which other horses have been absent for at least a year. The
stable and paddock
in which the mare
and foal are kept
should be cleaned
daily if possible, lit-
ter and manure be-
ing removed.

These precautions
are designed to pre-
vent the foals from
becoming heavily
infested with asca-
rids at an early age,
and beforethey have
developed the neces-
sary reserve vitality
to cope successfully
with a heavy worm
infestation. When
the foal is moved to
a. pasture it 1s essen-
tial to select one
which is clean and
that has not been
used by horses for a
year or oncer
Horses may be
FIGURE ripe al es Leek Sea Note accumu- moved to cow and

sheep pastures and
vice versa, because parasites of ruminants are not transmissible to
horses, and equine parasites are not transmissible to cattle and
sheep, as a rule. Proper disposal of manure and sanitary meas-
ures recommended in connection with the control of blood strongyles
will also help to prevent infestation with ascarids.

While infestations with ascarids can be acquired on pastures,
and often are so acquired, it is important to remember that ill-kept
stables, in which manure is allowed to accumulate (fig. 9), are also
the sources of heavy infestations with intestinal roundworms, pin-
worms, and other threadworms. Under pasture conditions many
eggs and larve succumb to drought and to other unfavorable in-
fluences which prevail in the open. In manure-laden stalls parasite

¢

PARASITES AND PARASITIC DISEASES OF HORSES LW.

eggs and larve are largely protected from unfavorable influences and
they have an abundant supply of moisture and shade and a favorable
temperature for development. It is, therefore, important to pay
strict attention to stable sanitation and to remove manure frequently,
supply fresh bedding, clean water from sanitary watering troughs
(fig. 10), and dry feed in feed boxes and racks well raised above the
floor in order to prevent contamination with horse manure and con-
sequent gross infestation with these parasites. (Fig. 11.)

STRONGYLOIDES

Foals are commonly infested with very small and slender thread-
worms, Strongyloides westert, which occur in the small intestine.
These parasites, all of which are females, are whitish in color, about

FIGURE 10.—Type of sanitary watering trough

one-third of an inch long, and less than one two-hundred-and-
fiftieths of an inch wide.

These threadworms produce numerous eggs, microscopic in size.
and deposit them in the intestine of the infested foal from which
they are eliminated in the manure. The eggs develop very rapidly
on the ground and on pastures, and the larvee which emerge from
them may either transform directly into infective larve which serve
to infest other foals, or may develop into free-living males and fe-
males. As a rule both types of development take place, some larve
becoming infective while others develop into free-living adults. The
latter mate on the ground or in manure and the females produce eggs
and deposit them on soil or in manure. In a short time, under
favorable conditions, larvee emerge from these eggs. These larve
become infective and are capable of infecting horses.

UPS By 8

18 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

These parasites multiply very rapidly, the entire development on
the ground taking place in a few days. The infective larvee, whether
they hatched from the eggs eliminated with the feces or from the
eggs produced by the free-living generation of worms, are taken in
by horses with food and are also capable of penetrating the intact
skin. Within about two weeks after the larve have been taken up
by horses they have developed into mature females which soon begin
to discharge eggs into the intestine of the host.

Symptoms and lesions—While no definite symptoms have been
described in horses as resulting from infestation with these parasites,

) the worms are prob-
ably responsible for
diarrhea in foals,
These worms make
their appearance in
foals earlier than do
other parasites, and
the infestation tends
to become heavy as a
result. of reinfesta-
tions which may take
place rapidly and
often, because of the
brief period required
for development out-
side of the host. The
parasites are usually
embedded in the lin-
ing of the intestine
and doubtless produce
considerable irrita-
tion. The fact that
the infective Jarve
are capable of pene-
trating the skin adds
another complication
and it is probable that
foals acquire part of
their infestation while
lying down on _ pas-

Rs ie i, cate RUC Hi inaan Sent tures and in_ their
IGURE -—1type or Sanitary box stall. INOUE) Lee ox
and hayrack raised above the ground stalls. As the larve

penetrate the skin it
becomes reddened and obscure skin troubles in horses may be caused
by the penetration of these worms. The larval worms may carry
pathogenic bacteria into and through the skin.

Treatment.—N othing is known concerning effective treatment for
these threadworms. In severe cases of diarrhea, in foals, caused by
this parasite, carbon tetrachloride is worthy of trial. The drug may
be used for foals at a dose rate of 0.1 cubic centimeter per kilogram
(2.2 pounds) of body weight or 10 cubic centimeters (2.5 fluid drams)
for a 220-pound animal. In order to remove the bulk of ingesta in
the small intestine and render the parasites more accessible to treat-
ment, it is advisable to administer a purgative 24 hours before treat-

9

PARASITES AND PARASITIC DISEASES OF HORSES 19

ment, and to withhold feed until after the carbon tetrachloride has
been given. A suitable purgative for foals consists of castor oil, 4 to
§ ounces, and neutral oil (mineral oil) 1 pint. This treatment has
not had critical test to determine its precise value.

Prevention.—Prevention consists in special precautions with ref-
erence to stable sanitation, special care of foals, especially as regards
clean bedding which should be changed daily, if possible. Other
preventive measures are similar to those recommended in connection
with the discussion of ascarids and blood strongyles.

THE LARGE STRONGYLES OR PALISADE WORMS

The large strongyles are roundworms commonly known as blood
worms, red worms, sclerostomes, or palisade worms. ‘They are red in

Figure 12.—Portion of the tip of the cecum of a horse, showing blood strongyles
attached to the inner lining of the gut. The large worms are 8. equinus; the smail
ones are S. vulgaris. Natural size

color and are commonly found firmly attached to the wall of the gut
(fig. 12) by means of a rather formidable mouth cup. Three species
of blood strongyles are of common occurrence in the colon and cecum
of horses, as follows:

The large strongyle, Strongylus equinus (fig. 138, C), is from
about 11, ‘to nearly 2 inches long by about one twenty-fifth to one-
twelfth of an inch wide; the mouth cup contains three teeth. The
toothless strongyle, Strongylus edentatus (fig. 18, A), contains no
teeth in its mouth cup; otherwise it is similar in appearance to the
large strongyle, although it is somewhat smaller, females being about
114 inches long. The single-toothed strongyle, Strongylus vulgaris
(fig. 18, B), is the smallest of the three species, and is from a little

20 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

over half an inch to about an inch long and less than one twenty-fifth
of an inch wide; this worm contains a single tooth in its mouth cup.
This tooth has two prominent, rounded ‘projections and on casual
examination two teeth appear to be present.

Life history —The eggs of blood strongyles are discharged into
the intestine of the host and are eliminated from the body with the
feces. (Fig. 14.) Under favorable conditions of temperature and
moisture the eggs develop rapidly on the ground and on pastures and
hatch in a day or so. The larva which emerges from each egg which
develops normally, feeds on the contents of the manure in “which it
finds itself and after it undergoes two molts in more or less rapid
succession it becomes infective. This entire development on the
ground or on pasture takes place in a week or so during the warm
months and i is delayed considerably during the cold months. Lack
of moisture is unfavorable to the developing eggs and larve, but
ordinarily there is sufficient moisture in horse feces to favor normal
development, provided the temperature is favorable. Shade affords

FIGURE 13.—Head ends of the three species of blood strongyles: A. S. edentatus;
B, S. vulgaris; C, 8. equinus. Enlarged. From Looss, 1901

protection to the eggs and larve and it is likely that direct sunlight
is more or less injurious to them.

The infective larve are very resistant to unfavorable conditions
and are probably capable of maintaining themselves on pastures for
long periods. ‘They remain ordinarily in or near the manure where
they hatch; however, they are doubtless scattered by rain and wind
and may reach places on pastures relatively remote from their
original locations. When the air is sufficiently moist so that the
grass becomes covered with a film of moisture, as happens in times
of rain, dew, or fog, the larve migrate up the grass blades and this
brings them to a favorable situation to be swallowed by horses while
grazing. So far as is known, these larve do not penetrate the skin
and must infect horses by being swallowed with grass, water, or
dry food which has become contaminated with the larve.

The course of development of these parasites after they get into
the body of horses has not been definitely ascertained; it is “known.
however, that not all larve, and perhaps none of them, go down
directly into the cecum and colon and settle there and grow to

PARASITES AND PARASITIC DISEASES OF HORSES PAM

maturity. On the contrary, the larve, after entering the body of
the horse, undergo extensive migrations which bring them to various
organs and tissues, such as the liver, pancreas, spleen, lungs, kidneys,
and other organs and tissues, from which many of the larve prob-
ably fail to get back to the large gut. However, those larvee which
return to this organ become attached to its wall and develop to
fertile maturity. The eggs which are produced by the female worms
and eliminated from the horse’s gut with the manure start the cycle
of development once more.

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Horses Lecone liifested
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Wective larvae ith ass:

Ficurn 14.—Representation of the life history of one of the blood strongyles,
S. equinus. The illustrations of the adult worms are about natural size and
those of the eggs and larve are enlarged about 75 times. ‘This iilustration is
typical of the life cycle of horse strongyles generally

From this account of the life cycle of these parasites it is evident
that horses infested with blood strongyles contaminate the pastures
on which they feed with the eggs produced by the worms, and that
the larvee which issue from the eggs and develop to the infective
stage may be swallowed by these and other horses. When horses
are kept on the same pastures year after year the number of eggs
and larvee gradually increases, and this contamination, accumulating
from year to year on a given pasture, may be highly damaging to
horses which are grazed there. Foals, in particular, suffer from
the effects of gross parasitism acquired in this manner.

22 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Symptoms and lesions.——The blood strongyles injure the wall of
the gut to which they are attached. These worms suck a tuft of
the inner wall of the gut into their mouth cups (fig. 15) and abstract
blood from this delicate lining. As the worms move from one place
to another within the gut they expose its injured wall to the entrance
of disease-producing bacteria. Bloodworms abstract blood from the
finer blood vessels in the lining of the gut, and when many worms
are present in a horse at the same time the loss of blood may be
considerable and may lead to anemia with the usual consequences
of weakness and of watery swellings (edema) in various parts of
the body. These worms also produce injuries of various sorts in
the parts of the body to which they wander, such as the liver,
pancreas, and other
organs.

One species, the
single-toothed
strongyle, is espe-
cially injurious be-
cause as an imma-
ture form it settles
in certain arteries,
especially in the an-
terior mesenteric
artery which" sup-
plies blood to the
large gut. As a re-
sult of the presence
of the worms in this
blood vessel, the
wall of the artery,
where the worms
accumulate, becomes

thickened and
Beer ta arena coectsee ace Seeing eme'de

S. equinus, with a tuft of the inner lining of gut dreiwa ably to form what

fe He see ge of the worm. Greatly enlarged. is known as an

aneurism. An
aneurism is a spindle-shaped, cylindrical, or globular dilation of a
blood vessel and often contains a heavy deposit of fibrin inside. In
the horse it may attain the size of a child’s head. (Fig. 16.)

An aneurism interferes to a considerable extent with the circula-
tion of blood through the affected artery, because the heavy deposits
of fibrin inside may almost obliterate the lumen of the blood vessel.
This condition results in a diminished blood supply to the large
intestine; when the intestine becomes anemic as a result of this it
becomes predisposed to colic, twist, and intussusception, the last
being a condition in which part of the gut slips into an adjoining
part. When a piece of fibrin deposit in the aneurism breaks loose,
it may be carried in the circulation to a terminal portion of an artery
and may lodge there as a plug. As a consequence, the circulation
to a part of the large gut may be completely shut off. Such a con-
dition interferes with the functions of the large gut, produces an
anemic condition with the consequences noted above, and in extreme

PARASITES AND PARASITIC DISEASES OF HORSES 93

cases may produce death. It is believed that most cases of colic in
horses result from such disturbances in the blood circulation of the
gut. Ifthe plug forms in a hind leg it may cause a form of intermit-
tent lameness. Aside from the injuries described, mixed parasitic
infestation, known as strongylidosis, results when blood strongyles
occur in large numbers and in association with other species of
roundworms in the large gut, particularly when horses are kept on
permanent pastures.

This condition is widespread in horses and is usually more injuri-
ous to foals and young horses than to older horses. Strongylidosis is
frequently mistaken for infectious anemia or swamp fever and cases
diagnosed as swamp fever, in many instances, have cleared up fol-
lowing the removal of worms by medicinal treatment. ‘The common

symptoms of strongylidosis are diarrhea, weakness, and emaciation.
The digestive disturbances result from the irritation to the ning

FIGURE 16.—A small aneurism of the anterior mesenteric artery of the horse,
partly cut open to show worms and the heavy deposit of fibrin inside.
The worms are immature forms of Strongylus vulgaris, Natural size

of the gut produced by the parasites. At first the diarrhea is slight
and the soft manure has a bad odor and contains poorly digested
food material; later the diarrhea becomes more pronounced, with
softer feces. The appetite, which is irregular at first, becomes poorer
and finally the horses are off feed. As a result of their weakened
condition, affected horses find difficulty in chewing, may throw out
mouthfuls of feed, and then reject feed altogether. This leads to
further emaciation which becomes very marked. As the disease pro-
gresses the bones become prominent, the coat becomes rough, the
eyes are sunken, and the animal becomes greatly weakened.
(Fig. 17.) With these symptoms there are marked changes in
various tissues and organs of the body.

The working capacity of horses which are suffering from strongy-
lidosis is decreased considerably even before the symptoms become
very pronounced, and in the absence of treatment such horses are
able to do less and less work as the disease progresses. It has been
found that when horses are treated for the removal of parasites
many of the symptoms described above disappear, the animals take

24 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

on weight, regain their working capacity, and make an all-round

improvement.

Treatment.—It is advisable to fast the animal 36 hours before
treating for large strongyles. Oil of chenopodium is effective for
their removal. This drug should be given in a dose of from 4 to
5 fluid drams (16 to 20 cubic centimeters) for a 1,000-pound animal,
or at a dose rate of 1 fluid dram (4 cubic centimeters) for each 250
pounds of weight, immediately preceded or followed by 1 quart of
raw linseed oil or by an aloes ball. Cases of excessive purgation
have been reported in some instances following the use of raw linseed
oil. It is possible that this undesirable action is due to impurities in
the product; conse-
quently a good grade
of oil should be used.
A mixture, said to be
without the undesir-
able effects of raw
linseed oil, has been
recommended as fol-
lows: For wean-
lings, castor oil, 4 to
6 ounces, and neu-
tral oul, 1 pint; for
yearlings and 2-year-
olds, castor oil, 6 to
8 ounces, and neutral
onl: dsspimt >; torso"
year-olds and older,
castor oil, 8 to 10
ounces, and neutral
oil, 114 pints.

Figure 17.—Horse suffering from gross infestation with : Carbon tetrachlo-
parasites (strongylidosis). Note marked emaciation. ride is also of value
Fe eee Ge lame removal of parasites, this for ther removal of

large strongyles. It
should be used in treating pregnant mares as oil of chenopodium is

dangerous for such animals. It may be given in doses of 6 to 12

fluid drams (25 to 50 cubic centimeters) for a 1,000-pound animal.

Normal butylidene chloride is another drug which is effective for
the removal of large strongyles. It should be given in a dose of 3
fluid ounces (90 cubic centimeters) for a 1,000- pound animal, and
followed in five hours by raw linseed oil at the rate of 1 quart per
1,000 pounds of weight. It is gales Oy that the dose of normal
butylidene chloride could be reduced to 2.5 ounces (75 cubic centi-
meters) for a 1,000-pound animal, without materially reducing the
efficacy of the drug. One treatment with any drug will not always
remove all worms present and, if necessary, tre atment may be re-
peated in from four to six weeks.

As a supplement to worm treatment, distinct benefit has been
obtained from the use of tonic drugs such as sodium cacodylate or
ferrous sulphate. Such drugs aid in the formation of red cells and
hemoglobin and assist the animal to overcome the anemia associated
with strongyle infestations. Sodium cacodylate is recommended for
use in subcutaneous injections in a dose of 45 grains in 10 cubic

PARASITES AND PARASITIC DISEASES OF HORSES 25

centimeters of distilled water once a week. Ferrous sulphate may
be given in a dose of 2 drams daily mixed with the grain feed. For
best results, these drugs should be given over a period of 6 weeks to 2
months.

Prevention.—Preventive measures designed to control strongyles
consist (1) in rotation of pastures, so far as possible, avoiding low
and wet pastures, and (2) sanitation of stables to prevent larve from
developing to the infective stage and from contaminating the feed
and water. ‘This is accomplished by daily removal of manure from
stables, supplying the feed in boxes and racks well raised above the
floor, and supplying clean water. The disposal of stable manure is an
important preventive measure, as is shown elsewhere in this circular.
Little can be accomplished in the way of pasture sanitation except on
farms where thoroughbred or other valuable horses are raised. On
these farms the removal of manure deposits from. pastures may be
practiced, as this procedure will remove almost all the parasite mate-
rial before it can develop and spread. Such a procedure is necessarily
troublesome and expensive and can be undertaken only by breeders to
whom the question of expense
is of secondary importance.
The average breeder will have
to resort to simpler and less
radical measures, such as
avoiding the overstocking of FIGURE 18.—Small strongyles of the horse
pastures, frequent rotation of
pastures, and special attention to foals. Where overstocking and the
use of wet pastures are unavoidable, and rotation is impossible,
reliance must be placed on treatment as often as necessary for control.

Horse breeders, and even the general farmer, should pay consid-
erable attention to the sanitation of paddocks in which the newly
born foals are kept. The foals should be kept there for several
weeks before they are put on pasture. Removal of manure from
the paddocks, at least once a week, will cut down the supply of eggs
and larvee to which the foals would otherwise be exposed. ‘This pre-
caution will help to tide the foals over the most critical period of
their lives.

Young animals require special care much the same as children.
Above everything else, a wholesome food supply and clean surround-
ings are the best safeguards against disease. Special precautions to
prevent foals from becoming parasitized are essential parts of sound
management in horse-breeding establishments and on the average
farm.

THB SMALL STRONGYLES

In addition to the blood strongyles or palisade worms, horses are
commonly infested with numerous closely related species of stron-
gyles, which are much smaller in most cases than blood strongyles,
though some are almost as large. (Fig.18.) These worms occur
in the colon and cecum and some of them produce visible injuries.
One species, 7’riodontophorus tenuicollis, produces rather severe
ulcers in the wall of the colon (Fig. 19), probably by means of the
sharp teeth in their mouth cups. Some of the smaller horse stron-
vyles, the many species known as cylicostomes, species of Trichonema

138442 °—37———_4

26 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

or Cylicostomum, are usually about a half inch or less in length and
grayish white in color, and occur attached to the gut wall or free in
the contents of the large intestine of the horse. These worms do not
feed on blood, at least ordinarily, but they may feed on the mucosa
of the large intestine. The immature forms of some cylicostomes
occur in nodules in the wall of the large intestine.

The small strongyles of the horse contribute to the picture of gross
parasitism, and together with the large strongyles, are responsible for
digestive disturbances, weakness, emaciation, and anemia resulting
from severe infestations with parasites.

The life histories of the smaller strongyles have not been studied
in detail, but the indicated control measures with reference to these
worms are the same as those recommended in connection with the
control of blood strongyles.

FicurE 19.—Lesions produced by one of the smaller horse strongyles: A, enlarged
view of lesion with worms, Triodontophorus tenwicollis, surrounding it; B, types
of lesions. (From Ransom and Hadwen, 1918)

Treatment.—The treatments recommended for the removal of large
strongyles are also used for the removal of small strongyles. Oil of
chenopodium and normal butylidene chloride are especially effective
against these worms. Carbon tetrachloride is less effective.

PINWORMS

The pinworms, Owyuris equi, which are commonly seen in horses
are the females. These are relatively long, whitish worms with a
very long and slender tail. (Fig. 20.) The males are small and
inconspicuous and are seldom found. The females may attain a
length of 3 to 6 inches. They occur in the large bowel.

Life history—The gravid females pass out with the manure and
then deposit their eggs, instead of depositing them in the bowel.
Sometimes the females hang on to the anal opening and extrude their
eggs in the region around the anus; the eggs may adhere in this

PARASITES AND PARASITIC DISEASES OF HORSES Zi.

region in the form of yellow crusts. In either case, the eggs develop
outside of the body, as do those of the large intestinal roundworm,
and in a few days they reach the infective stage. Each egg which
develops normally contains a small worm within the shell. Ordi-
narily the eggs do not hatch outside the horse’s body. Horses become
infested with pinworms as a result of swallowing the infective eggs
in feed or water.

Symptoms and lesions—The most evident injury produced by
pinworms is the irritation of the anus, which causes a horse to rub
its tail and buttocks against any convenient object. This irritation
may result from the passage of the worms out of the anus, from the
crushing of the female worms as they pass out, or from some irritant
property of the eggs. It is also reported that aside from causing
this irritation, pinworms are responsible for digestive disturbances,
and that, when present in large numbers, they produce anemia.

If. reatment. —Oil of chenopodium, administered as for large stron-
gyles, is effective for the removal of pinworms from the horse. Oil
of turpentine is also
an effective treatment
and should be given
in a dose of 2 fluid
ounces (60 cubic cen-
timeters) for a 1,000-
pound animal, imme-
diately preceded or
followed by 1 quart
of raw linseed oil or
by the proper dose of
the mixture of castor
oil and neutral oil, as
given under the treat-
ment for large
strongyles.

Prevention. — Pre-
ventive measures with FIGURE Bea OTE: Crue ised (females), of the
reference to the con-
trol of pinworms are similar to those recommended for the large
intestinal roundworms and for blood strongyles.

LUNGWORMS

Lungworms, Dictyocaulus arnfieldi, are long, slender, whitish
worms and range from about 1 inch to a little over 2 inches in length.
They occur in the bronchi and in the bronchioles (branches of the
bronchi).

Life history—The egg contains an embryo at the time it is depos-
ited by the female. The eggs hatch in the lungs, and presumably
the larvee are coughed up, swallowed, and eliminated from the body
with the manure. It is also likely that larve are expelled with
mucus during coughing or sneezing. In either event, the larve
undergo their development on the eround and attain the infective
stage in a few days. On the basis of what is known regarding the
method of infestation with closely related species of “lungworms

28 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

which occur in cattle and sheep, one may assume that horses be-
come infested with lungworms as a result of swallowing the infective
larvee with feed or water.

Symptoms.—When few lungworms are present in a horse, definite
symptoms are not produced. In heavy infestations the parasites
produce bronchitis, and the most outstanding symptom of this con-
dition is a cough. Excessive coughing weakens an animal, and in
severe cases it may result in death.

Treatment.—Medicinal treatment for lage ore infestation is
unsatisfactory.

Nursing treatment usually gives better results and is without harm
to the animal. Nursing treatment consists in providing nourishing
food, pure and uncontaminated drinking water, salt, clean, sanitary
quarters, and adequate shelter. The affected animals should be re-
moved from contaminated pastures and placed in lots or pastures
which are not infested with parasite eggs and larve. This plan of
treatment is designed to remove the animal from areas in which it
is subject to gross : reinfestation and improve its condition.

Prevention.—Preventive measures are similar to those recom-
mended for the control of blood strongyles and the large intestinal
roundworm. The manure must be disposed of in a manner that
keeps the infective material away from the horse.

THE NECK THREADWORM

The large ligament of the horse’s neck, known to veterinarians as
the ligamentum nuchae, is frequently parasitized by a long, slender
threadworm, Onchocerca cervicalis. The exact length of these worms
has not been determined owing to the difficulty of extracting them
from the hgament without breaking them.

Life history.—lt has been determined recently that certain biting
flies, commonly known as midges, are the intermediate hosts of this
parasite. The midges take up the larval worms in the course of
piercing the skin of infested horses and, after a period of 24 to 25
days, the infested midges contain larvee capable of infecting suscepti-
ble horses. Presumably, horses become infested as a result of being
bitten by midges harboring the infective larvee

Symptoms and. lesions.—These worms apparently act as irritants
to the tissues and thus weaken their resistance to the attacks of dis-
ease germs. There is reason to believe that this may lead to the de-
velopment of poll evil and fistulous withers.

Treatment.—Surgical and medicinal treatment may be employed
where poll evil or fistulous withers is present, but there is no treat-
ment for the destruction of the worms.

Prevention —While it is difficult to prevent horses from being
attacked by midges in localities where these pests occur, the avoidance
of swampy pastures and of pastures which contain streams should
prove beneficial in controlling the neck threadworm.

THREADWORMS OF THE ABDOMINAL CAVITY

Threadworms, Setaria equina, of the body cavity of the horse, also
known as filarids or setarids, are relatively long and slender (Fig. 21)
and occur in various locations outside the alimentary canal of the

PARASITES AND PARASITIC DISEASES OF HORSES 29

horse. The filarid of the body cavity of the horse is from a little
over 2 to about 5 inches in length and whitish in appearance and
usually occurs in the abdominal cavity, but it has also been reported
from other parts of the horse’s body. Immature forms of this
filarid, as well as of the closely related filarid of cattle, sometimes
occur in the eyes of horses as the so-called eye worm or “snake in
the eye.”

Life history.—The life history of this worm has not been definitely
ascertained. From what is known of the life histories of related
forms, occurring in other animals, it is probable that horse filarids
are transmitted by blood-sucking insects.

Symptoms and lesions —The adult worms do not appear to do
much damage and are not known to be responsible for any definite
symptoms. When the immature worms get
into the eye, which apparently occurs only
rarely in the United States, they produce con-
siderable irritation and in time may produce
blindness.

Treatment.—The presence of this parasite in
the abdominal cavity is seldom diagnosed dur-
ing life and no treatment for it is known.
When the worm is present in the eye, it may
be removed surgically under local anesthesia.

Prevention—In the absence of definite
knowledge concerning the mode of transmis-
sion of these parasites, no definite control
measures can be recommended. Measures to
prevent attacks by biting flies, the prevention
of fly breeding, and the use of fly repellents are
indicated as possibly of use, but less on account
of this parasite than for other reasons.

BOTS‘ B

Bot re macoot Soave ; 9) FIcurRE 21.—Threadworms,
Ss are £20 5 of certain flies (fig. 22) Setaria equina, of the

known as botflies. Three species of bots abdominal cavity of the
commonly occur in horses in the United States. pre* Naemmelei, 2 fe
The common botfly, Gastrophilus intestinalis,
occurs in practically all parts of the United States. The bots, or
parasitic larve, are reddish in color and are attached to the white
covering of the left sac of the stomach or along the ridge between the
right and left sacs of the stomach. The adult fly deposits its eggs on
the hairs of the inside of the front legs, breast, mane, belly, and even
the hind legs. The throat botfly, or chin fly, @. nasalis, is rather
widely distributed in the United States and is especially common in
the Rocky Mountain region. The adult fly of this species deposits its
eggs under the jaw of the horse, and in so doing causes much annoy-
ance to horses. The bots are yellowish in color and are attached to
that portion of the stomach which joins the small intestine and also
to the wall of the upper part of the intestine. The nose fly, G. hemor-
rhoidalis, has a more limited distribution than the other two species
and is mostly confined to the North Central States and certain of the

a eee ee eee ee
*For more detailed information concerning horse bots and their pr i ,
Farmers’ Bulletin 1503, The Horse Bots and Their Control. PEs Gurwen eo tee

30 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Rocky Mountain States, but it is spreading in all directions. The
adult flies of this species deposit their eggs along the edge of the lips
and cause much annoyance to horses. The nose fly is the most dan-
gerous of the botflies and is the one which is responsible for many
accidents because its annoyance makes horses panicky and causes
them to run away. ‘The bots of this species occur in the stomach and
duodenum, and when full grown also attach in the rectum.

Life history.—The eggs are glued to the hair of horses by the adult
flies. The eggs of the common horse bot are hatched apparently by
the biting and licking of the horse, and are taken into the mouth on
the lips and tongue. The small spiny bots burrow into the mucous
membrane of the mouth, especially the tongue, where they remain
from 21 to 28 days before emerging and passing on to the stomach.

FIGURE 22.—Portion of a horse’s stomach, showing bots, Gastrophilus intestinalis,
attached to the inner lining of the stomach wall. Natural size

The habits of the nose bot are apparently very similar to those of the
common bot. The eggs of the chin fly hatch without friction and the
young bots crawl to and enter the mouth. Whether the throat bot
penetrates the tongue is not yet known. When the bots reach the
stomach they attach themselves to its wall and remain there for a
period of from 8 to 12 months, during which time they attain their
complete larval development and then pass out of the body. While
the common bot and the throat bot pass out of the body directly
with the manure, the nose bot reattaches itself to the rectum on its
way out, then becomes detached and reattaches itself to the anus,
where it may remain for three or four days, and finally drops to the
ground. Usually all fully developed bots pass out of the body by
October and those which overwinter in the horse are the young forms.
These bots pupate in the ground and 20 to 70 days later emerge as

PARASITES AND PARASITIC DISEASES OF HORSES 31

winged flies, ready to mate and to begin the process of egg laying
once more.

Symptoms and lesions —Bots often occur in large numbers, and it
is not unusual to find several hundred of these maggots attached to
the stomach wall of a horse. These parasites have large mouth
hooks by means of which they attach themselves to the lining of the
stomach and upper intestine. They also bear spines on much of their
body surface. With this armature they are capable of irritating the
lining of the digestive tract with which they are in contact and of
producing considerable irritation and injury. The attachment of
nose bots to the rectum and edge of the anus before they pass out is
very annoying and horses have been known to dislocate bones in the
tail in their attempts to obtain relief from this annoyance.

The damage caused by the adult flies, especially the nose fly, is
very great. Runaways may lead to serious accidents and farming is
often interrupted by the inability to work the frightened horses.

Treatment—Carbon disulphide is the most effective treatment for
the removal of bots. Carbon tetrachloride may also be used but is
much less effective. Both of these drugs should be used in accord-
ance with the recommendations given under the treatment for large
intestinal roundworms. In cases in which carbon disulphide is con-
traindicated, tetrachlorethylene may be used.

Tetrachlorethylene frequently will remove from 50 to 75 per cent
of the bots when the drug is used in single doses of 1 to 2.3 fluid
ounces (30 to 70 cubic centimeters) for a 1,000-pound animal after
fasting the horse 18 hours. The drug should not be accompanied by
a purgative. Cases of dizziness have been reported occasionally in
horses dosed with tetrachlorethylene, but this dizziness soon passes off.

Nose bots which have reached the rectum or anus are not amenable
to these treatments. Treatment should be administered in the winter
after the adult flies are killed by frost and all the bots are present in
the stomach or upper part of the small intestine. One month before
the internal medication an application of one of the coal-tar creosote
dips in about 2 per cent dilution to the parts of the animal bearing
the bot eggs is advised so as to destroy the eggs and thus avoid
subsequent infestation.

Prevention.—Preventive measures against infestation with bots
include the use of various protective mechanical devices to prevent
the flies from depositing their eggs on horses, shaving the hair where
the eggs have been deposited, and the destruction of the eggs by
certain medicinal applications to the skin.

DISPOSAL OF MANURE

Inasmuch as manure is the source from which horses acquire nearly
all their common parasites, either directly or indirectly, the proper
disposal of manure from stables and yards is an essential part of
sound management. Indiscriminate spreading of fresh horse ma-
nure on horse pastures to supply fertilizer is an unwise and unsafe
procedure because it disseminates infective eggs and larve of para-
sites which have developed in stables and yards. Owners of
Thoroughbred horse farms who have learned of the danger to horses
as a result of spreading fresh manure on pastures have discontinued
this practice and are discarding manure as fertilizer altogether.

32 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Such a procedure is too wasteful for farm practice, as the manure
must be utilized and is safe after it has been stored for a time.
Conditions of storage should permit the spontaneous heating process,
which is destructive to eggs and larve of parasitic worms, to act
throughout the manure for a sufficient time.

When manure is stored in open piles it heats in the middle but
remains cold on the surface. Such manure is dangerous, so far as
parasite transmission is concerned, because the eggs and larve pres-
ent on the surface of the manure pile escape destruction. It is,
therefore, important that the outer 3 or 4 inches of exposed manure
piles be turned over every week or so in order to bury the exposed
manure under the inner material of the pile and sterilize it by
heating. If this is not done, the manure should not be placed on
any field to which horses may have access even months later, as the
eggs and larve of many species of parasites are longlived and very
resistant to unfavorable influences. It has been determined that the
eggs and larve of parasites present In manure can be more certainly
and easily destroyed if the manure is stored in closed containers -
or boxes, having double walls and a double floor, with a 4 to 6 inch
space between the walls and floor filled with sawdust, and the top
of the container covered with a well-fitting lid. (Fig. 23.) It is
essential that the containers be tight in order to retain as much heat
as possible; the greater the heat developed and retained in manure
boxes the sooner the eggs and larve will be destroyed.

The sawdust acts as an insulator, but even with this precaution
it is desirable to use tongue-and-groove lumber in the construction
of manure containers in order to make them tight. Concrete boxes
will not serve, as the manure at the sides is chilled and there is not
heating enough to destroy parasites.

For practical purposes manure which has been kept in such con-
tainers for at least two weeks may be considered free from lving
egos and larve of parasites and may be safely spread on pastures.
Several manure boxes constructed on the above principles have been
in operation at the Beltsville station of the Bureau of Animal In-
dustry with successful results. These boxes have double-walled doors
to facilitate the removal of the manure after it has been sterilized.

In default of such measures, spread horse manure on fields which
are to be pastured by animals other than horses, or plow it under.

SUMMARY OF CONTROL MEASURES

The most common and most troublesome parasites of horses in
the United States live, at least part of their lives, in the digestive
tract, either free in the lumen, attached to the walls, or embedded
in the lining of the wall. These parasites produce eggs which pass
out in the manure on to pastures, the floors of stalls, and other
places. All such worm infestations in horses trace back to manure
as the original source.

Manure must be regarded as dangerous, and control measures
should be designed to prevent contaminating the feed and water
with manure so far as it is possible to do so. The following meas-
ures are designed to reduce the possibilities of gross infestations of
horses with parasites:

PARASITES AND PARASITIC DISEASES OF HORSES 33

Pastures should be stocked lightly. Heavy stocking means more
manure, and this, in turn, means a heavier concentration of parasite
eggs and larve.

Sloping hillside pastures are better than level ones. Rain and
melting snow tend to wash manure down to some extent from sloping
pastures. The bottom of a sloping pasture is dangerous because
it has a high concentration of eggs and larve. It should be fenced
off if possible.

/
\

/
\
1.

eg ttt =

A BMA NINN

FIGURE 23.—A, Box with double walls and double floor for sterilizing horse
manure; 8B, tight-fitting lid. The space between walls and floor must be
filled with sawdust to insure insulation

Rotation of pastures is desirable and should be used so far as
available pastures permit. It is important to remember that perma-
nent pastures perpetuate parasites.

Stock rotation is a sound procedure. For the most part the
parasites of cattle, sheep, and goats are not transmissible to horses,
and vice versa. Move horses to a pasture on which cattle or sheep
have been grazing and move cattle and sheep to a horse pasture in
alternate years.

34 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Keep stables clean; remove manure often, daily if possible; supply
clean bedding and change it often; and supply clean water.

Feed from boxes well raised above the ground and from overhead
racks. Do not feed from the ground, because the feed will become
contaminated with manure.

Do not spread fresh manure on pastures. Hold stable manure,
preferably in double-walled, closed containers, until it has under-
gone a heating process. If you have an open manure pile, turn the
outer few inches of the manure once a week. Bury it under the
inner portion. If you have no facilities for keeping manure, haul
it to areas used by animals other than those that produced the
manure or plow it in for field crops.

Take steps to reduce the fly nuisance by storing manure in closed
containers or use flytraps or other preventive measures recommended
by the United States Department of Agriculture.

Remember that foals require special treatment to tide them over
the eritical period of infancy. If you expect to raise sound horses,
protect the foals.

Consult a veterinarian when your horses require medicinal treat-
ment for the removal of parasites,

EXTERNAL PARASITES OF HORSES ®
HORSE LICE

Usually lice are restricted to one host species or to closely related
species, and horse lice will not live on animals other than horses,
mules, and asses. Three kinds of lice are commonly found on horses
in the United States. The first and most important of these is the
blood-sucking species known technically as Haematopinus asini.
The two other species, 77ichodectes pilosus and T. parwmpilosus,
are biting lice.

The sucking louse of the horse is easily distinguished from the
biting species. It is much larger and has a long, pointed head,
whereas the biting lice have short, blunt, rounded heads. (Figs. 24
and 25.°) The sucking louse apparently causes more damage than
the biting lice and it is more difficult to eradicate.

NATURE AND HABITS

The eggs or nits of the sucking louse are attached firmly to the
hairs, usually close to the skin, and they hatch on the animal in
from 11 to 20 days, the majority hatching in from 12 to 14 days.
The young lice reach maturity and the females begin laying eggs
when they are 11 or 12 days old. The lice pass their lives on horses,
and can live only about 2 or 3 days when off a host animal.

The biting lice of horses deposit their eggs in the same general
manner as the sucking louse. The period of incubation is probably
from 8 to 10 days. These lice may live as long as 10 days when
separated from the host animal if kept on tufts of hair, but most
of them die in 5 or 6 days.

> By Marion Imes.
® From photomicographs by W. T. Huffman, of the Bureau of Animal Industry.

i ¢

4

PARASITES AND PARASITIC DISEASES OF HORSES

do

FIGURE 24.—Sucking louse of horses (Haematopinus asini): A, Male; B, female.
(Magnified 25 times)

FicurRE 25.—Biting louse of horses (Trichodectes pilosus): A, Male; B, female.
(Magnified 25 times)

&

36 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

During cold weather, when the hair on horses is long, lice increase
very rapidly; but when the animals shed their hair in the spring
the parasites seem to disappear. Some of the lice usually remain
on the animals throughout the summer, but not in sufficient numbers
to cause annoyance or to be easily detected. The animals, therefore,
usually go into the winter infested. Since the most efficacious rem-
edies are liquid dips, which can not be used safely on horses during
cold weather, fall dipping should be practiced whenever horses have
been lousy at shedding time.

Symptoms.—The sucking louse obtains its food by puncturing the
skin of the horse and sucking blood and lymph. When not feed-
ing it moves about on the hair and skin. The biting lice do not suck
blood from the host, but apparently feed on particles of hair, scales,
and exudations from the skin. The irritation and itching which
result from either or both methods of feeding are shown by the
efforts of infested animals to obtain relief. Infested horses rub and
bite themselves, and often kick and stamp and manifest extreme
uneasiness and irritation.

The coat becomes rough; the frequent rubbing destroys the hair
in patches and often causes bruises or wounds in the skin. If lice
are present in sufficient numbers to cause considerable itching and
irritation they can usually be found, especially if the infested animal
is placed in the sunshine. All species of horse lice are easily seen
with the naked eye and often congregate in groups or colonies on
parts of the animal. The favorite locations are the sides of the
neck, around the flanks, and under the jaws. In cases of gross
infestation, however, lice may be found all over the body and legs.

When horses are lousy, close examination should be made to learn
what kind or species of lice is present. It is not especially impor-
tant, from a practical standpoint, to distinguish between the two
species of biting lice, but it 1s important to know whether the ani-
mals are infested with biting or sucking lice or with both kinds.

Method of spreading—More cases of infestation originate from
direct contact with lousy animals than in any other way. Under
reasonably good sanitary conditions stables, yards, and other prem-
ises which have contained lousy horses are not a source of great
danger to horses free from lice. It seems probable, however, that
occasionally lice may become dislodged from their host and drop on
mangers, floors, etc., and from these locations find their way to a new
host.

When separated from their host sucking lice live about three days,
the biting lice not to exceed 10 days. Ordinarily eggs are not de-
posited except on the host, but when the hair to which they are
attached is removed and kept under favorable conditions they may
continue to hatch for as long as 20 days. The newly hatched lice
live only two or three days unless they find a host. It is therefore
possible for premises to remain infested for 25 or 30 days from the
time they were occupied by infested horses. When lousy horses are
clipped the hair should be burned and the ground or floor where the
clippings dropped should be thoroughly treated with an insecticide.

Lice may be carried from one animal to another on currycombs,
brushes, and blankets, or by harness, saddles, and other equipment
moved directly from a lousy horse to one free from lice. Curry-

3)

e

PARASITES AND PARASITIC DISEASES OF HORSES BY

combs and brushes should be treated each time a horse is groomed.
Harness, saddles, blankets, and other equipment used on lousy ani-
mals should not be put on horses that are free from lice unless the
equipment has been thoroughly cleansed.

When cleaning stables and yards remove all litter and manure
down to a smooth surface, then spray well with a good insecticide.
The coal-tar cresote dips, diluted in accordance with the instruc-
tions printed on the label of the container, are suitable for ridding
premises of the lice.

Treatment.—None of the dips recommended for use in treating
horses can be depended on to eradicate lice at one dipping. The first
dipping, if properly done, will probably kill all the lice, but it may
not destroy all the eggs. The nits or eggs which survive dipping
often hatch, forming a new generation of lice. This new generation
should be destroyed by a second dipping after hatching is completed
and before the young lice become mature and begin depositing eggs.
Since these two periods overlap somewhat and vary greatly, and be-
cause the periods from hatching to egg laying are different for the
sucking and biting lice, it is impossible on this basis to calculate the
exact period that should elapse between dippings. Young lice ap-
pear on dipped animals as early as the third day after the first dip-
ping, and since the average period of maturation is about 12 days it
seems evident that the second dipping should be given in about two
weeks. Experience has shown that two dippings with an interval
of from 14 to 16 days usually can be depended on to control both
sucking and biting lice.

The dips commonly used for destroying lice on horses, mules, and
asses, named in the order of their effectiveness, are arsenical solution,
coal-tar creosote, and nicotine. ‘The arsenical solution is poisonous,
and unless handled with due precaution injury to man and animal
may result. When properly used, however, it is the most depend-
able known dip for destroying lice. The coal-tar creosote dip is ef-
fective when used in reasonably good water. ‘Two dippings, from 14
to 16 days apart, in either of these dips can usually be depended on to
eliminate horse lice. Two dippings in nicotine solution will ordi-
narily free horses from lice. On account of the difficulties in dipping
in cold weather, and the unsatisfactory nature of hand treatments,
most of them only palliative, it is advisable to dip for lice, when they
are present, in the fall of the year before the onset of cold weather.

Hand applications of dusting powders and oils and greases are
often resorted to in treating horses for lice. Some of the dusting
powders are of value in holding the parasites in check, but, as a rule,
they are not effective in controlling sucking lice. Biting lice can be
destroyed with sodium fluoride applied in the form of a powder or
mixed with water in the proportion of about 1 ounce to 1 gallon; but
sodium fluoride is not effective against sucking lice. Care should be
taken not to apply sodium fluoride too freely around the natural
body openings or where the skin is very thin and hairless, and not to
rub it into the skin. It may be applied with a dust gun, or a shaker,
or by hand. :

Oils and greases, such as crude petroleum, crank-case oils, or equal
parts of cottonseed oil and kerosene, are effective remedies for lice;
but ordinarily they are not suitable for use on horses, as they cause
the hair to come out, and they often blister the skin.

38 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Fumigating horses with the fumes from burning sulphur (sulphur
dioxide) will kill horse lice, but many of the eggs survive, and two
treatments two weeks apart are necessary to effect eradication. The
advantage of this method of treatment is that it can be used when
the weather is too cold for dipping. The disadvantages are that it
is necessary to have a gas-tight inclosure and the animal’s eyes and
nostrils must be kept away from the gas. <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
known as mites, which
live on or in the skin.
Four species of these
parasites are found on
domesticated animals,
but horses are com-
monly affected by
only ees of them.
These parasites are
classified zoologically
in three different
genera — Sarcoptes,
Psoroptes, and Cho-
rioptes. Mites of the

FIGURE 20 rst DueaeD with suphur Bas for eee yes first two genera are
and nostrils must be kept away from the gas. art o 2 . as
head not fumigated must be hand treated shown in Figures 27

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.

t)

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- : i ae
tionwonetheranimalics about tour | ‘artic. igncecee qoorcancans
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.
Unfortunately, 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.—In 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

40 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
flesh rapidly, becomes greatly weakened, and unless properly treated
may die.

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 4]

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-
hght 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 teo 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.

ia

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. Im the early stages of the disease the
lesions are not sufficiently prominent to attract attention, but the
animals rub and bite
themselves to relieve
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
gray-colored scabs.
The scabs are fre-
quently stained with
blood. In the early
stages the hairs
around the lesion
Bae be Sab FIGURE 30.—Psoroptic nOG ES) Female. (Magnified
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.—Kach species of domesticated animal has its own
peculiar 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

PARASI'TES AND PARASITIC DISEASES OF HORSES. A5

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 limited 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 mégnint)
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

Figtrp 31.—A, Ear ticks and débris from ear of animal (about natural size); B, en-
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)

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 light 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 yt
often turns its head : Te are
so that the more se- a
riously affected ear Figur 32.—Har 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

AS CIRCULAR 148, U. §. 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 an1-
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 low 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 liquid 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 sufficient 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 quid 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
mange and the ar-
senical dip for lice
and ticks.

ARSENICAL DIP

Aerecesmaie a le ci,
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- | CORTE SMA, al i
jury to man or ani- IGURE 34.—Exit SES tae een 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. (igs. 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 hable 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 lquid hme-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 lme-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 lhme-sulphur dip is made in the proportion of 12
pounds of unslaked hme (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 53

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 lmited
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

FIGuRE 86.—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
lable 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 sulphur 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 sarcoptic mange.

Before using a coal-tar creosote dip in hard or alkaline 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 liquid, 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 applied 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 chute 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

SEChCLOn IOP MAQNICULLUNGs ae. a ee ee Henry A. WALLACE.

WiideneS CCKelanins sens sas Same eee) S es M. L. Witson.

VAIS SUSUCIUG MIS COTEL CLs 1 nee a a ot tee Harry L. Brown.

DnecionlOp eR eenStOTy WW OnK aa =e Se C. W. WARBURTON.

De CHOTNO ME ATA 1UCem tye aa es Sie ye ey ee W. A. JUMP.

IDAHO. Of LOCALE ROD eee ee eee M.S. EISENHOWER.

DCE OTOP CTSOIIVEU a= me ee ee ed, W. W. STocKBERGER.

DRC ChOTROSMIUCSCOM Cae Ba eee 2 a JaMES T. JARDINE.

ISU GOU Ces es ak as ETAL Rc SIL Mastin G. WHITE.

Agricultural Adjustment Administration__._._ H. R. TouuEey, Administrator.
Bureau of Agricultural Economics_._.------ A. G. Buack, Chief.

Bureau of Agricultural Engineering -_---- S. H. McCrory, Chief.
BineauOneanimal INduUstiy= y= 2) anes JoHn R. Mouunmr, Chief.

BU COUOfeBtOlogueal wSUnvey = sa 2 ae Ira N. GaBRIELSON, Chief.
BUreaUunOjachemisthy ANG SOUSss= 2 2 2 Henry G. Kniaut, Chief.
Commodity Exchange Administration. __-_--- J. W. T. Duvet, Chief.

ESCO Of ALT Yah TG IUStiy mae e auene sae O. E. Reep, Chief.

Bureau of Entomology and Plant Quarantine. Len A. Strona, Chief.
Oficciofmexpenvmentistattonsao2 82522 88a) James T. JarpINE, Chief.

Food and Drug Administration. —~_-_-_----- WALTER G. CAMPBELL, Chief.

| ROPRORE LSD a pO Tg Oa A ae FERDINAND A. SiLcox, Chief.
Buncoumojerlome Heonomics=: 382 222222 as” LovisE STANLEY, Chief.

J LAAN CIP Ta ee en De aca ae eh a ge CLARIBEL R. Barnett, Librarian.
BUC OUOfmelanh Vast: se ee Te FREDERICK D. RicueEy, Chief.
ESUTCO UNO fi ALOLUC IUOGOS =) ake = se Tuomas H. MacDonatp, Chief.
Resettlement Administration_.__...______-_-- W. W. ALEXANDER, Administrator.
Soil Conservation Service_._...__-.------ . H. H. Bennett, Chief.
EGET SILT CO 1 eet he ee ey iy Wi.tus R. Greaa, Chief.

55

U.S. GOVERNMENT PRINTING OFFICE: 1937