Circular No. 148

Parasites

and Parasitic Diseases

of Horses

By

BENJAMIN SCHWARTZ, Chief, Zoological Division
MARION IMES, formerly Veterinarian
and
A. O. FOSTER, Parasitologist

Zoological Division, Bureau of Animal Industry

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UNITED STATES DEPARTMENT OF AGRICULTURE

WASHINGTON, D. C.
Issued November 1930; revised July 1948

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Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

Circular No. 148
November 1930 .» Washington, D. C.

Revised July 1948

UNITED STATES DEPARTMENT OF AGRICULTURE

Parasites and Parasitic Diseases of Horses’

By BENJAMIN ScHWARTZ, Chief, Zoological Division, Marion Imus, formerly
Veterinarian, and A. O. FosteR, Parasitologist, Zoological Division, Bureau of
Animal Industry

CONTENTS

Page ‘ Page

Internal parasites of horses_____ N 1} Internal parasites of horses—Con.
Abundance and location______ 1 Disposal-ok manures =) 6 oso 34
Symptoms and damage pro- Summary of control measures. 36
duced by parasites_________ 2| External parasites of horses____.__ 37
General control measures_____ 2 orsenhices 2) ya ek ee A etonaees 37
fedicinal treatment________- 3 Jel@ras 2oaeNOS = es Se 42
RROLOZOAN seen: =o = ee 4 MRI Ckisraccmse setter er eee eee 48

WiorEmeparasites= === aaa 4 Treating horses for external
JBXO) Sia SOS ae on ke Sec nit eee 32 DETAST LCS tele ee be OE fan eh 52

INTERNAL PARASITES OF HORSES?
ABUNDANCE AND LOCATION

HE TERM PARASITE as used in this circular refers ito forms

of animal life which, ror the purpose of obtaining food and shelter,
live on or in the bodies of other animals which are larger than the para-
sites and are known as hosts. All classes of domesticated 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 injurious species. A horse’s stomach may con-
tain 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

1 This circular supersedes Farmers’ Bulletin No. 1493, Lice, Mange, and Ticks
of Horses.

2 By Benjamin Schwartz and A. O. Foster. Dr. Foster has revised most of the
section originally prepared by Dr. Willard H. Wright. Many ofthe illustrations
in this section of the circular were drawn by Joseph E. Alicata, formerly junior
zoologist.

=

AL

De CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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
progressing chain of symptoms which the owner may entirely over-
look or confuse with other conditions. The general symptoms of
worm intestation in the horse are unthriftiness, weakness, emaciation,
tucked-up flanks, distended abdomen, rough coat, whitening or bleach-
ing of the mucous membranes (noticed particularly in the mucous
lining of the eyelids and mouth), and in some cases frequent colics and
diarrhea. The appetite usually remains good and the animal 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. ‘There is evidence also that the countless small
wounds that are caused by some parasites may serve as portals of
entry for disease-producing organisms such as bacteria, and that
heavily parasitized equines may already have a lowered resistance
to disease.

GENERAL CONTROL MEASURES

Most internal 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 development 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 remove the top layer of
soil down to 10 or 12 inches once or twice a year and replace it with
clean, uncontaminated soil.

PARASITES AND PARASITIC DISEASES OF HORSES 3

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 drinking
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 parasite eggs and
larvae than those changed frequently from one pasture to another.
For this reason pastures should be changed as often as possible. The
common practice of spreading horse manure on pasture 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.

MepDIcINAL [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 is advisable that all treatments for horse parasites be
administered by a veterinarian.

The treatments recommended in this circular are, for the most
part, those which have been found by experimentation to be the
most effective for the parasite or parasites involved. Many drugs,
some of them long purported to be of value for the expulsion of
worms from the horse, have been found to be practically worthless
for this purpose when critically tested. Among such preparations
may be mentioned iron sulfate, arsenic, copper sulfate, and tartar
emetic.

4 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

It should be especially noted that some drugs, like oil of chenopodi-
um, require preparatory fasting of the animals and that some other
drugs, notably phenothiazine, do not require this regimen. If a
preliminary fasting period is necessary, one should not neglect to
allow water during this time. Moreover, safe and effective medica-
tion with any of the drugs that are used against parasites requires
close adherence to the recommended dosages and methods of admin-
istration. To keep 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. Judgment, based on experience, is a better basis for
procedure than any general rule.

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

PROTOZOA

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

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

WormM PARASITES

The worm parasites of horses are flukes, tapeworms, and round-
worms, the last-mentioned group being the most common and injuri-
ous.

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

PARASITES AND PARASITIC DISEASES OF HORSES 5

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
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
flukes require snails as intermediate hosts and occur only on pastures
sufficiently wet to favor 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 is provided with four suckers used to
attach 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. These ripe or gravid segments
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 but in view of
recent information on related species in ruminants it seems possible
that pasture mites may serve as intermediate hosts. There are claims
that this view has been experimentally confirmed.

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

The large -horse tapeworm, Anoplocephala magna (fig. 1), usually
is from 3% 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.

6 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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
three-fifths of an inch to over 3 inches long. It occurs usually in
the cecum and lower portion of the small intestine. The parasites
often become localized in a small area surrounding the opening of the

Figure 1.—Almost a gallon of large tapeworms, Anoplocephala magna, removed
postmortem from a horse. About one-half natural size. (Photograph by cour-
tesy of the Agricultural and Mechanical College of Texas.)

small intestine into the cecum, the so-called ileocecal valve region,
where they produce irritative and inflammatory changes, as well as a
rapidly growing mass of tissue which progressively obstructs the
opening of the intestine. This species is fortunately much less com-
mon in American horses than the other two species of tapeworms.
Symptoms and lesions. 9 stations no symptoms are
present. Horses which are hese infested with tapeworms may
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 ot tapeworms of this species

PARASITES AND PARASITIC DISEASES OF HORSES 7

to the wall of the cecum produces small ulcers in the regions to which
the worms are attached.

Treatment.—V ery little is known regarding treatment for tapeworms
in the horse. The following treatments have been recommended but
have not had critical test to determine their precise value.

Oil of turpentine is said to be an effective remedy. This is given in
a dose of 2 fluid ounces (60 cubic centimeters) in capsules, followed
every second day by 1 ounce (30 cubic centi-

meters) in capsule until five or six doses have LL
been given. ‘The last dose is immediately BEC= erseureo The dwart
ceded or followed by 1 quart of raw linseed oil. tapeworm Axoploce-

It would seem that the drugs used for the bea ara of
treatment of tapeworm infestation in other ‘ire

animals would offer more promise.

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 4 or 5 hours, it is advisable to ad-
minister 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 tape-
worms. 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 given
to adult horses in doses of 3 to 6 drams (10 to 20 grams) in capsules
after fasting the animal for 24 hours. The drug should be immediately
preceded or followed by 1 quart of raw linseed oil.

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

Prevention.—No definite control measures can be recommended.
It should be remembered, however, 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 larvae is concerned. 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

8 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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
larvae which have emerged
from eggs. Most round-
worms which occur in the
horse are transmitted directly
by eggs and larvae, without
the use of an intermediate
host.

ROUNDWORMS IN THE STOMACH

Two kinds of worms are

’ present in the stomach of
horses. One kind, designated
here as the large stomach

A worms, is represented by
three distinct species in the
horse; these parasites are

Figure 3.—Large stomach worms of the transmitted by fhes. The
horse. A. Habronema microstoma; others, Other kind, designated as the
H. muscae. Natural size. small stomach worm of the
horse, is represented by only

one species. The smail stomach worm is acquired by horses directly
as the result of swallowing infective larvae which occur on pastures.
The larvae 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 slender,
are whitish in color, and occur either free in the stomach, embedded
in mucus, attached to the wall of the stomach, or in tumors of the
stomach wall, for which tumors these worms are responsible.

One species, Carter’s stomach worm, Habronema muscae, of the
horse, is from about one-third inch to nearly an inch long. This par-
asite occurs free in the stomach or attached to the wall of the stomach.
A second species, the small-mouthed stomach worm, H. majus, syn-
onym H. microstoma, is similar in size and appearance to the above
species. While this form may occur free in the stomach, it is capable
of penetrating its wall and causing sores. A third species, the large-
mouthed stomach worm, H/. megastoma (= Draschia 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.

PARASITES AND PARASITIC DISEASES OF HORSES 9

Infe history (fig. 4.).—The eggs of horse stomach worms have very
ilexible 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 larvae of
Carter’s stomach worm of the horse develop for the most part in house
fiies while those of the small-mouthed stomach worms of the horse

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Figure 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.

have stable flies as their usual intermediate hosts, though they are
known to develop also in house flies and other flies. The larvae of the
large-mouthed stomach worms of the horse develop in various species
of nonbiting flies, including house flies. These larvae attain their full
growth in the flies when the latter emerge from the pupae. 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
811770°—492

10 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

larvae, which are present in the mouth parts of the insects, escape,
the heat and moisture of the horse’s body stimulating the larvae to
wriggle out of the flies. Once the larvae are on the lips they are
readily swallowed. Those larvae which get into the nasal cavities
probably wriggle into the pharynx and are also swallowed. When the
larvae 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
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
oi 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 larvae 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 effieacy for the destruction of H.
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-percent 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 disulfide 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. AH. 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 larvae of parasites is discussed subsequently in this circular.
The United States Bureau of Entomology and Plant Quarantine has
devised a trap designed 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.

The advent of DDT and some of the newer insecticides has provided
weapons of unusual value for combating flies. The spraying of stalls

PARASITES AND PARASITIC DISEASES OF HORSES Vil

and barns with suitable preparations of these materials offers promise
of being the best means of keeping fly populations at a minimum.
Sprays having prolonged insecticidal action are obtainable commercial-
ly and should be used in accordance with directions accompanying
them.

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 larvae 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.

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 larvae 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 larvae feed on the sores, the larvae escape from the mouth
parts of the fly and live for a time in the wounds. These larvae irri-
tate the sore, so that instead of healing as a simple sore it may be-
come 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 oecur in the United States, the disease has not been exten-
sively studied here, and the relation of stomach-worm larvae 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-
percent solution of formalin, applied by means of a cotton pad which
is left on the sores for 2 or 3 hours every day.

Prevention.—Skin injuries should be protected from flies by the
use of pine-tar oil or other agents to prevent their conversion into
summer sores. Flies should be controlled by the use of residual
DDT sprays or other preparations of established efficacy.

THE SMALL STOMACH WORM

This parasite, Trichostrongylus axei, occurs in the lining of the
stomach, and 1s 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

12 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

that of blood strongyles, described elsewhere in this circular, with
respect to the development of the eggs and larvae on pastures. It is
also fairly certain that infestation is direct, and results from the
swallowing, by horses, of the infective larvae 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

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

is characterized by weakness, paleness of the mucous surfaces, wast-
ing, and digestive disturbances.

Treatment.—It is seldom that specific treatment is employed to
remove or destroy these parasites. So far as is known, however,
the use of phenothiazine, as recommended for removing strongyles,
is a reasonably effective measure. There is some evidence, also, that
treatment with carbon disulfide, as described for large stomach
worms, may be effective against this species.

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,

PARASITES AND PARASITIC DISEASES OF HORSES 13

THE LARGE INTESTINAL ROUNDWORMS OR ASCARIDS

The large intestinal roundworms, Parascaris equorum, of horses
ig. 76), 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 distin-
guishable lips. Closely related worms occur
in pigs, cattle, and human beings. Ascarids
occasionally pass out of the bow cls spontane-
ously, in which 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 numbers, especially in
foals and in young horses.

Life history (fig. 7)—The female worms
produce large numbers of eggs which are
microscopic in size. The eggs are deposited
in the lumen of the horse’s intestine and are
expelled from the bowels in the manure.
Under favorable conditions of temperature
and with an adequate supply of moisture, the
egos 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 susceptible horse. The
thick eggshell protects the embryo it contains
against various unfavorable influences.

During the summer months the eggs develop
to the infective stage in about 2 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 manure to favor the develop-
ment of the eggs. Balls of manure which
appear dry on the surface commonly contain
sufficient moisture in the middle to permit
the normal development of these eggs. Ex-
cessive drying destroys the vitality of ascarid
eggs.

lf 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 wal! of the gut and migrate with the blood
stream to the liver. From this organ they
proceed in the blood stream through the

Figure 6.—The large round-
worm, Parascaris equo-
rum: A, male; B, female.
About one-half natural
size.

14 CIRCULAR 148, U. 8. DEPARTMENT OF AGRICULTURE

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 larvae

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WOUSHIAS Of COGS.

Horses becorme liyfested
as ares!) of swallaming
Wifective eggs nit

J00d or waver

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

crawl up the windpipe until they reach the back of the mouth and
are then swallowed. In getting into the small intestine from the
stomach for the second time, they settle down and develop to maturity
in from about 2 to 2 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 disturbances of various sorts and may cause colic. These
parasites frequently become entangled with one another, resulting in
large masses of worms which may plug the lumen of the intestine.
In an extreme condition 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.
In either case, a rupture of the intestinal wall would usually cause
the death of the horse.

15

PARASITES AND PARASITIC DISEASES OF HORSES

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In experimental infestations of horses with ascarids, fever and

a cough have been observed during the early stages when the worms
were present in the lungs and in the windpipe and its branches.

infestations which are acquired naturally in stables and on pastures.
Ordinarily, ascarid infestations in foals result in unthrifty animals

It is probable that similar symptoms are present in heavy ascari

with rough, staring coats, and the removal of the worms frequently

16 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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 wander-
ing larva, has the capacity for causing great damage, and that its
presence in horses, especially foals, is a possible source of danger.
Heavy infestations, in which hundreds of worms may be present,

1. Note accumulation of litter and manure.

emee

Figure 9.—Type of insanitary box stal

may cause illness and even death as a result of the horse’s absorption
of toxic products produced by the worms.

Treatment.—Carbon disulfide 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 disulfide 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 treatment.
Fats and oils should be avoided as they promote the absorption and
increase the toxicity of the carbon disulfide. Carbon disulfide
usually produces a limited area of inflammation in the stomach of
the horse. This inflammation is without serious consequences,
however, and usually disappears in the course of a week or two.

PARASITES AND PARASITIC DISEASES OF HORSES ike

Experimental investigations indicate that carbon tetrachloride is
also effective for the removal of ascarids. The animal should be
fasted 18 hours and the caron tetrachloride given in doses of from 6
to 12 fluid drams (25 to 50 cubic centimeters) 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. The saline purgatives, magnesium
sulfate (Epsom salt) and sodium sulfate (Glauber’s salt), are ordi-
narily administered to young animals in doses of one-half pound or
less, and to mature animals in doses up to 1 pound.

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, litter and manure being removed.

These precautions are designed to prevent the foals from becoming
heavily infested with ascarids at an early age, and before they have
developed the necessary reserve vitality to cope successfully with a
heavy worm infestation. When the foal is moved to a pasture it is
essential to select one which is clean and that has not been used by
horses for a year or longer. _Proper disposal of manure and sanitary
measures recommended in connection with the control of blood
strongyles will also help to prevent infestation with ascarids.

While infestations with ascarids can be acquired on pastures, and
often are so acquired, it is important to remember that ill-kept stables,
in which manure is allowed to accumulate (fig. 9), are also the sources
of heavy infestations with intestinal roundworms, pinworms, and other
threadworms. Under pasture conditions many eggs and larvae
succumb to drought and to other unfavorable influences which prevail
in the open. In manure-laden stalls parasite eggs and larvae 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 consequent gross in-
festation with these parasites (fig. 11).

STRONGYLOIDES

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

SinlaK0e= = 40== =e

18 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

are eliminated in the manure. The eggs develop very rapidly on the
ground and on pastures, and the larvae which emerge from them may
either transform directly into infective larvae which serve to infest
other foals, or may develop into free-living males and females. As a
rule both types of development take place, some larvae 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 condi-

Figure 10.—Type of sanitary watering trough.

tions, larvae emerge from these eggs. These larvae become infective
and are capable of infecting horses.

These parasites multiply very rapidly, the entire development on
the ground taking place in a few days. The infective larvae, 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 2 weeks after the larvae 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 probably 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 reinfestations
which may take place rapidly aud often, because of the brief period
required for development outside of the host. The parasites are

PARASITES AND PARASITIC DISEASES OF HORSES 19

usually embedded in the lining of the intestine and doubtless produce
considerable irritation. The fact that the infective larvae are capable
of penetrating the skin adds another complication and it is probable
that foals acquire part of their infestation while lying down on pas-

Figure 11.—Type of sanitary box stall. Note feed box and hayrack raised above
the ground.

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

Treatment.—Nothing is known concerning effective treatment for
these threadworms. In severe cases of diarrhea, in foals, caused by
this parasite, carbon tetrachloride is worthy of trial. The drug may
be used for foals at a dose rate of 0.1 cubic centimeters per kilogram

20 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

(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 1s advisable to administer a purgative 24 hours before treat-
ment, and to withhold feed until after the carbon tetrachloride has
been given. <A suitable purgative for foals consists of castor oil, 4 to
6 ounces, and neutral oi! (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

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 S. equinus; the small
ones are S. vulgaris. Natural size.

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
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 the horses, as follows:

The large strongyle, St-ongylus equinus (fig. 18, C), is from about
1% 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. 13, A), contains no teeth in its
mouth cup; otherwise it is similar in appearance to the large strongyle,

PARASITES AND PARASITIC DISEASES OF HORSES Dall

although it is somewhat smaller, females being about 1 inches long.
The single-toothed strongyle, Strongylus vulgaris (fig. 13, B), is the
smallest of the three species, and is from a little over half ap 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

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

becomes infective. This entire development on the ground or on
pasture takes place in a week or so during the warm months and is
delayed considerably during the cold months. Lack of moisture is
unfavorable to the developing eggs and larvae, but ordinarily there is
sufficient moisture in horse feces to favor normal development, pro-
vided the temperature is favorable. Shade affords protection to the
eggs and larvae and it is likely that direct sunlight is more or less
injurious to them.

The infective larvae 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
erass becomes covered with a film of moisture, as happens in times
of rain, dew, or fog, the larvae migrate up the grass blades and this
brings them to a favorable situation to be swallowed by horses while

D2, CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

crazing. So far as is known, these larvae do not penetrate the skin
and must infect horses by being swallowed with grass, water, or dry
food which has become contaminated with the larvae.

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 larvae, and perhaps none of them, go down
directly into the cecum and colon and settle there and grow to

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Figure 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 larvae are enlarged about 75 times. This illustration is typical

of the life cycle of horse strongyles generally.

maturity. On the contrary, the larvae, 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 larvae probably
fail to get back to the large gut. However, those larvae 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.

PARASITES AND PARASITIC DISEASES OF HORSES Ze

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 larvae 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 larvae gradually increases, and this contamination, accumulating

Figure 15.—Section through the wall of the large gut, showing the head end of an
attached blood strongyle, S. equinus, with a tuft of the inner lining of gut drawn
into the mouth cup of the worm. Greatly enlarged. From Wetzel, 1928.

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.

Symptoms and lesions —The blood strongyles injure the wall of the
gut to which they are attached. These worms suck a tuit of the inner
wall of the gut into their mouth cups (fig. 15) and abstract blood from
this delicate timing. 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

9A CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

a horse at the same time the loss of blood may be considerable and
may lead to anemia with the usual consequnces 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 especially injurious
because as an immature form it settles in certain arteries, especially
in the anterior mesenteric artery which supplies blood to the large
gut. As a result of the presence of the worms in this blood vessel,
the wall of the artery, where the worms accumulate, becomes thickened
and stretches considerably to form what is known as an aneurism.
An aneurism is a spindle-shaped, cylindrical, or globular dilation of a
blood vessel and often contaims a heavy deposit of fibrin inside. In
the horse it may attain the size of a child’s head (fig. 16).

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.

An aneurism interferes to a considerable extent with the circulation
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 condition interferes
with the functions of the large gut, produces an anemic condition with
the consequences noted above, and in extreme cases may produce
death. It is believed that most cases of colic in horses result from
such disturbances in the blood circulation of the gut. If the plug
forms in a hind leg it may cause a form of intermittent lameness.
Aside from the injuries described, mixed parasitic infestation, known

PARASITES AND PARASITIC DISEASES OF HORSES 25

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 injurious
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 follow-
ing the removal of worms by medicinal treatment. The common
symptoms of strongylidosis are diarrhea, weakness, and emaciation.
The digestive disturbances result from the irritation to the lining 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 progresses 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
on weight, regain their working capacity, and make general improve-
ment.

Treatment —Phenothiazine is very effective for the removal of large
strongyles and is a drug which has come into wide use as an equine
anthelmintic. The fact that horses occasionally react unfavorably to
this drug has not been fully explained, although there is evidence that
animals on a low protein diet may be more susceptible to the develop-
ment of anemia, jaundice, and other symptoms of intoxication than
animals maintained on rations of adequate protein content. During
recent years, moreover, most of the risk of employing phenothiazine
as an anthelmintic for horses has been overcome by administering
smaller doses than had been used formerly and by giving the drug in
divided doses. The optimum dose for a mature horse of average size
is about 30 grams of the chemical, and it may be administered in gelatin
capsules, as a drench in suitable suspension, or admixed with grain
feed. Moreover, if the last method is followed, effective medication
may be achieved by the administration in feed of 5 grams of pheno-
thiazine daily for from 5 to 7 days in succession as an alternative to
giving the full dose at one time, the period depending somewhat upon
the size of the animal. Preparatory fasting and purgation are not
necessary when phenothiazine is used, but it is desirable in the interests
of safety to guard against constipation when the treatment is given.
The addition of bran to the feed mixture is helpful in this respect.

Although heavily parasitized equines should be given therapeutic

811770°—494

26 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

doses of phenothiazine as described above, experience has shown that
strongyles can be kept at minimum numbers by allowing pastured
animals free access to loose mixtures containing about 1 part of pheno-
thiazine to approximately 40 parts of granular salt or mineral mixture.
It is generally necessary to encourage consumption of the mixture by
adding, from time to time, a small amount of grain feed. Animals on

Figure 17.—Horse suffering from gross infestation with parasites (strongylidosis)-
Note marked emaciation. Following treatment for the removal of parasites,
this horse made a good recovery.

such a regimen should be given some surveillance in order that thera-
peutic treatments may be given, if necessary, to animals which may
not consume sufficient amounts of the free-choice mixtures.

Another drug often used for the removal of large strongyles is oil
of chenopodium. It is very effective and usually safe, but horses
are sometimes slow to recover from the after effects of the medication.
When this drug is used, the animal should be fasted for 24 to 36
hours before treatment and the drug should be given in a dose of
from 4 to 5 fluid drams (16 to 20 cubie centimeters) for a 1,000-
pound animal, or at a dose rate of 1 fluid dram (4 cubic centimeters)

PARASITES AND PARASITIC DISEASES OF HORSES 27

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 purga-
tion have been reported in some instances following the use of raw
linseed oil. It is possible that this undesirable action is due to im-
purities in the product; consequently a good grade of oil should be
used. A mixture, said to be without the undesirable effects of raw
linseed oil, has been recommended as follows: For weanlings, castor
oil, 4 to 6 ounces, and mineral oil, 1 pint; for yearlings and 2-year-olds,
castor oil, 6 to 8 ounces, and mineral oil, 1 pint; for 3-year-olds and
older, castor oil, 8 to 10 ounces, and mineral oil, 114 pints.

Carbon tetrachloride also is of value for the removal of large
strongyles and is safer than oil of chenopodium for treating pregnant
mares. The dose is 6 to 12 fluid drams (25 to 50 cubic centimeters)
for a 1,000-pound animal. Normal butylidene chloride is also effec-
tive. It is administered after a preliminary fast at a dose rate of
3 fluid ounces (90 cubic centimeters) for a 1,000-pound animal, and
followed in 5 hours by 1 quart of raw linseed oil. A closely related
chemical, normal butyl chloride,
is equally effective and is less
expensive but has the disad-
vantage of being metabolized
into a very unpleasant smelling
substance. This drug is used
at a dose rate of approximately
3 fluid ounces (90 cubic centimeters) for a 1,000-pound animal and
is administered in from 8 to 10 times its volume of raw linseed oil.

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 larvae 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 material before
it can develop and spread. Such a procedure is necessarily trouble-
some and expensive and can be undertaken only by breeders to whom
the question of expense is of secondary importance. The average
breeder will have to resort to simpler and less radical measures, such
as avoiding the overstocking of pastures, frequent rotation of pastures,
and special attention to foals. Where 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 consider-
able 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 larvae to which

Figure 18.—Small strongyles of the horse.

28 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

the foals would otherwise be exposed. This precaution 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.

THE SMALL STRONGYLES

In addition to the blood strongyles or palisade worms, horses are
commonly infested with numerous closely related species of strongyles.
which are much smaller in most cases than blood strongyles, though

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

some are almost as large (fig. 18). These worms occur in the colon and
cecum and some of them produce visible injuries. One species, 77i-
odontophorus 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 strongyles, the many species
known as cylicostomes, species of Trichonema 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

PARASITES AND PARASITIC DISEASES OF HORSES | 29

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.

Treatment.—The treatments recommended for the ronoral of large
strongyles are also used for the removal of small strongyles.

PINWORMS

The pinworms, Oryuris equi, which are commonly seen in horses
are the females. These are relatively long, whitish worms with a
very long and slender
tail Giz. 20): The
males are small and in-
conspicuous and are sel-
dom found. The _ fe-
males may attain a
length of 3 to 6 inches.
They occur in the large
bowel.

Infe 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 Figure 20.—Pinworms, Oxyuris equi (females), of the
opening and_ extrude horse. Natural size.
their eggs in the region
around the anus; the eggs may adhere in this 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 infection stage. Each egg which ‘develops normally con-
tains a small worm within the shell. Ordinarily the eggs do not
hatch outside the horse’s body. Horses become infested with pin-
worms as a result of swallowing the infective eggs in feed or water.

Symptoms and lesions. The most evident injury produced by pin-
worms 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.

Treatment.—Oil of chenopodium, administered as for large stron-
gyles, is effective for the removal of pinworms from the horse. Pheno-
thiazine also is reasonably effective. Oil of turpentine is also an effec-
tive treatment and should be given in a dose of 2 fluid ounces (60 cubic
centimeters) for a 1,000-pound animal, immediately preceded or
followed by 1 quart of raw linseed oil or by the proper dose of the

30 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

mixture of castor oil and mineral oil, as given under the treatment for
large strongyles. :

Prevention.—Preventive measures with reference to the control 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
larvae are coughed up, swallowed, and eliminated from the body with
the manure. It is also likely that larvae are expelled with mucus during
coughing or sneezing. In either event, the larvae undergo their de-
velopment on the ground 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 which occur in cattle and sheep,
one may assume that horses become infested with lungworms as a
result of swallowing the infective larvae with feed or water.

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

Treatment—Medicinal treatment for lungworm 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 larvae. 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 recommended
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 ligament without breaking them.

Infe history.—It 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 larvae capable of infecting suscepti-

PARASITES AND PARASITIC DISEASES OF HORSES oil

ble horses. Presumably, horses become infested as a result of being
bitten by midges harboring the infective larvae.

Symptoms and lesions.—These worms apparently act as irritants
to the tissues and thus weaken their resistance to the attacks of disease
germs. There is reason to believe that this may lead to the develop-
ment 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 con-
tain streams should prove beneficial in con-
trolling 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 ali-
mentary canal of the 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 abdom-
inal 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 B
is known of the life histories of related forms, Figure 21.—Thread-
occurring in other animals, it is probable that worms, Setaria equi-

horse filarids are transmitted by blood-sucking are ne abdominal

insects. A, male; B, female.
Symptoms and lesions.—The adult worms do Natural size.

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 considerable irritation and in time
may produce blindness.

Treatment.—The presence of this parasite in the abdominal cavity
is seldom diagnosed during 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 transmission of these parasites, no definite control measures
can be recommended. Measures to prevent attacks by biting flies,
the prevention of fly breeding, and the reduction of flies by spraying
barns and stables with suitable preparations of DDT or other insecti-
cides may be of value.

3? CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Bots #

Bots are maggots of certain flies (fig. 22) known as botflies. Three
species of bots commonly occur in horses in the United States.

The common botfly, Gasterophilus intestinalis, occurs in practically
all parts of the United States. The bots, or parasitic larvae, 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 fiy deposits its eggs on the hairs of the inside of

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

the front legs, breast, mane, belly, and even the hind legs. The throat
botfly, or chin fly, G. nasalis, is rather widely distributed in the United
States and is especially common in the Rocky Mountain region. The
adult fiy of this species deposits its eggs under the jaw of the horse,
and in so doing causes much annoyance to horses. The bots are yellow-
ish 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. hemorrhoidalis, has a more limited distribution than

* For more detailed information concerning horse bots and their prevention
consult Farmers’ Bulletin 1503, The Horse Bots and Their Control.

PARASITES AND PARASITIC DISEASES OF HORSES 33

the other two species and is mostly confined to the North Central
States and certain of the 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 dangerous of the botflies and is the one which is responsible
for many accidents because its annoyance makes horses panicky and
causes them torunaway. The bots of this species occur in the stomach
and duodenum, and when full grown also attach in the rectum.

Life history. —The egos 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.
The habits of the nose bot are apparently very similar to those of the
common bot. The eges 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 3 or 4 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 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 pr oducing
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
oreat. Runaways may lead to serious ‘accidents and far ming is often
interrupted by the inability to work the frightened horses.

Treatment.—Carbon disulfide is the most effective treatment for
the removal of bots. Carbon tetrachloride may also be used but is
much less effective. These drugs should be used in accordance with
the recommendations given under the treatment for large intestinal
roundworms.

Tetrachlorethylene frequently will remove from 50 to 75 percent
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 purg-

34 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

ative. Cases of dizziness have been reported occasionally in horses
dosed with tetrachlorethylene, but this dizziness soon passes off.

Treatments 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. The best time is about 1 month
after the first freezing weather lasting 24 hours or longer. One month
before the internal medication an application of one of the coal-tar
creosote dips in about 2 percent 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 manure
on horse pastures to supply fertilizer is an unwise and unsafe procedure
because it disseminates infective eggs and larvae of parasites 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 dis-
carding manure as fertilizer altogether. 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 larvae 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 larvae pres-
ent on the surface of the manure pile escape destruction. It is, there-
fore, 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 larvae of
many species of parasites are longlived and very resistant to unfavor-
able influences. It has been determined that the eggs and larvae 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-fitted lid (fig. 23). It is essential that the containers be tight
in order to retain as much heat as possible; the greater the heat devel-
oped and retained in manure boxes the sooner the eggs and larvae will
be destroyed.

PARASITES AND PARASITIC DISEASES OF HORSES 35

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 2 weeks may be considered free from living eggs

——
a
(Se a ———
es Aes,

WARN /

OA ODA XN:
(KS
[fe

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

and larvae of parasites and may be safely spread on pastures. Several
manure boxes constructed on the above principles have been in opera-
tion at the Beltsville station of the Bureau of Animal Industry 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.

36 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

SUMMARY OF ContTROoL 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 measures are designed
to reduce the possibilities of gross infestations of horses with parasites:

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

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 larvae. It should be fenced off if
possible.

Rotation of pastures is desirable and should be used so far as avail-
able pastures permit. It is important to remember that permanent
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. love horses to a pasture on which cattle or sheep have been
grazing and move cattle and sheep to a horse pasture in alternate years.
_ 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, pref-
erably in double-walled, closed containers, until it has undergone 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 facillties 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 nusiance by using insecticidal sprays,
storing manure in closed containers, or employing other preventive
measures recommended by the United States Department of Agri-
culture.

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

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

PARASITES AND PARASITIC DISEASES OF HORSES 37

EXTERNAL PARASITES OF HORSES

Horst 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

A B

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

blood-sucking species known technically as Haematopinus asini. The
two other species, Bovicola pilosa and B. parumpilosa, 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 an 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.

38 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

The biting lice of horses deposit their eggs in the same general man-
ner 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.

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

A

Figure 25.—Biting louse of horses (Bovicola pilosa): A, Male; B, female,
(Magnified 25 times.)

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 remedies are
liquid dips, which cannot be used safely on horses during cold weather,
fall dipping should be practiced whenever horses have been lousy at
shedding time.

PARASITES AND PARASITIC DISEASES OF HORSES 39

Symptoms.—The sucking louse obtains its food by puncturing the
skin of the horse and sucking blood and lymph. When not feeding
it moves about on the hairand 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 them-
selves, 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 irrita-
tion they can usually be found, especially if the infested animal is
placed in the sunshine. All species of horse lice are easily seen with
the naked eye and often congregate in groups or colonies on parts of
the animal. The favorite locations are the sides of the neck, around
the flanks, and under the jaws. In cases of gross infestation, however,
lice may be found all over the body and legs.

When horses are lousy, close examination should be made to learn
what kind or species of lice is present. It is not especially impor-
tant, from. a practical standpoint, to distinguish between the two
species of biting lice, but it is important to know whether the animals
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
lee 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 3 days,
the biting lice not to exceed 10 days. Ordinarily eggs are not deposited
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 2 or
3 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. Currycombs
and brushes should be treated each time a horse is groomed. Harness,
saddles, blankets, and other equipment used on lousy animals 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 creosote dips, diluted in accordance w ith the instructions
printed on the label of the container, are suitable for ridding premises
of the lice.

40 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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 because
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 appear on
dipped animals as early as the third day after the first dipping, and
since the average period of maturation is about 12 days it seems evi-
dent that the second dipping should be given in about 2 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 dependable known
dip for destroying lice. The coal-tar creosote dip is effective 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 ordinarily 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 1s advisable to dip for lee, when they are
present, in the fall of the year before the onset of cold weather.

Applications of dusting powders or sprays are often of value for
holding lice in check. Dusting powders may be applied with a dust
gun, a shaker, or by hand, and mixtures of wettable sulfur, talc, or
pyrophyllite containing approximately 10 percent of any of the fol-
lowing insecticides are efficacious; namely, finely ground derris or
cube powder containing from 3 to’5 percent rotenone, DDT powder,
finely ground sabadilla seed, or benzene hexachloride containing at
least 10 percent of the gamma isomer. Such powders should be used
sparingly, and not allowed to get into the eyes, nose, mouth, or into
the feed of the animals. Biting lice can be destroyed with sodium
fluoride. 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.

Some of the newer insecticides which appear to be particularly
efficacious against lice, notably DDT, benzene hexachloride, and cer-
tain of the thiocyanates, are marketed in forms that are suitable for
application as sprays. These should be used according to directions
accompanying them.

Fumigating horses with the fumes from burning sulfur (sulfur
dioxide) will kill horse lice, but many of the eggs survive, and two
treatments 2 weeks apart are necessary to effect eradication. The ad-

PARASITES AND PARASITIC DISEASES OF HORSES A]

vantage 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 gastight inclosure and the animal’s eves and

Figure 26.—Fumigation with sulfur gas for lice. Eyes and nostrils must be ee
away from the gas. Part of head not fumigated must be hand treated.

nostrils must be kept away from the gas. A concentration of about
1 percent sulfur dioxide is necessary to kill the parasites, and serious
injury or death may result if the gas comes in contact with the eyes
or nostrils. After fumigation it is necessary to hand treat that part
of the head that was not fumigated (fig. 26).

42 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Hors—E 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
commonly affected by only three
of them. These parasites are classi-
fied zoologically in three different
genera—Sarcoptes, Psoroptes, and
Chorioptes. Mites of the first two
genera are 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 dis-
tinctive habits, the location and
nature of the lesions in the early
stages are more or less characteristic.
Each kind of mite, therefore, causes
a specific kind of mange which is
Figure 27.—Sarcoptic mange mite. named after the generic name of the
Female. (Magnified 100 times.) mite. Thus we have in_ horses
sarcoptic, psoroptic, and chorioptic
mange. The sarcoptic variety is the one most common on horses in
the United States

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
scabiei 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 microscope a number of short, backward-project-
ing 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 eges are laid. Each female may lay from 10 to 25 eggs during the
ege-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.

PARASITES AND PARASITIC DISEASES OF HORSES 43

As the average period of incubation on the animal is about 4 days,
and the average period after hatching until egg laying begins is 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 calcu-
lated accurately. Unfortunately, the first treatment usually does not
kill all the sarcoptic mites on the animal because of the difficulty of

ee:

oe Oe es ae Se ¥
Se ee ee Bis Lia .
Figure 28. ee mange. Head, neck, and shoulders involved.

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 5 to 7 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 on the
sensitive tissues cause great irritation and itching, and the skin be-
comes inflamed and swollen, so that small nodules are formed over and
around the burrows. As the disease develops vesicles are formed
which break and discharge serum. As the serum dries, small scabs

44 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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 underlying
tissues. The large scabs often are broken by the movements of the
animal, and blood or serum may stain the scabs a reddish yellow.

As the disease advances the skin becomes more or less bare in irregu-
lar-shaped, bald patches, and is greatly thickened and thrown into
wrinkles or folds (fig. 29). In severe cases the horse loses flesh

Figure 29.—A well-developed case of sarcoptic mange.

rapidly, becomes greatly weakened, and unless property treated
may die.

Contagiousness.—Sarcoptic mange is transmissible from one species
of animal to another, and also from animals to man. Ordinarily when
one species of animal contracts the contagion from another species the
mites live only a limited time on the new host. Sarcoptic mites of the
sheep, hog, camel, dog, cat, and rabbit may 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, espe-
cially 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.

PARASITES AND PARASITIC DISEASES OF HORSES 45

When the mites are active under favorable conditions the lesions ex-
tend rapidly, and the entire body surface may become involved in
about 6 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 sunlight
in dry places the sarcoptic mites live only a few days, but in moist,
protected places they may live 3 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, blankets, 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.—The common dips, such as lime-sulfur, 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 applications. From
four to six dippings, 5 to 7 days apart, in lime-sulfur 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 2 to 3 minutes.

Recent investigations have led to the discovery of new acaricides of
particular promise for treating certain forms of mange. Among such
substances are benzyl benzoate, tetraethylthiuram monosulfide, and
benzene hexachloride. It would be wise, therefore, for individuals
who are confronted with treating mange in horses to consult a veteri-
narian with regard to the possible applications of one of the newer
substances.

Two or more applications, a week apart, of unprocessed crude
petroleum will usually eradicate sarcoptic mange, if treatment is ap-
plied 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.

Fumigation of many horses with sulfur dioxide has been recom-
mended by some European investigators. The Bureau of Animal
Industry has conducted some field tests with this method of treatment,
but the equipment and methods of application so far devised are too
complicated and expensive for general use except where large numbers
of horses are assembled for treatment under the supervision of a
veterinarian. This method of treatment has no 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 reaching 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 imcurable by any ordinary

46 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

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 mea-
suring about one-for-
tieth and the male
about one-fiftieth of an
inch in length (fig. 30).
The entire life cycle is
passed on the host ani-
mal. Each female may
deposit from 15 to 24
eggs, which hatch in 3
to 4 days. The young
mites reach maturity,
mate, and the female
deposits eggs in from
10 to 12 days.

Dipping, if properly
done, kills all psoroptic
mites, but cannot be
depended on to destroy
the eggs. Some of the
eges may hatch after
dipping, thus forming a
new generation of mites.
To effect eradication it
is necessary to give a
second dipping after
hatching is completed
and before the young
mites reach maturity
and begin laying eggs.
It is evident that the interval between the first and second dippings
should be from 10 to 12 days.

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 secre-
tion into the wound. A shght inflammation is caused, accompanied
by an intense itching. In the early stages of the disease the lesions
are not sufficiently prominent to attract attention, but the animals rub

Figure 30.—Psoroptic mange mite. Female. (Mag-
nified 100 times.)

PARASITES AND PARASITIC DISEASES OF HORSES 47

and bite themselves to relieve the intense itching, and these symptoms
should always be investigated to learn the cause.

As the mites multiply, large numbers of small wounds are made in
the skin, followed by the formation of papules, increased 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 hardens into yellowish or gray-colored scabs. The
scabs are frequently stained with blood. In the early stages the hairs
around the lesion may be glued together in a small clump and the
nodule or scab may be about the size of a pea. As the mites con-
stantly 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 reckless
rubbing against any available surface. The uniform thickening 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 diffi-
cult to find, especially in the early stages of the disease. They are
situated in burrows under conical papillae, and by scraping the
infested area until the blood oozes from the tissue, the mites sometimes
may be found in the scrapings.

48 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

Contagiousness.—Each 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 contagious
to all classes of horses than sarcopticmange. The predisposing causes,
manner of spreading, carriers of the mites, and precautions 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 by a mite (Chorioptes equi) which closely resembles the
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 opposite
foot and often try to bite the affected parts. Some of the hair comes
out and the skin has the thickened and hardened condition character-
istic of scabies.

The remedies recommended for sarcoptic mange are effective in
eradicating foot mange. The affected areas should be well soaked in
warm lime-sulfur dip, and the treatment repeated every 10 days until
a cure is effected. Driving the horses through a shallow wading
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 some-
times 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

PARASITES AND PARASITIC DISEASES OF HORSES 49

Figure 31.—A, Ear ticks and debris 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); E, fully engorged young tick (magni-
fied 5 cee F, adult female (magnified 5 times); G, adult male (magnified
5 times).

50 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

occur more or less regularly each year. In the region infested with
cattle-fever ticks where eradication work is in progress, 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

Figure 32.—Ear probe made of baling wire.

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 (Otobius mégnini) 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, six-legged seed ticks and attach themselves in the
external canal well below the hair line, where in a week or two they
become engorged larvae. The engorged larvae molt to form nymphs
or young ticks having eight legs. The young ticks remain in the
ears from 1 to 7 months, or until fully grown and engorged, 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
3 months if no host is found.

Symptoms.—When animals are grossly infested and the ear canals
packed full ot ticks the parasites are visible on superficial examination,
but when the degree of infestation is hight 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 it head and repeatedly turns it from side to side, mean-
while inverting, or turning down, first one ear and then the other.
When irritation and itching are more intense on one side the animal
often turns it head so that the more seriously affected ear 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.

5 For more complete information, see Farmers’ Bulletin 980 entitled ‘The
Spinose Ear Tick’’ revised August 1947, by H. E. Kemper of the U. 8S. Bureau
of Animal Industry.

PARASITES AND PARASITIC DISEASES OF HORSES 51

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 bailing wire, as shown in
figure 32, the loop end being used for dislodging the ticks.

Treatment.—A widely used remedy for ear ticks 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 and stir until a uniformly smooth mixture is obtained.
When necessary 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. About one-half ounce of the
material should be put into each ear, and the ear should be held
upright for a few seconds and manipulated to force the material into
the deeper parts.

Other substances have been used, sometimes with good results.
Chloroform, for example, either undiluted or mixed with a bland oil,
is effective, but substances of this nature evaporate rapidly and
therefore afford no protection against reinfestation.

The use of pyridine in a nondrying adhesive smear has been re-
cently reeommended. The formulation used is known as‘‘Stock 1029.”
This formulation has been tested chiefly in cattle, although there can
be little doubt that it possesses a useful application to horses as well.

Another comparatively new remedy possessing effective action
against ear ticks, although lacking extensive trials in horses, contains
benzene hexachloride as the active ingredient. Under experimental
conditions, preparations consisting of 5 percent of this insecticide in
pure pine oil, or in emulsifiable petroleum oil, have offered promise of
being superior to any of the aforementioned remedies. On account of
the variable content of active insecticidal material in benzene hexa-
chloride, it is probable that the best formulations for the purpose
described will be found in preparations that are marketed or recom-
mended specifically for the destruction of ear ticks when the treat-
ment shall have progressed beyond the experimental stage.

Complete eradication of spinose ear ticks is difficult on account of
the habits of the ticks, their great vitality, and the wide range of
animals which they infest. Moreover, most horses oppose the in-
sertion of anything into their ears. Some form of restraint is almost
always necessary if treatment is to be given effectively. Farm horses
can usually be controlled with a twitch or by other common methods
of restraint, but special equipment is usually necessary for treating
range animals. An ordinary crowding chute not more than 3 or 4
feet wide is suitable for treating most horses for ear ticks. :

The only known effective method of applying treatment for the
destruction or eradication of ear ticks is to insert the remedy into the
ear passages by hand. This can be done by means of ordinary metal
or hard rubber syringes, cut-down oilers, small paint brushes, or
properly equipped knapsack sprayers. Mixtures should flow freely
and be applied in such manner as to insure complete coverage of the
deep convolutions and the inner surface of the outer ear. The mate-
rial should not be permitted to overflow, since some of the substances,

a2 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

like the pine tar-cottonseed oil mixture, may cause irritation or blister-
ing if they run down over the head and face where they are exposed to
the direct rays of the sun.

When the ear passages contain masses of hard wax and ticks, it is
desirable to clean out the material before treatment is applied. The
treatments recommended can be depended upon to kill all ticks in the
ears and to prevent reinfestation for a month or more, although the
only rule regarding the frequency of treatment is to apply the remedies
as often as necessary to keep the ears free of ticks.

Finally, it should be remembered that the eggs of ear ticks are not
deposited or hatched in the ears of animals, and that a new crop of
as ticks may find lodgment at any time on animals kept in infested
piaces.

TREATING Horses FoR ExTERNAL PARASITES

The three commonly used methods of treating horses, mules, and
asses ie 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 sulfur
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 animals
ean 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. Itis
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 oi 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
sulfur (sulfur dioxide) or some other gas. The animals to be fumi-
gated are placed in a gastight chamber with the head projecting
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
sulfur dioxide for mange apparently is about 4 percent and for lice
about 1 percent. Under ordinary conditions the concentration or

PARASITES AND PARASITIC DISEASES OF HORSES 53

percentage of gas in the air cannot be raised to more than about 1.5 or
2 percent by burning sulfur in the gas chamber unless special appa-
ratus is installed. Sulfur 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 supervise the work.
This method apparently has no other distinct advantage over dipping.

DIPPING

Dipping is the most effective known method of applying treatment
for common external parasites. Dipping plants are so arranged 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 liquid in
the vat will be lowered accordingly. The total estimated quantity
of dip which the animals carry out plus that required to charge the
vat should equal the total quantity 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.

To obtain the average length, add the length at the bottom to the
length at the dip line and divide by 2. The average width is obtained
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 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 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
projecting 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 necessary 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 2 to 4 hours before dipping, and if
Beets’ by driving they should be allowed to cool off before 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 duckings 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.

54 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

In dipping for lice it is not necessary to hold horses in the vat, but
if they have scabies they should be held in the vat 2 or 3 minutes.
After leaving the vat the animals should be held in the draining pens
until all surplus dip has drained off their bodies. Dipping should be
finished for the day early enough to dry the animals before sunset.

Before approving a dip for use in official dipping one of the require-
ments of the Bureau of Animal Industry is that there shall be 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-
sulfur, and nicotine. Of these the two most commonly used are the
lime-sulfur dip for mange and the arsenical dip for lice and ticks.

ARSENICAL DIP

Arsenical dip, when properly used, eradicates biting and sucking
lice, but it is not an effective remedy for mange. Prepared 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 suitable for use in dipping horses, mules, and asses for lice. The
instructions on the label of the container should be followed in diluting
and using ready-prepared dips. The arsenical dip is not usually
warmed or heated in the vat.

It should be remembered that arsenical dip is a poison, and precau-
tion should be taken to prevent injury to man or animal. ‘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. 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 home-made arsenical dip is preferred to the proprietary brands,
see United States Department of Agriculture Farmers’ Bulletin 1057
for full instructions for making it.

LIME-SULFUR DIP

Proprietary brands of liquid lime-sulfur may be purchased, and
many of them are equal to or even better than the home-made product.
Manufacturers have also placed on the market a product commonly
known as dry lime-sulfur, made by evaporating, in vacuo or in the
presence of an inert gas, concentrated lime-sulfur solution to which
a small amount of cane sugar has been added to act as a stabilizing
agent. Dry lime-sulfur 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-sulfur dips
are efficacious and dependable remedies for mange, but they are not
effective against lice and ticks.

Home-made lime-sulfur dip is made in the proportion of 12 pounds
of unslaked lime (or 16 pounds of commercial hydrated lime) and 24

PARASITES AND PARASITIC DISEASES OF HORSES 55

pounds of flowers of sulfur to 100 gallons of water. The lime and
sulfur 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 sulfur into the paste
and mix well with a broad hoe until a mixture of about the consistence
of mortar is formed, adding water as required. Put the mixture into
30 gallons of boiling water, adding it slowly so as not to interrupt the
boiling, and boil until the sulfur disappears from the surface. The
boiling should be continued for from 1% to 2 hours without cessation,
and the mixture stirred to prevent settlng and caking on the bottom.
When the sulfur has disappeared from the surface and the mixure
is of a chocolate of 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
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
34 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-sulfur dip in large quantities several hundred
gallons of concentrate are often made at one time in a single large
cooking tank. The quantity made at one boiling is limited only by the
facilities at hand. If the boiling tank is of sufficient capacity, a large
enough quantity of dip should be cooked at one 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-hundredths
of 1 percent nicotine. If used much stronger, they are liable to injure
horses, especially if the animals are dipped while they are warm from
exercise or hot weather.

Nicotine dips are generally used warm, but should not be heated
above 110° F. The temperature of the bath should be maintained at
90° to 95°. Sulfur is sometimes added to nicotine dips in the propor-
tion of 16 pounds of flowers of sulfur to 100 gallons of diluted dip.
The addition of sulfur 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.

56 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE

COAL-TAR CREOSOTE DIPS

The coal-tar creosote dips, commonly known as coal-tar dips, are
sold under many trade names. They are made from coal-tar deriva-
tives, and the principal ingredient is creosote oil, which is made misci-
ble 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 contamer. UH, after
standing for 1 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 separation in the dip so
tested.

The coal-tar creosote dips may be used cold or warm, but the tem-
perature 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 drainage from gasoline
motors, and other oils and greases are commenly used in treating
horses for external parasites. When properly used they will control
mange and lice, but they often mjure 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 num-
ber of horses to be dipped cattle-dipping vais usually are available,
and they can be utilized for dipping horses. 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.
In these vais the animal is placed in a movable cage and lowered into
the bath by means of a windlass or other mechanical apparatus.
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.

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