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United States. Bureau of Animal Industry.

Special report on diseases of cattle and on cattle feeding online

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diseases, and these no doubt will l>e discovered when our methods of
research are sufficiently advanced.

As the specific cause of the disease is not known, we arc, of course,
uncertain in regard to many of the characters of the virus and of the
conditions necessary for it to retain its virulence when outside of the
animal body. Some investigators and writers arc of the opinion that
the disease can only be contracted by an animal coining near enough to
a living diseased animal to receive the contagion directly from it. They
hold that the contagion is expired with the air from the affected lungs,
and that it must l>c almost immediately inspired by another animal in



380 DISEASES OF CATTLE.

order to produce the disease. Some experimental attempts to infect
animals by placing them in stables where diseased animals have been,
and by placing the diseased lungs of slaughtered animals in their feed-
ing troughs have failed, and, consequently, apparently confirm this
view.

On the other hand, it is known that the serum from affected lungs
retains its virulence and maybe used successfully for inoculation weeks
or months after the death of the animal from which it was taken. This
is particularly the case when this liquid is hermetically sealed in glass
tubes. Other investigators state that they have successfully infected
cattle by placing in the nostrils sponges or pledgets of cotton saturated
with such serum. Cattle have also, according to the best evidence
attainable, been infected from the clothing of attendants, from horns
used in drenching, and from smelling about wagons which have been
used to transport carcasses of animals affected with this disease. In
the work of eradicating pleuro-pneumonia from the United States many
stables have been found in which the disease would appear and reappear
after the slaughter of affected herds, and in spite of any precautions
which could be adopted. These were always old stables, with wood-
work in a decaying condition and with floors underlaid with filth which
could not be thoroughly removed or disinfected. In everyone of these
cases the destruction of the stable, the burning of the lumber of which
it was constructed, the removal of the accumulations beneath the floors,
and the thorough disinfection prevented the recurrence of the plague in
new stables built upon the same premises. This experience conclusively
shows that under certain conditions, at least, stables may retain the
infection for a considerable time, and that when restocked the disease
may break out again from such infection.

As a rule, however, the disease is acquired by a healthy animal being
near to an affected one and receiving the contagion direct. Affected
animals may give off the contagion in the early stages of the disease
before the symptoms are apparent to the observer, and they may retain
this infectious character, if they survive the attack, for six months and
probably for a year after all symptoms of the disease have disappeared.

Incubation. The time which elapses between exposure to the conta-
gion of pleuro-pneumonia and the first appearance of the symptoms of
this disease varies greatly with different individuals and with different
outbreaks of the disease. Ordinarily the symptoms of disease make
their appearance within from three to six weeks after exposure ; but
they may be observed within two weeks or they may not become ap-
parent until nearly or quite three months. It is this long period of
incubatfon, and the great length of time that an animal may dissemi-
nate the contagion after apparent recovery, which give the plague that
insidious character so often spoken of, and which greatly increases the
difficulties of eradication.

Symptoms. The symptoms are such as would be expected with inflani-



INFECTIOUS DISEASES OF CATTLE. 381

mat-ion of the lungs and pleurae, but they vary considerably according
To the type which the disease manifests. If the attack is anacuteone,
;is is frequently seen in hot weather, the symptoms appear suddenly,
the breathing becomes rapid and difficult, the animal grunts or moans
with each expiration, the shoulders stand out from the chest, the head
is extended on the neck, the back is arched, the temperature is 104 to
107, the milk secretion is suspended, there is no appetite, rumination
is stopped, the animal may bloat and later be affected with a severe
diarrhea. Such cases are generally fatal in from seven to twenty days.

Very often the attack comes on slowly and the symptoms are much
less clear. In the mildest cases there is a cough for a week or two, but
no appreciable loss of appetite or elevation of temperature. The lungs
are but slightly affected and recovery soon follows. Such animals may
disseminate the contagion for a long time without being suspected, and
lor that reason are the most dangerous of all.

A more severe type of the plague is the most frequently seen. In
these cases the cough is frequent, more or less painful, the back some-
what arched, and the milk secretion diminished. The prominence of
these symptoms increases, the appetite is affected, the animal loses flesh,
the breathing becomes more rapid, the cough more painful, pressure of
the fingers between the ribs shows tenderness, the hair loses its gloss
and stands erect, the skin becomes adherent, little if any milk is secreted,
and the temperature rises to 103 or 105. Animals thus affected may
continue to grow worse and die in from three to eight weeks, or they
may after a time begin to improve and make an apparent recovery.
The inflammation of the lung does not, as a rule, subside and the organ
return to its normal condition as is the case in ordinary pneumonia, but
with this disease the life of the affected portion of the lung is destroyed,
the tissue dies and a fibrous wall is formed around it to shut it away
from the living parts of the body. The tissue, thus encysted, gradu-
ally softens, becomes disintegrated and breaks down into pus. The
recovery, therefore, is not complete; it is only apparent and partial.

To tho.se accustomed to examining the lungs of cattle, other and
extremely important symptoms may be detected during the course of
the disease. By applying the ear over the walls of the chest an area
of a certain extent may be found where the natural breathing sound is
diminished or entirely lost. This represents the diseased portion of the
lungs. In other cases a loud blowing sound may be heard, quite dif-
ferent from any sound produced when the lung is in a healthy con-
dition. In some cases crepitation is heard near the border line of the
diseased area, and friction sounds produced by the roughened pleura;
but these can only be appreciated by those whose ears have been
trained to distinguish between the different sounds which reach the
ear when applied to the chest wall. By pemission, that is, by pressing
the fingers of the left hand (irmly against the wall of the chest and tup-
ping UIKIII the middle finger with the ends of the fingers of the right



382 DISEASES OF CATTLE.

hand, an area of dullness may be discovered corresponding to the por-
tion where the respiratory murmur has disappeared. This loss of res-
piration detected by ausculation, and the dullness brought out by
percussion, are the most important evidences of an inflamed or consoli-
dated lung.

Seriously affected animals remain standing, if they have sufficient
strength, but those which lie down always lie on the affected side.

The proportion of animals which become affected after being exposed
varies according to the virulence of the outbreak, the susceptibility of
the animals, and the length of time during which exposure is continued.
Sometimes not over 15, 20, or 30 per cent will contract the disease when
a large herd is exposed; but, on the other hand, 80 or 90 per cent may
be affected. The proportion of cases in which the disease proves fatal
also varies greatly it may not exceed 10 per cent and it may reach 50
per cent. In general it may be said that about 40 per cent of the
exposed animals will contract the disease and about one-half of these
cases will prove fatal.

Post-mortem appear a jwes. Owing to the complexity of the structure
of the lung tissue, its ramifications of bronchial tubes and blood-vessels
and its abundant supply of lymphatics, the pathological changes in
pleuro-pneumonia are but imperfectly understood and interpreted with
great difficulty. Our ignorance as to the nature of the exciting cause
adds to this difficulty. Furthermore there are certain kinds of pneu-
monia which present some resemblances to pleuro-pneumonia and which
may therefore be confused with it in some of its phases.

If we kill an animal affected with acute pleuro-pueumonia and exam-
ine the cavity of the chest and lungs the following appearances will be
noted:

The thorax may contain more or less serum, which may be clear or
clouded. There may be firm adhesions of different parts of the lungs to
the chest wall, the extent of which depends on the stage and severity
of the disease. The diseased lobes are unusually large and exceedingly
firm to the touch. The weight of a single large lobe may reach 40
pounds. Usually only one side is affected, often but a single lobe, and
this most commonly the large or principal lobe. The pleura may be
covered with one or more layers of a firm, elastic grayish membrane,
which varies in thickness and which sometimes may be pulled away
entirely. Sometimes it is absent. The pleura, however, is opaque and
apparently very much thickened. This is due to the diseased condition
of the connective tissue beneath the pleura, as will be explained further
on. When ail affected lobe is cut through at right angles to its long
diameter the cut surface will present a variety of interesting changes.
In the first place, the spaces between the small subdivisions of the lung
(the lobules), which in the healthy lung are barely visible, are distended
with a yellowish white, usually quite firm, substance, which is coagu-
lated fibrin. The cut surface thus appears divided up into small fields



INFECTIOUS DISEASES OF CATTLE. 383

by yellowish white bands of varying thickness running in various direc-
tions through the lung tissue and beneath the pleura. (Plate xxxii.)
These bands may appear honeycombed and the spaces filled with yel-
lowish fluid (seruin) or they may be uniformly solid. It \\ill also be
noticed that the space immediately outside of and around the artery,
vein, and air-tube is similarly broadened by fibrinous deposits. Some
authorities look upon these bands as constituting the so-called marbling
of pleuro-pneumonia.

In addition to these changes which have taken place in the connective
tissue between the lobules, the lung tissue itself may be markedly
altered. Certain areas of the cut surface may be very firm in texture
and brownish red in color. The cut surface is granular or roughened,
not smooth to the eye. Other areas equally firm may be more grayish
yellow in color, still others may be blackish. (Plate xxxui.) Besides
these areas which represent solidified (hepatized) lung tissue there may
be others which approach the normal lung tissue in color and which are
soft and float in water. From these a milky purulent fluid may often
be expressed. These different shades are represented in Plate xxxn,
Fig. 2 ? within a small compass. Some authorities are inclined to con-
sider these variations in color on the same cut surAice as the so-called
marbling^of pleuro-pneumonia. It matters not whether we regard the
bauds between the lobules or the varying shades of the lobules them-
selves as the marbling, provided either or both are peculiar to conta-
gious pleuro-pneumouia. If we examine the blood-vessels appearing
on such a cut surface they will usually be found plugged within the
firmly hepatized regions. The artery contains a dark, soft, removable
clot, the vein a grayish pink, granular, fragile plug (thrombus) which
adheres firmly to the wall of the vein, and if this be slit open, indica-
tions of a diseased condition of the inner coat will be readily detected.
When large regions of the lung tissue are hepatized the main air-tube
and its branches are usually filled with grayish, cylindrical branched
masses of fibrin easily removed, as they do not adhere to the mucous
membrane.

The views of pathologist** differ as to the nature of the earliest
changes in plenro-pneumouia, and it is not within the scope of this
work to present imperfectly developed or controverted theories. In the
foregoing description we have taken as a type the acute pleuro-pueu-
monia in its fully developed phase, which can scarcely be mistaken for
any other disease. We have seen that there is an inflammatory condi
tion of the connective tissue between the lobules, resulting in the exu-
dation of coagulahlc lymph. This inflammation is equally marked
around the blood vessels and air tubes. It leads to iniiammatory
changes in the inner wall of the veins, and these cause the dejiosition
of thrombi or plugs in the vessels, which prevent the return of the
blood. The blood pumped into the lung tissue through the artery, but
unable to get out by way of the vein, leaves the mesh work of capil-



384 DISEASES OF CATTLE.

laries around the air vesicles, enters the latter, and produces the firm
hepatized condition so characteristic of this disease. It will be easily
understood how the different shades of color from dark red to grayish
or yellowish red are produced if we bear in mind that the veins in dif-
ferent parts of the lung tissue are plugged at different times, and that,
therefore, the affected regions are in different stages of disease.

The complete plugging of the veins may lead to the death of cir-
cumscribed masses of lung tissue. A line of separation forms between
the living and the dead tissue and a thick cyst wall of fibrous tissue
forms around the latter. The dead tissue for a time preserves the
appearance of lung tissue, then undergoes disintegration and lique-
iaction. The softened mass is finally absorbed and the walls of the
cyst or capsule around it gradually collapse and form a cicatrix. This
favorable termination takes place only when the dead mass is not too
large. This may, however, involve over a half of one of the large
lobes. Under such circumstances recovery is improbable. A more
favorable termination is the abundant growth of fibrous tissue around
and into the hepatized masses. The formation of fibrous tissue may
extend to the pleura or lung covering and cause firm adhesion of the
lungs to the chest wall and to the pericardium or heart-case.

The same peculiar inflammatory changes which take place between
the lobules of the lung and around the bronchi and vessels may invade
the pleural cavity, cause extensive membranous and spongy deposits
on the pleura and firm deposits around the heart and large arteries, the
gullet, and windpipe.

These are the main features of the lung disease caused by contagious
pleuro-pneumonia. In the typical acute cases there are a sufficient
number of peculiarities to enable us to make a positive diagnosis.
There are, however, many cases in which the disease is restricted to
small areas, or to the interlobular tissue, or in which the changes are
as yet imperfectly developed, or else so far advanced that doubts may
arise as to the true nature of the affection. In such cases all obtain-
able facts, including the history of the case, the symptoms during life,
and the pathological changes observed on post-mortem examination
must be taken into consideration. Only one who has made a careful
study of the disease is fitted to decide in such cases.

Other kinds of lung disease may be confounded with pleuro-pneu-
monia because of certain features common to most lung diseases of
cattle. The inflammation of the connective tissue between the lobules
is not infrequently observed in so-called interstitial pneumonia and may
lead to the formation of whitish bands intersecting the lung tissue in
various directions. On the cut surface these bands may give rise to a
decidedly " marbled " appearance. Again, in traumatic pneumonia, due
as its name implies to the entrance of foreign bodies into the lung
tissue, generally from the paunch, the connective tissue around the
place of disease becomes inflamed and thickened and the disease itself



INFECTIOUS DISEASES OP CATTLE. 385

may simulate pleuro-pneumonia in its retrogressive stages when it is
confined to a small portion of lung tissue. The filling up of the inter-
lobular spaces with fibrin and connective tissue of inflammatory origin
is not thus limited to pleuro-pneumonia, but may appear in a marked
degree in other lung diseases. It must not be inferred from this state-
ment that these interlobular changes are necessarily the same as those
in pleuro-pneumonia, although they may appear the same to the naked
eye. We simply note their presence without discussing their nature.

In general the distinction between pleuro-pneumonia and broncho-
pneumonia is not difficult to make. In the latter disease the pneumo-
nia generally invades certain lobes as indicated by the dotted line on
Plate xxx. The disease attacks the smaller lobes in their lowest por-
tions first and gradually extends upward, '. e., toward the root of the
lung or the back of the animal and backward into the large principal
lobes. Again both lungs, in advanced cases, are often symmetrically
affected, as shown by the dotted line on both lungs in the plate referred
to. In contagions pleuro-pneumonia the large principal lobe of one
side is most frequently affected, and" a symmetrical disease of both
lungs is very rare, if, in fact, it has ever been observed. The lung
tissue in broncho-pneumonia is not enlarged, but rather more contracted
than the normal tissue around it. This is well illustrated in Plate xxxi.
Normal air-containing lobules may be scattered among and around the
hepatized portion in an irregular manner. In pleuro-pneumonia the
diseased and healthy portions are either sharply divided off, one from
the other, or else they shade into each other by intermediate stages.

The hepatized lung tissue in broncho-pneumonia when the cut sur-
face is examined is usually of a more or less dark flesh color with paler
grayish yellow dots regularly interspersed, giving it a peculiar mottled
appearance. In the more advanced stages it becomes more firm, and
may contain nodular and firmer masses disseminated through it. The
air-tubes usually contain more or less soft creamy or cheesy pus or a
turbid fluid quite different from the loose ftbrinous casts of acute pleuro-
pneumonia. The iuterlobular tissue may or may not be affected. It
sometimes contains loose tibrinous plugs, or it may be greatly distended
with air, especially in the still normal portions of the lung. The pleura
is seldom seriously diseased. If we contrast with these features the
firm, dark red hepatizations, the plugging of the veins, the extensive
intcrlobular deposits and the well-marked pleuritis in pletiro pneumo-
nia, there is little chance for confusion between well-developed cases of
the*e two lung diseases.

It should not be forjrottcn, however, that the lesions of the disease
known as contagious pleuro pneumonia may be confined to the serous
membranes of the thorax, or they may IMS confined to the parenchyma
of the lungs; they may affect a whole lobe, or only a small portion of
the lobe; they may or may not cause the so-called marbled appearance.
In the same way broncho-pneumonia may vary as to the parts of the
24097 25



386 DISEASES OF CATTLE.

lung affected, the extent of the lesions, the degree and kind of patho
logical changes in the interlobular tissue, the color of the lung on cross
section and the amount of hepatization. In individual cases, therefore,
it is often necessary in the present condition of science to take into
account the history of the animal, the course of the disease, and the
eommuuicability of the affection before a diagnosis can be made between
the two diseases.

Prevention and treatment. The prevention of pleuro-pneumouia, as of
other contagious diseases, consists in keeping animals so that they will
not be exposed to the contagion. As the disease only arises by conta-
gion; there is no possibility of an animal becoming affected with it
unless it has been exposed. If, therefore, pleuro-pneuniouia exists in
a locality the owner of healthy cattle should make every effort to keep
his animals from coming near those which are affected, or near any
which have been exposed. He should be equally particular not to allow
any person who has been on the infected premises to visit his own pas-
tures, stables, or cattle.

If pleuro-pneumonia breaks out in a herd every animal in that herd
should be slaughtered, the stables should be thoroughly cleaned and
disinfected, and no other cattle should be allowed on the premises until
a period of ninety days has elapsed.

Medical treatment of affected animals is unavailing and should not
be attempted. Xo matter how valuable the diseased animals may have
been before they contracted the disease, they should be at once destroyed
and the contagion eradicated. This is the best policy for the individ-
ual as well as for the community.

The eradication of this disease by local or national governments can
only be successful when the same principles are adopted and carried
out as are here recommended for individual stables. It is then a diffi-
cult undertaking, simply because the contagion is generally widely dis-
seminated before any measures are adopted, and because a great major-
ity of cattle-owners will never report the existence of the disease. Reg-
ulations must therefore be enforced which will insure the prompt dis-
covery of every herd in which the disease appears, as well as the
destruction of all diseased and exposed animals and the thorough disin-
fection of the premises.

To discover pleuro-pneumonia sufficiently early for this purpose the
district supposed to be infected should be clearly defined and a suffi-
cient force of inspectors should be constantly employed to inspect every
herd in that district at least once in two weeks, or better, once a week.
Ko bovine animal should be allowed to go out of the defined district
alive, and all which enter it should be carefully inspected to insure
their freedom from disease. As an assistance to the discovery of dis-
eased herds, every animal which dies in the infected district from any
cause, and every animal which is slaughtered, even if apparently in
good health, should be the subject of a careful post-mortem examination.
Many affected herds will be found in this way.



INFECTIOUS DISEASES OF CATTLE. 387

In addition to these measures it is also necessary to guard against
the removal of animals from one stable to another, and the mixing of
herds upon common pastures or in the public highways. The object
must be to isolate every individual's cattle as completely as possible, or
otherwise a single affected animal may infect a dozen or more herds.
To prevent surreptitious sale or trading of cattle, each animal must
in some way be numbered and recorded in the books kept by the official
in charge of the district. In the work of the U. S. Department of Agri-
culture a numbered metal tag has been fastened to every animal's ear,
and index books have been so arranged that with a number given the
owner could be at once ascertained, or from the owner's name the cattle
for which he was responsible could be at once learned. In this way if
an animal was missing from a stable the fact became apparent at once,
or if one animal too many was found in a stable the number in its ear
would indicate where it came from.

When pleuro-pneumonia is discovered by these means the entire
herd should be slaughtered as soon as the formalities of appraisement
can be arranged. In country districts the carcasses should be buried,
as it is generally impracticable to dispose of them in any other way.
In city districts the animals may be taken to a slaughter-house, with
such precautions as are possible to prevent dissemination of the con-
tagion. The animals should be slaughtered under the supervision of
an inspector. The healthy carcasses may be utilized for food, but the
blood, eutrailsj and all diseased carcasses should be heated to a tem-
perature equal to or above boiling water, and then used for the manu-
facture of fertilizers.

The disinfection of premises should be thorough and should be car-
ried out by a trained corps of men employed- for that purpose. The
floors of stables should be removed, the accumulations removed from



Online LibraryUnited States. Bureau of Animal IndustrySpecial report on diseases of cattle and on cattle feeding → online text (page 44 of 56)