progressively and is characterized by the absorption of the calcareous
or compact bony substance and the formation of enlarged, softened, and
porous bone. It is particularly manifest in the bones of the head,
causing enlargement and bulging of the face and jaws, thereby giving
rise to the terms "bighead" and "swelled head," which are applied to it.
The disease affects horses, mules, and asses of all ages, classes, and
breeds, and of both sexes, and is found under all soil, dietetic, and
climatic conditions. It may occur in sporadic form, but in certain
regions, such as South Africa, Australia, Madagascar, India, Hawaii, and
in this country it seems to be enzootic, several cases usually appearing
in the same stable or on the same farm, and numerous animals being
affected in the same district. In the United States the disease has been
found in all the States bordering the Delaware River and Chesapeake Bay,
in some of the New England States, and in many of the Southern States,
especially in low regions along the coast. In Europe the disease appears
to be quite rare, and is usually described as a form of osteomalacia, a
disease which is not uncommon among cattle of that continent. The
opinion that bighead is only a form of osteomalacia, however, can not be
accepted, nor can the infrequency of the former among European horses
and the frequency of the latter among other live stock be conceded on
the argument which has been presented, namely, that the better care
which horses receive prevents them from becoming affected. In the
Southwest, where osteomalacia, or creeps, has not infrequently been
observed among range cattle by the writer, no case of osteoporosis of
the horses using the same range has been noted, although the latter
animals are given no more attention than the cattle.
The appropriate treatment of osteomalacia in cattle is so effective that
if osteoporosis were a similar manifestation of disease a similar line
of treatment should prove equally efficacious. However, this is not the
fact. On the other hand, the occurrence of osteomalacia on old, worn-out
soil, or on land deficient in lime salts, or from eating feed lacking in
these bone-forming substances, or drinking water with a lime deficiency,
is in perfect accord with our knowledge of the disease. But osteoporosis
may occur on rich, fertile soil, in the most hygienic stables, and in
animals receiving the best of care and of bone-forming feeds with a
proper amount of mineral salts in the drinking water.
_Cause._--The cause of this disease still remains obscure, although
various theories have been advanced, some entirely erroneous, others
more or less plausible; but none of them has been established. Thus the
idea that feeding fodder and cereals poor in mineral salts and grazing
in pastures where the soil is poor in lime and phosphates will cause the
disease has been entirely disproved in many instances. Others have
considered that the disease starts as a muscular rheumatism which is
followed by an inflammatory condition of the bones, terminating in
osteoporosis. The idea that the disease is contagious has been advanced
by many writers, although no causative agent has been isolated. Numerous
experiments have been made by inoculating the blood of an affected horse
into normal horses without results. A piece of bone taken by Pearson
from the diseased lower jaw of a colt was transplanted into a cavity
made for it in the jaw of a normal horse, but without reproducing the
disease. Petrone believes that the _Micrococcus nitrificans_ causes
osteomalacia in man as a result of its producing nitrous acid, which
dissolves the calcareous tissues, and when injected into dogs in pure
culture a similar disease is produced. It is probable that if this work
is confirmed a somewhat similar causative factor will be discovered for
osteoporosis.
Elliott considers the latter disease to be of microbic origin, the
result of climatic conditions, and divides the island of Hawaii into two
districts, in one of which the rainfall is 150 inches annually, where
bighead is very prevalent, and the second of which is dry and rarely
visited by rain, where the disease is unknown. Removal of animals from
the wet to the dry district is followed by immediate improvement and
frequently by recovery. In the wet district horses in both good and bad
stables take the disease, but in the dry districts no unfavorable or
unhygienic surroundings produce the affection. As both native and
imported horses are equally susceptible, there is no indication of an
acquired immunity to be observed.
Theiler has recently stated that his experiments in transfusing blood
from diseased to normal horses were negative, and has suggested that the
causative agent may be transmitted by an intermediate host only, as in
the case of Texas fever. He draws attention to this method of spreading
East African coast fever, although blood inoculations, as in
osteoporosis, are always without result. We know that coast fever is
infectious, and that it can not be transmitted by blood inoculations,
but is conveyed with remarkable ease by ticks from diseased cattle. That
the cause has not been observed may be accounted for by its being
invisible even to the high magnification of the microscope.
On some farms and in some stables bighead is quite prevalent, a number
of cases following one after another. On one farm of Thoroughbreds in
Pennsylvania all the yearling colts and some of the aged horses were
affected during one year, and on a similar farm in Virginia a large
proportion of the horses for several years were diseased, although the
cows and sheep of this farm remained unaffected.
_Symptoms._--The commencement of the disease is usually unobserved by
the owner, and these symptoms which do develop are generally not well
marked or are misleading unless other cases have been noted in the
vicinity. Until the bones become enlarged the symptoms remain so vague
as not to be diagnosed readily. The disease may be present itself under
a variety of symptoms. If the bones of the hock become affected, the
animal will first show a hock lameness. If the long bones are involved,
symptoms of rheumatism will be the first observed, while if the dorsal
or lumbar vertebrae are affected indications of a strain of the lumbar
region are in evidence. Probably the first symptom to be noticed is a
loss of vitality combined with an irregular appetite or other digestive
disturbance and with a tendency to stumble while in action. These
earlier symptoms, however, may pass unobserved, and the appearance of an
intermittent or migratory lameness without any visible cause may be the
first sign to attract attention. This shifting and indefinite lameness,
involving first one leg and then the other, is very suggestive, and is
even more important when it is associated with a tendency to lie down
frequently in the stall and the absence of a desire to get up, or the
presence of evident pain and difficulty in arising.
About this time, or probably before, swelling of the bones of the face
and jaw, which is almost constantly present in this disease, will be
observed. The bones of the lower jaw are the most frequently involved,
and this condition is readily detected with the fingers by the bulging
ridge of the bone outside and along the lower edge of the molar teeth. A
thickening of the lower jawbone may likewise be identified by feeling on
both sides of each branch at the same time and comparing it with the
thinness of this bone in a normal horse. As a result mastication becomes
difficult or impossible and the teeth become loose and painful. The
imperfect chewing which follows causes balls of feed to form which drop
out of the mouth into the manger. Similar enlargements of the bones of
the upper jaw may be seen, causing a widening of the face and a bulging
of the bones about midway between the eyes and the nostrils. In some
cases the nasal bones also become swollen and deformed, which, together
with the bulging of the bones under the eyes, gives a good illustration
of the reason for the application of the term bighead.
Other bones of the body will undergo similar changes, but these
alterations are not so readily noted except by the symptoms they
occasion. The alterations of the bones of the spinal column and the
limbs, while difficult of observation, are nevertheless indicated by the
reluctance of the animal to get up and the desire to remain lying for
long periods of time. The animal easily tires, moves less rapidly, and
if urged to go faster may sustain a fracture or have a ligament torn
from its bony attachments, especially in the lower bones of the leg. An
affected horse weighing 1,000 pounds was seen by the writer to fracture
the large pastern bone from rearing during halter exercise.
The animal becomes poor in flesh, the coat is rough and lusterless, and
the skin tight and harsh, producing a condition termed "hidebound," with
considerable "tucking up" of the abdomen. The horse shows a short,
stilted, choppy gait, which later becomes stiffer and more restricted,
while on standing a position simulating that in founder is assumed, with
a noticeable drop to the croup. The animal at this stage usually lies
down and remains recumbent for several days at a time. Bed sores
frequently arise and fractures are not uncommon in consequence of
attempts to arise, which complications, in addition to emaciation,
result in death.
The disease may exist in this manner for variable periods extending from
two or three months to two years. The termination of the disease is
uncertain at best, but is likely to be favorable if treatment and a
change of feed, water, and location is adopted in the early stages of
the malady.
_Lesions._--As has been stated, the bones are the principal tissues
involved. The nutrition of the bone is disturbed, as is indicated by the
diminished density or rarefaction of the bony substances, the increase
in the size or widening of the Haversian canal and the medullary cavity,
and the enlargement of the network of spaces in the spongy tissue, the
absorptive changes following the course of the Haversian system. In this
process of absorption there are formed within the substance of the bone
areas of erosion, indentations, or hollow spaces of irregular shape.
These spaces increase in size and become confluent, causing an
appearance resembling some varieties of coral. The affected bone may be
readily incised with a knife, the cut surface appearing finely porous.
This porous area is soft, pliable, and yields easily to the pressure of
the finger. It has been shown by chemical analysis that the bone of an
osteoporotic horse, when compared with that of a normal horse, shows a
reduction in the amount of fat, phosphoric acid, lime, and soda, but a
slight increase in organic matter and silicic acid. The bones lose their
yellowish-white appearance, becoming gray and brittle. The affected
bones may be those of any region or portion of the body. Besides the
change already noted in the bones of the face, the ends of the long
bones, such as the ribs, are involved, and may be sectioned, though not
so readily as the facial bones. The bones of the vertebrae are also
frequently involved, necessitating great care in casting a horse, as the
writer has seen several cases of broken backs in casting such animals
for other operations. The marrow and cancellated tissue of the long
bones may contain hemorrhages and soft gelatinous material or coagulated
fibrin. The internal organs are usually normal, but a catarrhal
condition of the gastrointestinal tract may be noted as the result of
the improper mastication, resulting from the enlargement of the jaws and
soreness of the teeth.
_Treatment._--The affected animal should be immediately placed under new
conditions, both as to feed and surroundings. If the horse has been
stable fed, it is advisable to turn it out on grass for two or three
months, preferably in a higher altitude. If the disease has been
contracted while running on pasture, place the animal in the stable or
corral. In the early stages of the disease beneficial results have
followed the supplemental use of lime given in the drinking water. One
peck of lime slaked in a cask of water and additional water added from
time to time is satisfactory and can be provided at slight expense. This
treatment may be supplemented by giving a tablespoonful of powdered bone
meal in each feed, with free access to a large piece of rock salt, or
the bone meal may be given with four tablespoonfuls of molasses mixed
with the feed. Feeds containing mineral salts, such as beans, cowpeas,
oats, and cottonseed meal, may prove beneficial in replenishing the bony
substance that is being absorbed. Cottonseed meal is one of the best
feeds for this purpose, but it should be fed carefully. The animal
should not be allowed to work at all during the active stage of the
disease, nor should it be used for breeding purposes.
FOOTNOTES:
[7] This summary of symptoms is based upon work by Lingard.
HORSESHOEING.
By JOHN W. ADAMS, A. B., V. M.,
_Professor of Surgery and Lecturer on Shoeing, Veterinary Department,
University of Pennsylvania._
Bad and indifferent shoeing so frequently leads to diseases of the feet
and in irregularities of gait, which may render a horse unserviceable,
that it has been thought appropriate to conclude this book with a brief
chapter on the principles involved in shoeing healthy hoofs.
In unfolding this subject in the limited space at my disposal, I can
only hope to give the intelligent horse owner a sufficient number of
facts, based on experience and upon the anatomy and physiology of the
foot and leg, to enable him to avoid the more serious consequences of
improper shoeing.
Let us first examine this vital mechanism, the foot, and learn something
of its structure and of the natural movements of its component parts,
that we may be prepared to recognize deviations from the normal and to
apply the proper corrective.
GROSS ANATOMY OF THE FOOT.
(Pls. XXXII-XXXIV.)
The bones of the foot are four in number, three of which--the long
pastern, short pastern, and coffin bone, placed end to end--form a
continuous straight column passing downward and forward from the fetlock
joint to the ground. A small accessory bone, the navicular, or
"shuttle," bone, lies crosswise in the foot between the wings of the
coffin bone and forms a part of the joint surface of the latter. The
short pastern projects about 1-/2 inches above the hoof and extends
about an equal distance to it. (See also page 395.)
The pastern and the coffin bone are held together by strong fibrous
cords passing between each two bones and placed at the sides so as not
to interfere with the forward and backward movement of the bones. The
joints are therefore hinge joints, though imperfect, because, while the
chief movements are those of extension and flexion in a single plane,
some slight rotation and lateral movements are possible.
The bones are still further bound together and supported by three long
fibrous cords, or tendons. One, the extensor tendon of the toe, passes
down the front of the pasterns and attaches to the coffin bone just
below the edge of the hair; when pulled upon by its muscle this tendon
draws the toe forward and enables the horse to place the hoof flat upon
the ground. The other two tendons are placed behind the pasterns and are
called flexors, because they flex, or bend, the pasterns and coffin bone
backward. One of the tendons is attached to the upper end of the short
pastern, while the other passes down between the heels, glides over the
under surface of the navicular bone, and attaches itself to the under
surface of the coffin bone. These two tendons not only flex, or fold up,
the foot as the latter leaves the ground during motion, but at rest
assist the suspensory ligament in supporting the fetlock joint.
The foot-axis is an imaginary line passing from the fetlock joint
through the long axes of the two pasterns and coffin bone. This
imaginary line, which shows the direction of the pasterns and coffin
bone, should always be straight--that is, never broken, either forward
or backward when viewed from the side, or inward or outward when
observed from in front. Viewed from one side, the long axis of the long
pastern, when prolonged to the ground, should be parallel to the line of
the toe. Viewed from in front, the long axis of the long pastern, when
prolonged to the ground, should cut the hoof exactly at the middle of
the toe.
Raising the heel or shortening the toe not only tilts the coffin bone
forward and makes the hoof stand steeper at the toe, but slackens the
tendon that attaches to the under surface of the coffin bone (perforans
tendon), and therefore allows the fetlock joint to sink downward and
backward and the long pastern to assume a more nearly horizontal
position. The foot-axis, viewed from one side, is now broken forward;
that is, the long pastern is less steep than the toe, and the heels are
either too long or the toe is too short. On the other hand, raising the
toe or lowering the heels of a foot with a straight foot-axis not only
tilts the coffin bone backward and renders the toe more nearly
horizontal, but tenses the perforans tendon, which then forces the
fetlock joint forward, causing the long pastern to stand steeper. The
foot-axis, seen from one side, is now broken backward--an indication
that the toe is relatively too long or that the heels are relatively too
low.
The elastic tissues of the foot are preeminently the lateral cartilages
and the plantar cushion. The lateral cartilages are two irregularly
four-sided plates of gristle, one on either side of the foot, extending
from the wings of the coffin bone backward to the heels and upward to a
distance of an inch or more above the edge of the hair, where they may
be felt by the fingers. When sound, these plates are elastic and yield
readily to moderate finger pressure, but from various causes may undergo
ossification, in which condition they are hard and unyielding. The
plantar cushion is a wedge-shaped mass of tough, elastic, fibro-fatty
tissue filling all the space between the lateral cartilages, forming the
fleshy heels and the fleshy frog, and serving as a buffer to disperse
shock when the foot is set to the ground. It extends forward underneath
the navicular bone and perforans tendon, and protects these structures
from injurious pressure from below. Instantaneous photographs show that
at speed the horse sets the heels to the ground before other parts of
the foot--conclusive proof that the function of this tough, elastic
structure is to dissipate and render harmless violent impact of the foot
with the ground.
The horn-producing membrane, or "quick," as it is commonly termed, is
merely a downward prolongation of the "derm," or true skin, and may be
conveniently called the pododerm (foot skin). The pododerm closely
invests the coffin bone, lateral cartilages, and plantar cushion, much
as a sock covers the human foot, and is itself covered by the horny
capsule, or hoof. It differs from the external skin, or hair skin, in
having no sweat or oil glands, but, like it, is richly supplied with
blood vessels and sensitive nerves. And, just as the derm of the hair
skin produces upon its outer surface layer upon layer of horny cells
(epiderm), which protect the sensitive and vascular derm, so, likewise,
in the foot the pododerm produces over its entire surface soft cells,
which, pushed away by more recent cells forming beneath, lose moisture
by evaporation and are rapidly transformed into the corneous material
which we call the hoof. It is proper to regard the hoof as a greatly
thickened epiderm having many of the qualities possessed by such
epidermal structures as hair, feathers, nails, claws, etc.
The functions of the pododerm are to produce the hoof and to unite it
firmly to the foot.
There are five parts of the pododerm, easily distinguishable when the
hoof has been removed, namely: (1) The perioplic band, a narrow ridge
from one-sixteenth to one-eighth of an inch wide, running along the edge
of the hair from one heel around the toe to the other. This band
produces the perioplic horn, the thin varnishlike layer of glistening
horn, which forms the surface of the wall or "crust," and whose purpose
seems to be to retard evaporation of moisture from the wall. (2) The
coronary band, a prominent fleshy cornice encircling the foot just below
and parallel to the perioplic band. At the heels it is reflected forward
along the sides of the fleshy frog, to become lost near the apex of this
latter structure. The coronet produces the middle layer of the wall, and
the reflexed portions produce the "bars," which are, therefore, to be
regarded merely as a turning forward of the wall. (3) The fleshy leaves,
500 to 600 in number, parallel to one another, running downward and
forward from the lower edge of the coronary band to the margin of the
fleshy sole. They produce the soft, light-colored horny leaves which
form the deepest layer of the wall, and serve as a strong bond of union
between the middle layer of the wall and the fleshy leaves with which
they dovetail. (4) The fleshy sole, which covers the entire under
surface of the foot, excepting the fleshy frog and bars. The horny sole
is produced by the fleshy sole. (5) The fleshy frog, which covers the
under surface of the plantar cushion and produces the horny frog.
The horny box or hoof consists of wall and bars, sole and frog. The wall
is all that part of the hoof which is visible when the foot is on the
ground (see fig. 8). As already stated, it consists of three layers--the
periople, the middle layer, and the leafy layer.
The bars (see fig. 1c) are forward prolongations of the wall, and are
gradually lost near the point of the frog. The angle between the wall
and a bar is called the "buttress." Each bar lies against the horny frog
on one side and incloses a wing of the sole on the other, so that the
least expansion or contraction of the horny frog separates or
approximates the bars, and through them the lateral cartilages and the
walls of the quarters. The lower border of the wall is called the
"bearing edge," and is the surface against which the shoe bears. By
dividing the entire lower circumference of the wall into five equal
parts, a toe, two side walls, and two quarters will be exhibited. The
"heels," strictly speaking, are the two rounded soft prominences of the
plantar cushion, lying one above each quarter. The outer wall is usually
more slanting than the inner, and _the more slanting half of a hoof is
always the thicker_. In front hoofs the wall is thickest at the toe and
gradually thins out toward the quarters, where in some horses it may not
exceed one-fourth of an inch. In hind hoofs there is much less
difference in thickness between the toe, side walls, and quarters. The
horny sole, from which the flakes of old horn have been removed, is
concave and about as thick as the wall at the toe. It is rough, uneven
and often covered by flakes of dead horn in process of being loosened
and cast off. Behind the sole presents an opening into which are
received the bars and horny frog. This opening divides the sole into a
body and two wings.
The periphery of the sole unites with the lower border of the wall and
bars through the medium of the white line, which is the cross section of
the leafy horn layer of the wall and of short plugs of horn which grow
down from the lower ends of the fleshy leaves. This white line is of
much importance to the shoer, since its distance from the outer border
of the hoof is the thickness of the wall, and in the white line all
nails should be driven.
The frog, secreted by the pododerm covering the plantar cushion or fatty
frog, and presenting almost the same form as the latter, lies as a soft
and very elastic wedge between the bars and between the edges of the
sole just in front of the bars. A broad and shallow depression in its
center divides it into two branches, which diverge as they pass backward
into the horny bulbs of the heel. In front of the middle cleft the two
branches unite to form the body of the frog, which ends in the point of
the frog. The bar of a bar shoe should rest on the branches of the frog.
In unshod hoofs the bearing edge of the wall, the sole, frog, and bars
are all on a level; that is, the under surface of the hoof is perfectly
flat, and each of these structures assists in bearing the body weight.
With respect to solidity, the different parts of the hoof vary widely.
The middle layer of the wall is harder and more tenacious than the sole,
for the latter crumbles away or passes off in larger or smaller flakes
on its under surface, while no such spontaneous shortening of the wall
occurs. The white line and the frog are soft-horn structures, and differ
from hard horn in that their horn cells do not under natural conditions
become hard and hornlike. They are very elastic, absorb moisture
rapidly, and as readily dry out and become hard, brittle, and easily
fissured. Horn of good quality is fine grained and tough, while bad horn
is coarse grained and either mellow and friable or hard and brittle. All
horn is a poor conductor of heat, and the harder (drier) the horn the
more slowly does it transmit extremes of temperature.
THE PHYSIOLOGICAL MOVEMENTS OF THE HOOF.