structures inclosed within the hoof have a different position than when
not bearing weight. Since the amount of weight borne by a foot is
continually changing, and the relations of internal pressure are
continuously varying, a foot is, from a physiological viewpoint, never
at rest. The most marked changes of form of the hoof occur when the foot
bears the greatest weight, namely, at the time of the greatest descent
of the fetlock. Briefly, these changes of form are: (1) An expansion or
widening of the whole back half of the foot from the coronet to the
lower edge of the quarters. This expansion varies between one-fiftieth
and one-twelfth of an inch. (2) A narrowing of the front half of the
foot, measured at the coronet. (3) A sinking of the heels and a
flattening of the wings of the sole. These changes are more marked in
the half of the foot that bears the greater weight.
The changes of form occur in the following order. When the foot is set
to the ground the body weight is transmitted through the bones and
sensitive and horny leaves to the wall. The coffin bone and navicular
bone sink a little and rotate backward. At the same time the short
pastern sinks backward and downward between the lateral cartilages and
presses the perforans tendon upon the plantar cushion. This cushion
being compressed from above and being unable to expand downward by
reason of the resistance of the ground acting against the horny frog,
acts like any other elastic mass and expands toward the sides, pushing
before it the yielding lateral cartilages and the wall of the quarters.
This expansion of the heels is assisted and increased by the
simultaneous flattening and lateral expansion of the resilient horny
frog, which crowds the bars apart. Of course, when the lateral
cartilages are ossified, not only is no expansion of the quarters
possible, but frog pressure often leads to painful compression of the
plantar cushion and to increase of lameness. Frog pressure is therefore
contraindicated in lameness due to sidebones (ossified cartilages).
Under the descent of the coffin bone the horny sole sinks a little; that
is, the arch of the sole around the point of the frog and the wings of
the sole become somewhat flattened. All these changes of form are most
marked in sound unshod hoofs, because in them ground pressure on the
frog and sole is pronounced; they are more marked in fore hoofs than in
hind hoofs.
The movement of the different structures within the foot and the changes
of form that occur at every step are indispensable to the health of the
hoof, so that these elastic tissues must be kept active by regular
exercise, with protection against drying out of the hoof. Long-continued
rest in the stable, drying out of the hoof, and shoeing decrease or
alter the physiological movements of the hoof and sometimes lead to foot
diseases. Since these movements are complete and spontaneous only in
unshod feet, shoeing must be regarded as an evil, albeit a necessary
one, and indispensable if we wish to keep horses continuously
serviceable on hard, artificial roads. However, if in shoeing we bear in
mind the structure and functions of the hoof and apply a shoe whose
branches have a wide and level bearing surface, so as to interfere as
little as may be with the expansion and contraction of the quarters, in
so far as this is not hindered by the nails, we need not be apprehensive
of trouble, provided the horse has reasonable work and his hoofs proper
care.
GROWTH OF THE HOOF.
All parts of the hoof grow downward and forward with equal rapidity, the
rate of growth being largely dependent upon the amount of blood supplied
to the pododerm, or "quick." Abundant and regular exercise, good
grooming, moistness and suppleness of the hoof, going barefoot, plenty
of good feed, and at proper intervals removing the overgrowth of hoof
and regulating the bearing surface, by increasing the volume and
improving the quality of the blood flowing into the pododerm, favor the
rapid growth of horn of good quality; while lack of exercise, dryness of
the horn, and excessive length of the hoof hinder growth.
The average rate of growth is about one-third of an inch a month. Hind
hoofs grow faster than fore hoofs and unshod ones faster than shod ones.
The time required for the horn to grow from the coronet to the ground,
though influenced to a slight degree by the precited conditions, varies
in proportion to the distance of the coronet from the ground. At the
toe, depending on its height, the horn grows down in 11 to 13 months, at
the side wall in 6 to 8 months, and at the heels in 3 to 5 months. We
can thus estimate with tolerable accuracy the time required for the
disappearance of such defects in the hoof as cracks, clefts, etc.
Irregular growth is not infrequent. The almost invariable cause of this
is an improper distribution of the body weight over the hoof--that is,
an unbalanced foot. Colts running in soft pasture or confined for long
periods in the stable are frequently allowed to grow hoofs of excessive
length. The long toe becomes "dished"--that is, concave from the coronet
to the ground--the long quarters curl forward and inward and often
completely cover the frog and lead to contraction of the heels, or the
whole hoof bends outward or inward, and a crooked foot, or, even worse,
a crooked leg, is the result if the long hoof be allowed to exert its
powerful and abnormally directed leverage for but a few months upon
young plastic bones and tender and lax articular ligaments. All colts
are not foaled with straight legs, but failure to regulate the length
and bearing of the hoof may make a straight leg crooked and a crooked
leg worse, just as intelligent care during the growing period can
greatly improve a congenitally crooked limb. If breeders were more
generally cognizant of the power of overgrown and unbalanced hoofs to
divert the lower bones of young legs from their proper direction, and,
therefore, to cause them to be moved improperly, with loss of speed and
often with injury to the limbs, we might hope to see fewer knock-kneed,
bow-legged, "splay-footed," "pigeon-toed," cow-hocked, interfering, and
paddling horses.
If in shortening the hoof one side wall is, from ignorance, left too
long or cut down too low with relation to the other, the foot will be
unbalanced, and in traveling the long section will touch the ground
first and will continue to do so till it has been reduced to its proper
level (length) by the increased wear which will take place at this
point. While this occurs rapidly in unshod hoofs, the shoe prevents wear
of the hoof, though it is itself more rapidly worn away beneath the high
(long) side than elsewhere, so that by the time the shoe is worn out the
tread of the shoe may be flat. If this mistake be repeated from month to
month, the part of the wall left too high will grow more rapidly than
the low side whose pododerm is relatively anemic as a result of the
greater weight falling into this half of the hoof, and the ultimate
result will be a "wry," or crooked foot.
THE CARE OF UNSHOD HOOFS.
The colt should have abundant exercise on dry ground. The hoofs will
then wear gradually, and it will only be necessary from time to time to
regulate any uneven wear with the rasp and to round off the sharp edge
about the toe in order to prevent breaking away of the wall.
Colts in the stable can not wear down their hoofs, so that every four to
six weeks they should be rasped down and the lower edge of the wall well
rounded to prevent chipping. The soles and clefts of the frog should be
picked out every few days and the entire hoof washed clean. Plenty of
clean straw litter should be provided. Hoofs that are becoming "awry"
should have the wall shortened in such a manner as to straighten the
foot-axis. This will ultimately produce a good hoof and will improve the
position of the limb.
[Illustration: FIG. 1.--Ground surface of a right fore hoof of the
regular form: a, a, wall; a-a, the toe; a-b, the side walls;
b-d, the quarters; c, c, the bars; d, d, the buttress; e,
lateral cleft of the frog; f, body of the sole; g, g', g", leafy
layer (white line) of the toe and bars; h, body of the frog; i, i,
branches of the frog; k, k, horny bulbs of the heels; l, middle
cleft of the frog.]
CHARACTERISTICS OF A HEALTHY HOOF.
A healthy hoof (figs. 1 and 8) is equally warm at all parts, and is not
tender under pressure with the hands or moderate compression with
pincers. The coronet is soft and elastic at all points and does not
project beyond the surface of the wall. The wall (fig. 8) is straight
from coronet to ground, so that a straightedge laid against the wall
from coronet to ground parallel to the direction of the horn tubes will
touch at every point. The wall should be covered with the outer
varnishlike layer (periople) and should show no cracks or clefts. Every
hoof shows "ring formation," but the rings should not be strongly marked
and should always run parallel to the coronary band. Strongly marked
ring-formation over the entire wall is an evidence of a weak hoof, but
when limited to a part of the wall is evidence of previous local
inflammation. The bulbs of the heels should be full, rounded, and of
equal height. The sole (fig. 1) should be well hollowed out, the white
line solid, the frog well developed, the middle cleft of the frog broad
and shallow, the spaces between the bars and the frog wide and shallow,
the bars straight from the buttress toward the point of the frog, and
the buttresses themselves so far apart as not to press against the
branches of the frog. A hoof can not be considered healthy if it
presents reddish discolored horn, cracks in the wall, white line, bars,
or frog, thrush of the frog, contraction or displacement of the heels.
The lateral cartilages should yield readily to finger pressure.
[Illustration: FIG. 2.--Pair of fore feet of regular form in regular
standing position.]
VARIOUS FORMS OF HOOFS.
As among a thousand human faces no two are alike, so among an equal
number of horses no two have hoofs exactly alike. A little study of
different forms soon shows us, however, that the form of every hoof is
dependent in great measure on the direction of the two pastern bones as
viewed from in front or behind, or from one side; and that all hoofs
fall into three classes when we view them from in front and three
classes when we observe them in profile. Inasmuch as the form of every
foot determines the peculiarities of the shoe that is best adapted to
it, no one who is ignorant of, or who disregards the natural form of, a
hoof can hope to understand physiological shoeing.
[Illustration: FIG. 3.--Pair of fore feet of base-wide form in toe-wide
standing position.]
FORMS OF FEET VIEWED FROM IN FRONT AND IN PROFILE.
Whether a horse's feet be observed from in front or from behind, their
form corresponds to, or at least resembles, either that of the regular
position (fig. 2), the base-wide or too-wide position (fig. 3), or the
base-narrow position (fig. 4).
By the direction of the imaginary line passing through the long axes of
the two pasterns (figs. 2, 4, 5) we determine whether or not the hoof
and pasterns stand in proper mutual relation.
In the regular standing position (fig. 2) the foot-axis runs straight
downward and forward; in the base-wide position (fig. 3) it runs
obliquely downward and outward, and in the base-narrow position (fig. 4)
it runs obliquely downward and inward.
[Illustration: FIG. 4.--Pair of fore feet of base-narrow form in
toe-narrow standing position.]
Viewing the foot in profile, we distinguish the regular position (fig.
5b) and designate all forward deviations as acute-angled (long toe and
low heel, fig. 5a), and all deviations backward from the regular
(steep toe and high heel, fig. 5c) as steep-toed, or stumpy. When the
body weight is evenly distributed over all four limbs, the foot-axis
should be straight; the long pastern, short pastern, and wall at the toe
should have the same slant.
[Illustration: FIG. 5.--a, Side view of an acute-angled fore foot
(shod); b, side view of a regular fore foot, showing the most
desirable degree of obliquity (34 deg.); c, side view of a stumpy, or
"upright," fore foot; obliquity above 50 deg.. In a, b, c, note
particularly the relation between the length of the slope and the
overhanging of the heels. Note also the toe roll of the shoes.]
_A front hoof of the regular standing position._--The outer wall is a
little more slanting and somewhat thicker than the inner. The lower
border of the outer quarter describes the arc of a smaller circle--that
is, is more sharply bent than the inner quarter. The weight falls near
the center of the foot and is evenly distributed over the whole bottom
of the hoof. The toe forms an angle with the ground of 45 deg. to 50 deg. and is
parallel to the direction of the long pastern. The toe points straight
ahead, and when the horse is moving forward in a straight line the hoofs
are picked up and carried forward in a line parallel to the middle line
of the body, and are set down flat. Coming straight toward the observer
the hoofs seem to rise and fall perpendicularly.
_A hoof of the base-wide position_ is always awry. The outer wall is
more slanting, longer, and thicker than the inner, the outer quarter
more curved than the inner, and the outer half of the sole wider than
the inner. The weight falls largely into the inner half of the hoof. In
motion the hoof is moved in a circle. From its position on the ground it
breaks over the inner toe, is carried forward and inward close to the
supporting leg, thence forward and outward to the ground, which the hoof
meets first with the outer toe. Horses that are toe-wide
("splay-footed"--toes turned outward) show all these peculiarities of
hoof-form and hoof-flight to a still more marked degree and are
therefore more prone to "interfere" when in motion.
_A hoof of the base-narrow position_ is awry, but not to so marked a
degree as the base-wide hoof. The inner wall is usually a little more
slanting than the outer, the inner half of the sole wider than the
outer, and the inner quarter more curved than the outer. The outer
quarter is often flattened and drawn in at the bottom. The weight falls
largely into the outer half of the hoof. In motion the hoof breaks over
the outer toe, is carried forward and outward at some distance from the
supporting leg, thence forward and inward to the ground, which it
generally meets with the outer toe. The foot thus moves in a circle,
whose convexity is outward, a manner of flight called "paddling." A
base-narrow horse, whose toes point straight ahead, frequently
"interferes," while a toe-narrow (pigeon-toed) animal seldom does.
_A regular hoof_ (fig. 5b), viewed from one side, has a straight
foot-axis inclined to the horizon at an angle of 45 deg. to 50 deg.. The weight
falls near the center of the foot and there is moderate expansion of the
quarters.
_An acute-angled hoof_ (fig. 5a) has a straight foot-axis inclined at
an angle less than 45 deg. to the horizon. The weight falls more largely in
the back half of the hoof and there is greater length of hoof in contact
with the ground and greater expansion of the heels than in the regular
hoof.
_Upright or stumpy hoof._--In the upright or stumpy hoof (fig. 5c) the
foot-axis is straight and more than 55 deg. steep. The hoof is relatively
short from toe to heel, the weight falls farther forward, and there is
less expansion of the heels than in the regular hoof.
_Wide and narrow hoofs._--Finally, there are wide hoofs and narrow
hoofs, dependent solely upon race and breeding. The wide hoof is almost
circular on the ground surface, the sole but little concave, the frog
large, and the quality of the horn coarse. The narrow hoof has a
strongly "cupped" sole, a small frog, nearly perpendicular side walls,
and fine-grained, tough horn.
_Hind hoofs_ are influenced in shape by different directions of their
pasterns much as front feet are. A hind hoof is not round at the toe as
a front hoof is, but is more pointed. Its greatest width is two-thirds
of the way back from toe to heel, the sole is more concave, the heels
relatively wider, and the toe about 10 deg. steeper than in front hoofs.
EXAMINATION PRELIMINARY TO SHOEING.
The object of the examination is to ascertain the direction and position
of the limbs, the shape, character, and quality of the hoofs, the form,
length, position, and wear of the shoe, the number, distribution, and
direction of the nails, the manner in which the hoof leaves the ground,
its line of flight, the manner in which it is set to the ground, and all
other peculiarities, that at the next and subsequent shoeings proper
allowances may be made and observed faults corrected. The animal must,
therefore, be observed both at rest and in motion.
At rest, the observer should stand in front and note the slant of the
long pasterns. Do they drop perpendicularly, or slant downward and
outward (base-wide foot), or downward and inward (base-narrow foot)?
Whatever be the direction to the long pastern, an imaginary line passing
through its long axis, when prolonged to the ground, should apparently
pass through the middle of the toe. But if such line cuts through the
inner toe the foot-axis is not straight, as it should be, but is broken
inward at the coronet, an indication that either the outer wall of the
hoof is too long (high) or that the inner wall is too short (low). On
the contrary, if the center line of the long pastern falls through the
outer toe the foot-axis is broken outward at the coronet, an indication
that either the inner wall is too long or the outer wall too short.
The observer should now place himself at one side, two or three paces
distant, in order to view the limb and hoof in profile. Note the size of
the hoof in relation to the height and weight of the animal, and the
obliquity of the hoof. Is the foot-axis straight--that is, does the long
pastern have the same slant as the toe, or does the toe of the hoof
stand steeper than the long pastern (fig. 6c)? In which case the
foot-axis is broken forward at the coronet, an indication, usually, that
the quarters are either too high or that the toe is too short.
If the long pastern stands steeper than the toe (fig. 6a) the
foot-axis is broken backward, in which case the toe is too long or the
quarters are too low (short). In figures 6a and 6c the dotted lines
passing from toe to quarters indicate the amount of horn which must be
removed in order to straighten the foot-axis, as shown in figure 6b.
Note also the length of the shoe.
Next, the feet should be raised and the examiner should note the outline
of the foot, the conformation of the sole, form and quality of the
frog, form of the shoe, wear of the shoe, and the number and
distribution of the nails. Does the shoe fully cover the entire lower
border of the wall? or is it too narrow, or fitted so full on the inside
that it has given rise to interfering? or has the shoe been nailed on
crooked? or has it become loose and shifted? is it too short, or so wide
at the ends of the branches as not to support the buttresses of the
hoof? Does the shoe correspond with the form of the hoof? Are the nails
distributed so as to interfere as little as possible with the expansion
of the quarters? are there too many? are they too large? driven too
"fine" or too high? These are questions which the observer should put to
himself.
[Illustration: FIG. 6.--a, Side view of foot with the foot-axis broken
backward as a result of too long a toe. The amount of horn to be removed
from the toe in order to straighten the foot-axis is denoted by a dotted
line; b, side view of a properly balanced foot, with a straight
foot-axis of desirable slant; c, side view of stumpy foot with
foot-axis broken forward, as a result of overgrowth of the quarters. The
amount of horn to be removed in order to straighten the foot-axis is
shown by a dotted line.]
Note carefully the wear of the old shoe. It is the unimpeachable
evidence of the manner in which the hoof has been set to the ground
since the shoe was nailed to it, and gives valuable "pointers" in
leveling the hoof. Wear is the effect of friction between the shoe and
the ground at the moment of contact. Since the properly leveled hoof is
set flat to the ground, the "grounding wear" of a shoe should be uniform
at every point, though the toe will always show wear due to scouring at
the moment of "breaking over." Everything which tends to lengthen the
stride tends also to make the "grounding wear" more pronounced in the
heels of the shoe, while all causes which shorten the stride--as
stiffening of the limbs through age, overwork, or disease--bring the
grounding wear nearer the toe.
An exception should be noted, however, in founder, in which the
grounding wear is most pronounced at the heels.
If one branch of the shoe is found to be worn much thinner than the
other, the thinner branch has either been set too near the middle line
of the foot (fitted too close), where it has been bearing greater weight
while rubbing against the ground, or, what is much more often the case,
the section of wall above the thinner branch has been too long (too
high), or the opposite section of wall has been too short (too low).
"One-sided wear, uneven setting down of the feet, and an unnatural
course of the wall are often found together." How much an old shoe can
tell us, if we take time and pains to decipher its scars!
The horse should next be observed at a walk and at a trot or pace, from
in front, from behind, and from the side, and the "breaking over," the
carriage of the feet, and the manner of setting them to the ground
carefully noted and remembered. A horse does not always move just as his
standing position would seem to imply. Often there is so great a
difference in the form and slant of two fore hoofs or two hind hoofs
that we are in doubt as to their normal shape, when a few steps at a
trot will usually solve the problem instantly by showing us the line of
flight of the hoofs and referring them to the regular, base-wide, or
base-narrow form.
No man is competent either to shoe a horse or to direct the work till he
has made the precited observations.
PREPARATION OF THE HOOF FOR THE SHOE.
After raising the clinches of the nails with a rather dull clinch cutter
("buffer") and drawing the nails one at a time, the old shoe is
critically examined and laid aside. Remaining stubs of nails are then
drawn or punched out and the hoof freed of dirt and partially detached
horn. The farrier has now to "dress" the overgrown hoof to receive the
new shoe; in other words, he has to form a base of support so inclined
to the direction of the pasterns that in motion this surface shall be
set flat upon the ground. He must not rob the hoof nor leave too much
horn; either mistake may lead to injury. If he has made a careful
preliminary examination he knows what part of the wall requires removal
and what part must be left, for he already knows the direction of the
foot axis and the wear of the old shoe and has made up his mind just
where and how much horn must be removed to leave the hoof of proper
length and the foot axis straight.