While from the surface the hoof may appear to be a fairly simple
structure, it is actually a very complex one made up of many different
tissues, each with a specific function. Adding to the confusion regarding
the foot are the many conflicting theories concerning its care and maintenance.
This essay is designed to describe the structures of the foot, interior
and exterior, and their functions, along with some common-sense ideas
to keep the foot healthy and your horse sound.
The hoof wall is the outermost structure, a horny tissue secreted by
the coronary band. It is composed of keratinized epithelial cells arranged
into tubules running perpendicular to the ground surface of the wall.
The outer surface of the wall is covered by the periople which extends
from the coronary band down about three-quarters of an inch, except
at the heels, where it covers the heels and blends into the frog. This
material protects the junction between the hoof wall and the coronary
band. Below the periople is the stratum tectorium that continues to
the bottom of the wall. This is just a thin layer of cells, so it is
often rubbed off along the bottom by friction with dirt, grass and other
ground materials. The stratum tectorium helps control the movement of
moisture into and out of the wall. It takes approximately one year for
the hoof wall to grow from coronary band to the ground; therefore, any
changes in hoof quality will be noticeable at the top of the foot. The
wall grows evenly all the way around, so the heel (which is the shortest
area) is the youngest portion. Because the heels are the youngest, they
are also the most elastic, aiding in their expansion. The hoof wall
is the major weight-bearing surface for the horse, so should be encouraged
and allowed to grow as thick as possible.
The sole covers the bottom surface of the hoof and is about one-third
water. It is similar to the wall because it is made up of tubules; the
tubules curl near the ground surface, which explains its self-limiting
growth and causes shedding. On a healthy foot the sole will be slightly
concave, elevated off the ground. If the sole bears pressure it will
often bruise, causing lameness, and may develop into an abscess. The
bars are also on the bottom of the foot, arising from the heels where
the walls turn inward and grow along the frog. Along with the outer
wall, the bars are a weight-bearing surface. The bars need to be pared
out by the farrier periodically to prevent their overgrowing the sole.
This is called an impacted or double sole. When this occurs, the bars
grow longer and longer, folding over and eventually covering the whole
bottom of the foot, creating a great deal of pressure on the true sole.
At its extreme, the false sole connects to the hoof wall and develops
a nerve and blood supply. At this point the farrier must work very carefully
and slowly to remove the excess tissue.
The frog is the triangular mass that lies between the bars of the foot
at the heels. It is almost 50% water, and therefore is quite soft and
pliable. The point of the frog is called the apex, the grooves along
the sides are the sulci and the depression along the bottom surface
is called the central sulcus or cleft. Since it, too, is a weight-bearing
surface, the frog should be allowed to grow thick and full, even touching
the ground. Another function of the frog is to expand and contract the
heels of the foot as it moves. If the frog is not sufficient to perform
this job, contracted heels may develop. It should only be pared out
if the tissue is diseased or infected - for example, when thrush occurs.
The frog will shed itself twice a year; other than those times, the
healthy tissue should be left natural.
The corium is the vascular tissue of the foot that provides nutrition
to the other parts of the hoof. There are actually five coriums that
feed the periople, hoof wall, laminae, sole and frog. The coronary corium
lies within the coronary band and is responsible for hoof wall growth.
Injury at this point is serious and will usually lead to a defect to
the structure and future wall growth.
Inside the hoof wall is the laminae. The insensitive laminae is closest
to the wall and intermesh with the sensitive laminae. This is the support
structure for the interior of the hoof, holding the hoof wall to the
coffin bone. The laminae also help to arrange the weight to be borne
by the hoof wall, distributed over a large surface area. Where the two
layers of laminae mesh is called the white line, and can be seen on
the bottom surface of the foot. It should not be confused with the unpigmented
(white) area of the hoof wall adjacent to the white line.
There are three bones within the foot: The second phalanx (short pastern),
third phalanx (coffin bone) and the navicular bone. The coffin bone
sits mainly at the front of the foot and slightly to the outside. It
is the largest bone in the foot and appears hoof-shaped. Just above
it and connecting at the coffin joint is the short pastern, a bone that
is partly inside the hoof and partly above the coronary band. The navicular
bone is the smallest bone in the foot, lying behind the coffin joint,
where the deep digital flexor tendon runs.
Healthy feet have three requirements. The first is proper nutrition.
A balanced ration that provides all the necessary nutrients in the correct
proportions goes a long way toward promoting healthy growth. Unless
the ration is deficient in some way or the region's hay and pasture
grass lacks a needed nutrient, supplementation is usually unnecessary.
Hoof growth reflects the quality of the diet; changes in the wall will
be seen when the ration improves or falls. These changes are first seen
at the top of the hoof and then grow down. A second requirement of healthy
feet is proper farrier care. Having the feet trimmed on a regular schedule
by a qualified farrier will ensure that the hoof is kept balanced to
the horse's body, properly shaped according to his wear pattern. The
farrier also provides a second pair of objective eyes that will often
notice changes the owner misses. When problems arise, either from use,
age or disease, the farrier can work with the veterinarian to provide
trimming and shoeing therapies that may keep the horse more comfortable
and possibly extend his use. Finally, it is crucial that the owner exhibits
conscientious maintenance of the feet. This includes frequent cleaning
of the horse's feet, maintaining healthy living conditions and scheduling
the necessary professional care.
A strong foot is essential to the total health and usefulness of the
horse. Too much cannot be done to keep it in condition and performing
properly. Considering the size and weight of the animal it supports,
it is an amazing structure. Many of the lamenesses that arise from the
hoof are not necessarily a function of the foot's weakness, but of a
fault in the care it receives. When the owner provides the maintenance,
nutrition and farrier care the horse needs, keeping the feet healthy
and strong for a long, useful life is made easier.
