Page 1139 - Adams and Stashak's Lameness in Horses, 7th Edition

Foot Care and Farriery 1105

and delays break‐over on that side of the foot. When the margin. An extension such as a wide lateral heel branch in
branches of the shoe are fullered, the nail holes are a hind shoe is available as a manufactured shoe. A similar
VetBooks.ir and outside of the nail heads. A classic example of a forward or backward or by setting one branch of the
effect is obtained by using an oversized shoe fitted either
centered in the groove, which conforms with the inside
shoe wide.
shoe that uses two of these modifications is a half‐round,
half‐swedge shoe worn on the hindfeet by harness Every extension has the potential to cause the shoe to
horses. The inner branch is half round in cross‐sectional act as a lever. This lever action may be static, when the
profile and the lateral branch of the shoe is swedged. animal is not moving and the foot is bearing weight, or
Thus, the medial branch, enhanced by the half round, dynamic, particularly during the landing and break‐over
breaks over rapidly, whereas the break‐over of the lateral phases of the stride. When force is exerted on the exten­
branch is delayed by the swedge. sion by the ground, the forces are increased in the adja­
The only common modification to the solar surface cent wall and decreased in the opposite wall as the center
of the shoe is beveling of the inner half of the web of pressure of the GRF shifts. In addition to acting as
toward the inside with a hammer or a grinder, called levers, extensions increase the surface area available for
seating out or concaving. Horses with flat, thin soles ground contact, which decreases the amount of shoe
benefit from a seated‐out or concave shoe to decrease that descends into soft footing at that point in the cir­
pressure on the sole adjacent to the wall (Figure 11.18). cumference of the foot. The term floating or flotation
Safing decreases the likelihood of the shoe being stepped effect refers to the web width of a section of the shoe
on by another foot and pulled off. Boxing the heels that limits the amount of this part of the shoe that
allows the farrier to fit the shoes with more expansion descends into soft footing (Figure 11.22).
(width) at the heels without a ledge being present, Lateral or medial extensions may be used to force the
which can easily be stepped on by another foot. opposite wall of the hoof capsule to the ground or sup­
Clips are triangular‐shaped projections that extend port the wall adjacent to the extension. In doing so, the
proximally from the periphery of the shoe (Figure 11.21). lever decreases the compression in the opposite wall and
Clips are preformed on manufactured shoes or they increases the compression in the side of the hoof on
may be forged in the shoe at the time of fitting. When a which the extension is being used. Heel extensions fre­
shoe is fitted, the outer surface of the clip is congruent quently are used on one side of the foot or biaxially
with the surface of the hoof wall. Movement between (Figure 11.23). When used in performance horses, exten­
the shoe and the hoof capsule is reduced, which decreases sions are continuations of the heel of the shoe and are
the shear stress on the hoof nails. A single clip placed called trailers.
in the center of the toe or side clips placed at the toe Trailers are used almost exclusively on the lateral
quarters can be used on front shoes, while side clips branch of hind shoes. Egg‐bar shoes that extend palmar/
placed at the toe quarters or quarters are generally used plantar to the heels of the hoof capsule act as heel exten­
on the hind shoes. Clips may be positioned elsewhere sions. They are most commonly used on the front feet
around the periphery of the shoe when additional stabi­ but can also be used on the hindfeet when necessary.
lity of the hoof capsule is necessary. Force applied on the butt of an egg‐bar shoe decreases
the moment about the DIP joint and the tension in the
Extensions DDFT. Therefore, horses convalescing from a DDFT
injury may benefit from heel extensions used in conjunc­
An extension on a horseshoe is any projection of the tion with some type of heel elevation. The egg‐bar shoe
shoe that extends outward beyond the perimeter of the acts as a palmar extension, and when the horse is on a
foot in the horizontal plane. Extensions may be placed soft surface, it reduces the sinking of the heels into the
anywhere around the circumference of the foot. They surface at the beginning of the stride and acts as a heel
may be forged into a shoe or welded onto the outside wedge during the support phase of the stride. On the
5

A B

Figure 11.21. A steel hind shoe with quarter clips (A) and a clipped steel hind shoe fitted to the foot (B).