all around the Equine Hooves
One can acknowledge that from the time man has kept Horses, he has spent much time devising ways to protect their hooves. This article cannot possibly delve into the full complexities of this subject matter, but instead will attempt to point out the basics.
I would like to outline the use of two plastic materials (Trotters and Marathons) with which I have had some expierience; in addition to the classical shoeing with irons.
The basic principle of preparing the Hoof is the same regardles of the material. To start one needs to remove the old shoe. Following this one must trimm the Hoof, while at the same time developing a "line of attack" for the later steps. Naturally, an important point is one must take into account differences in weight distribution, which is diffused in more depth in Unshod
I file and prepare all the hooves according to their weight distribution by first shortening the bar to match the shape of the Sole, and then by cutting the Frog where necessary.
The latter is particulary important in prevent pockets developing in the Frog near the bulb of heel, or in straightening crooked frogs.
All loose horn on the sole needs to be removed, so one can see that the surface of the sole is as smooth as possible (without ridges or protrusions).
To conclude I rasp the unshod hoof in the direction of the toe. To determine how much to rasp off, one must concider the hoof profile (weight distribution) and the manner of the horse´s gait.
What always provides helpful clues is assessing the wear of the old shoes.
The majority of horses have the habit of walking on the outside of the hooves (like Charly Chaplin) even when appearently pigeon-toed. When one doesn´t follow this simple rule, you disturb the horses equilibrium and it has to "re-wear" it´s natural posture into the shoe, which places undue stress on the Hoof Tendons.
It also disturbs the horses gait. If shod properly, the movement is more fluid with the front hoof being able to lift better and the
front and hind legs not connecting with each-other.
Following this, one must cauterize very long as this can dry the hoof out, but instead hold the iron on the hoof just long enough to be able to ensure the nail hole impressions of the burnt on iron pattern cover the White Line.
One can obviously deduce that when using plastic shoes, one is unable to gererate a burn pattern on the hoof prior to shoeing. One must therefore meticulously ensure the shoe matches the entire hoof profile.
Marathons have an engraved plan on the other side indicating how the shoe must be orientated to the front.
Trotters are symmetrically even on the underside, where one can obviously locate the toe direction.
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Follwing this, the shoe is fixed with as few hob-nails as possible. If the nails are too large one stresses the wall of the Horn. By being over-elaborate on the nails, in particular at the back of the iron, one disturbs the Hoof-Mechanism.
To finish with finesse, one must cut the hob-nail, make a small indentation on the hoof under the nail and bend the end of the nail into this indentation. Then one must rasp off all the overhanging edges of the hoof and smooth the edge (Ground Border of the Wall), to prevent the horse from injuring itself on any unnessesary sharp edges. The methodology behind the plastic shoes is identical. For Irons I normaly use 6 hob-nails on the front and 4 at the back, while for plastics I use 4 at the front and back.
The newly shod Hafling.
Closer detail showing a shortened toe and 6 front nails. I always file the outside of the hob-nails, so the horse cannot injure itself on the sharp points and to ensure that if the horse throws the shoe (partially or completely), it doesn´t loose half the hoof with it (the bent nail frees itself easier from the hoof).

Preparation of the hoof for Trotters or Marathons by flat rasping.
Unfortunately with Trotters, one doesn´t have any inscribed nail positions, so one must symmetrically even out the weight bearing outer rim of the hoof by rasping it to ensure an even edge thickness.

This is to enable one to calculate back symmetrically to locate the optimal nail positions. The fact that it is impossible to see where one is driving the nail into the hoof, is a significant disadvantage of using these shoes. It is only with some experience, that one is able to fill this these shoes comfidently. The hoof shod with Trotters - the nails have still to be cut etc. Worth noting is the protruding rim over the plastic shoes, to enable the hoof to move freely on the shoe - see Hoof Mechanisms.
This horse actually stands very straight, which is unfortunately is not evident from the angle of the photo, where instead the toes appear to point outwards.
The shod Marathons, which in contrast to the Trotters have predetermined hob-nail hole positions inscribed. A further positive point is one sees the hoof profile through the transparent material.
Note, one again the overhang of plastic left bordering the edge of the hoof.