Certain ideal shape/form of the hoof is so called “regular hoof”, which has several basic concepts. The angle of the front wall of the hoof forms with the ground about 50’ by the front legs and about 55’ by the hind legs. From the profile, the heel edges are parallel with the front wall and in the front legs shorter by two-thirds than the toe wall. (see picture 1-A) By the hind legs the edges of the heel wall are about a half-length of the toe wall. (see picture 1-B)The angle, that the hoof wall forms with the ground in the widest part of the hoof is on the inside and outside about the same, 80 to 85 degrees. (see picture 1 -C)
The sole of the front legs are more or less round shaped, while by the hind is oval (elliptic). The proportions of the inside half of the foot with the outside is about the same. (see picture 1- A1 and B1)
This regular/correct shape of a hoof is very precious and is often connected to equally precious “regular stand” (correct conformation), which is not as common in horses as one would wish. The correct “regular stand” of the legs is such, that from the front they run parallel to the ground and the distance between them is as wide as the width of hoof in the same size. (see picture 2)
From the profile the limb hangs/stands straight down to the ankle and then slants to the ground in approximate angle with the ground of 50 to 55 degrees. (see picture 2)
Any kind of deviation of the regular stand will influence the shape of the hoof. The centerline passing through the foot is essential to the shape of the hoof. If the centerline of the hoof deviates towards the other leg inwards, such stand is called toed in, often called “pigeon toe”. If the centerline pointes away from the other leg outward, such stand is called toed out. If from the profile, the center line of the hoof forms with the ground the angle of more than 60 degrees it is accompanied with a high angled foot (not necessarily “club foot”), if the angle is less than 50 degrees it is accompanied with a sharp angled foot. (see picture 3)
While the regular foot equally distributes the stress/weight on the hoof wall around the outside carrier perimeter, in the case of the irregular foot the stress is uneven. In the case of the toed in foot, the greater weight is on the outer half of the hoof, and by the toed out foot it is on the inner half. In the case of the sharp angled foot, the heel is more weighed down, while in the high angled foot the toe is more stressed (does not apply when in motion). Due to the uneven weight distribution, certain parts of the hoof are more stressed than others, which often result in various lameness and unsoundness. For example a “quarter crack” can be often found on the outside by the toed in feet and on the inside on the toed out feet, often accompanied with high angled foot. The hoof cartilage by the older horse will calcify by the toed in foot on the outside, while by the toed out foot on the inside.
Naturally, due to the uneven pressure/impact of the irregular foot the shoes will wear off unevenly. This may be partially reduced with proper shoeing adjustments. There are often used special shoes for shoeing of the irregular hoofs. In the case of the sharp angled foot it is best to use a simple light plate of even thickness (no wedges!) and somewhat longer than in the case of regular foot. The high angled foot is best served with a shorter shoe. For the toed in foot is best to use a shoe with one end wider, sometimes turned out (hind legs). For the toed out horse the turned out end of the shoe seems practical. (the latter two are used mainly on draft horses, see picture 4).
This all is of course based on many years of experience of the farrier in the filed of irregularities and it solely rest on his decision which shoe should be used.