The Rudiments of the Farrier's Art
by Dave Millwater, RMF
Hoof balance. It's an almost mystical term used by farriers. Establishing it is perhaps the most essential aspect of the horseshoer's art. Many horse owners don't fully understand what hoof balance is. But they know that if their horses don't have it, they may suffer from poor movement, interference, or lameness. Many good farriers don't seem to consciously know the technical features of hoof balance, but instead have developed a subconscious understanding of it through years of experience. This works fine for them when shoeing a horse, but doesn't allow them to explain balance to the owners.
Hoof balance is four dimensional geometry. The three spatial dimensions; usually defined as height, width, and depth are pretty obvious. The fourth dimension is Time, which manifests as movement, growth, and change. It's this fourth dimension that makes things tricky. Were it not for this dimension, anyone with good measuring tools and the ability to read them could ascertain balance.
The most commonly measured aspect of hoof balance is toe angle. Viewed from the side, the toe angle is made by the dorsal surface and the solar plane of the hoof.
Somewhere along the line, long before the hoof protractor was invented, some fellow who probably never shod horses decided that 45 degrees was the proper toe angle for front hooves. This erroneous idea has been passed down in books from around 1800 to the present. Such a low angle is out of balance for most all horses.
It transfers an excessive amount of loading to the heels, increases the stress on the Deep Digital Flexor Tendon (which uses the navicular bone as a pulley), exposes the navicular to direct trauma, and delays the breakover of the hoof which can lead to forging or overreaching.
Viewed from the side with the horse standing square, the slope of the pastern changes inversely to the slope of the hoof (toe angle). When the hoof-pastern axis appears straight or just slightly broken forward (i.e. the hoof looks slightly more upright than the pastern), the toe angle may be considered acceptable.
Many farriers consider the shoulder angle when determining the toe angle for the fore hooves. This can be indeed be useful. Although the hoof need not necessarily be at the same angle as the shoulder, a relatively steep or low shoulder angle may indicate a correspondingly steep or low hoof angle.
The methods of establishing the correct toe angle usually apply to the fore hooves. The hinds are commonly the same as the fores, or slightly more upright.
But we have yet to factor in Time. The hoof wall grows fastest where it bears the least weight. Increasing the hoof angle shifts weight from the heels to the toe, decreasing it has the opposite effect. This means that (barring internal damage) a toe angle that decreases over the normal shoeing period was probably set too low to begin with. A toe angle that gets steeper was probably set too high at the onset. This growth pattern can be used by the farrier to fine tune the toe angle balance.
An aspect of hoof balance related to toe angle is the slope of the heels. Viewed from the side, the heel slope should be about the same as the toe. If the heels are more upright than the toe, you are dealing with a club foot. If the heels are more than about five degrees shallower than the toe, they are said to be underrun. Heels need not be short to be underrun. Both conditions require special attention from a skilled farrier.
Ideally, the hoof's base of support should extend back to a line continued down from the center of the cannon bone to the ground. If the hoof does not extend that far back, the heels of the shoe should.
The balance of the inner and outer halves of the foot is called mediolateral balance. Mediolateral imbalance in the hoof causes uneven stress distribution to the sensitive structures within it, and strains joints in the leg. Horses with out of balance hooves are also subject to faults of gait and stance.
Probably the most common way farriers are taught to judge mediolateral balance is to "look down the leg". This means to lift the foot as though you are going to pick it out, then hold the leg just below the knee or hock, letting the hoof and fetlock hang loose. Using this method, the hoof is considered to be in mediolateral balance when its solar plane is perpendicular to a line continued from the center of the cannon.
Many farriers choose to take the fourth dimensional aspect into account when establishing mediolateral balance. They usually do this by watching the horse move and observing whether one side of the hoof lands before the other.
Another, and perhaps the most comprehensive, method of judging mediolateral balance is by observing the worn horseshoes. This method has the advantage over "looking down the leg" because the shoe will respond to stresses caused by conformation flaws and other features that might deceive or be undetectable to the eye. The worn shoe gives more information than watching the hoof land because the shoe wear shows which side of the hoof was more heavily loaded rather than just which side landed first. The shoe also records data about the loading pattern of the hoof over the entire shoeing period... Longer if the shoe is reset.
Many books intended for horseowners state that the outside of the hoof wall should never be rasped for fear of removing the periople. The truth is that the periople rarely extends more than an inch down from the hairline. The very thin stratum tectorium varnish that does sometimes extend the length of the wall is not so important that it justifies ignoring flares. It is often necessary for the farrier to use the rasp to sculpt the hoof wall back into some semblance of symmetry. The stratum tectorium can then be replaced with a hoof sealant.
A hoof made asymmetric by flares in the wall will be functionally out of balance. Toe flares have the effect of decreasing the toe angle. Flares on the sides of the hoof have the effect of throwing off the mediolateral balance. Flares are distortions of the hoof wall; and hoof horn, like all other materials, has a limit of how much distortion can be tolerated before fracture occurs. If hoof wall flares are left unattended they can not only cause the problems associated with imbalance, but hoof cracks as well.
The habits of some incompetent horseshoers who fit shoes poorly then dub off whatever hoof hangs over has prompted the axiom: "Fit the shoe to the hoof, not the hoof to the shoe". This saying has lead some people to think the shoe should accommodate the shape of the foot no matter how distorted that shape is. The farrier's real job is to put the shoe where the base of support belongs, whether that is where the hoof originally was or not. That is the art of horseshoeing; what balance is all about.
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