The horse owner's guide to shoeing & trimming horses.

Part II

Another interesting point related to angle and your farrier's tools has to do with the wooden handle on the rasp. Some horse owners have a rasp to trim up their horse's feet between visits from the farrier, to keep the feet from chipping up. This often results in the horse's heels and angle being lowered too much. Why? It is natural when using a rasp which has a handle on it, to push downward on the handle more than you push forward, because your hand and weight are above the handle and not behind it. When you start to rasp at the heels and push toward the toe, you unknowingly push down on the heels and remove more hoofwall from the heels than from the rest of the foot. Your farrier is aware of this, but most horse owners are not. In some horseshoeing schools, the students are not allowed to use a handle on the rasp when they are learning how to trim.

Although horseshoes do not change a horse's angle, there are special wedged pads (thin at the toe and very thick at the heel), and handmade shoes with wedge shaped lifts, which can raise a horse's angle artificially. If a horse's feet have been worn down severely as a result of riding on hard surfaces without shoes, then it may be impossible for your farrier to make any adjustments in the angle, because there is simply no excess hoofwall to trim. When it is not possible to adjust the angle by trimming, it is possible to adjust the angle by using wedged pads. This would only be recommended if the horse were actually lame due to extremely low angles, however, because simply shoeing the horse will allow the hoofwall to grow out and be trimmed to the proper angle when the shoes are reset.

It is probably impractical to use wedged pads on feet that are excessively worn anyway. When the feet become badly worn, it is difficult to fit shoes so that they will stay on, and pads would only increase the likelihood of the shoes becoming loose.

To balance your horse's feet, the farrier can only remove excess, or extra, growth from the hoofwall, and discarded, or shed, sole. When the wall and sole can't be removed to a degree that balances the foot, more correction has to be made the next time that the horse is trimmed or shod. When the hoof is excessively worn down, not much can be done in one trimming; and when the hoof is so long that the hoofwall has bent, or flared, it may take two or three trims to bring the foot back to normal. The point is not that horse's feet need to be trimmed on a regular basis, which they do, but that if you have neglected your horse's feet for several months, then you can't expect your farrier to correct your horse's balance in half an hour.

In an age where we have come to expect that our needs will be gratified instantly, many people expect an instant solution to their horse's hoof or balance problems. It is very satisfying to the farrier and the horse owner when problems can be corrected in one trimming, but it is also very unusual. Some farriers offer instant solutions, and some horse owners are impressed by, or talked into, them; usually at great expense to the horse owner. These instant solutions are passed off on the horse owner as corrective shoes, the most common being shoes with trailers, shoes with lifts, ridiculously expensive space-age plastic shoes, and bar shoes.

Trailers, or extensions on the heel of a horseshoe which stick out to one side slightly, are in all cases dangerous to the health of your horse's legs. A horse with toed-in feet, for example, is sometimes shoed with trailers on the outside of the shoe as an instant solution to the problem. The hoofs will gradually straighten themselves out when they are balanced, but the trailers will violently twist and jerk the hoof and pastern joint to the outside, each time that the hoof is set down. This is caused by the trailer, or extension, contacting the ground first, causing the foot to pivot on the trailer. Lameness and permanent damage can result from this extreme correcting. Trailers do work, however, which is why they are commonly used on racehorses.

Sometimes trailers are sold to horse owners as an instant cure for cow-hocked horses, horses whose hind feet are pointed outward, with the hocks being closer together than normal. Cow-hocks are a conformation fault, not a balance or hoof problem. The condition is termed a conformation fault because it is the fault of how the horse has been put together by God and genetics. Some horses are just destined to be born with the ball and socket positioned on the pelvis in the wrong place, causing the hocks to angle in and the feet to angle out. By no stretch of the imagination can this condition be corrected by shoeing or trimming. It is possible to twist the hoof and joints straight, but this is at the expense of placing unusual strain on the joint, ligaments, and muscles, while leaving the hocks close together. The hoofs are literally twisted, not corrected. A cow-hocked horse can give you a lifetime of pleasure riding without correction. The outside of the hoofwall will contact the ground first when the foot is set down, however, causing the hoof to wear unevenly. This is a problem if you ride frequently or on hard surfaces, but can be solved with normal shoeing.

Cow-hocks are a result of improper breeding, not improper trimming or shoeing, and can only be prevented by good breeding.

Handmade shoes with wedged heels are commonly sold as an instant solution for raising a horse's angle. If a veterinarian has diagnosed your horse as having navicular disease, then it is very desirable to instantly raise the angle, but if the angle is low from improper trimming or lack of trimming, then the problem can be corrected in two or three trims; without the added expense of handmade shoes. Besides, wedged shoes only work on hard ground. On soft ground the wedges sink in leaving the horse with the same angle he started with.

Plastic shoes transmit much less concussion to the hoof than metal, and are lighter. They cost much more than metal shoes and cannot be shaped like metal. When they will fit your horse's feet they can be very useful on horses that are gamed or worked very hard, and can help horses with concussion related lameness. Some plastic shoes are sold as therapeutic shoes with a built-in wedge that contacts the frog. The purpose is to exercise a frog which has atrophied from lack of exercise, or which has been destroyed by thrush. When the frog is exercised it expands, which also expands the heels. Therapeutic shoes are also sold as a cure for contracted heels since the expansion of the frog expands the heels, returning contracted heels to their normal position. The shoes are also misrepresented by some farriers as a cure for foundered horses.

As you can figure out for yourself, however, a frog that has atrophied from lack of exercise can be restored to its normal condition through normal exercise without corrective shoes. Likewise, a frog that has been destroyed by thrush will recover on its own once the thrush is cleared up. The cure for these two problems is really just normal exercise. Contracted heels also cure themselves once the frog is healthy enough to expand the heels, although a plastic shoe with a frog wedge will remedy this condition quicker than exercise alone; the question is whether the expense is justified.

Foundered horses are sometimes treated with a handmade shoe which puts pressure on the frog, restoring the coffin bone to its proper position inside the hoof. The position of the coffin bone, however must be precise, and determined by a radiograph which is read by someone trained to read the pictures. This process cannot possibly be accomplished with a plastic shoe having a non-adjustable frog support. To use this shoe on a horse that is in the acute stage of founder is very questionable. To use this shoe after the

disease has run it's course, and the coffin bone is reattached, is pointless.

One further problem with plastic shoes, which never seems to be mentioned, is that the shape of the shoe is adjustable only to a very small degree. This results in the horse's hoof being shaped so that it will fit the shoe. One of the primary principles of shoeing horses is that the shoe should be shaped to fit the hoof, not the opposite.

Bar shoes; also egg-bar shoes. These shoes have achieved some sort of mythical status as a miracle cure for contracted heels, although some farriers also use them for foundered horses and horses with undershot heels. The shoes were designed as a corrective shoe for contracted heels, the theory being that if the shoe is a one-piece oval or round shape without the normal empty space between the heels, then the horse's hoof can no longer contract because the shoe keeps the heels spread apart. This is quite a leap of logic. First, this theory assumes that a horse's heels are capable of actually pulling the heels of a normal horseshoe together, so that a bar must be placed between heels to prevent this from happening.

It requires a hammer, a strong arm, and an anvil to bend the heels of a horseshoe; using a solid steel bar to prevent the heels from pulling in is just, pardon my French, stupid.

The most amazing logical folly in the bar shoe theory is that while the purpose of the shoe is to keep the heels from contracting, the heels of the hoof are never nailed to the shoe. No nails are ever driven in the heel area of the hoof; you will notice that the nails always stop just before the heels on any shod horse you look at, including horses with bar shoes. If the horse's heels aren't even connected to the shoe, what possible good can the shoe do? Some proponents of the bar shoe believe that the bar puts pressure on the heels to make them expand normally. The actual bar portion of the shoe doesn't touch any part of the hoof, however, and what pressure is supposedly provided that isn't provided by the hoof simply stepping on the ground instead of on the shoe?

Bar shoes serve no purpose for foundered horses, I have never read any material that suggests that they do. You may not have seen a horse with undershot hoofs. The condition occurs when the heel portion of the hoofwall has very little angle and shoots too far forward before making contact with the ground. It looks like the horse's hoof is too far in front of the leg, which it is. This problem is the result of letting the horse go for long periods without trimming, or from continuously trimming the horse improperly, so that the angle is too low. Normally your horse's weight is evenly distributed over the entire hoof. When the weight is shifted back on the heels because of a low angle or long feet, then the material of the hoof wall actually starts to bend from the pressure exerted by the weight of the horse's body. In extreme cases the heels actually look crumpled up, and the folds in the hoof wall are obvious. In mild cases the hoof is forced to grow more forward than downward at the heels. The condition is correctable by restoring the balance to the foot through timely, repeated trimming. The bar on the shoe takes the place of the hoof, providing support in a position where the hoof, if it were normal, would be providing support. This eases the strain on muscles and tendons and prevents the hoof from rocking backwards, but it does not relieve the pressure on the heels. The pressure can only be relieved by balancing the hoof.

Don't get the impression that your farrier is trying to rip you off by selling you corrective shoes. Corrective shoes have been passed down generation through generation and there is more than a little folklore and mystique associated with them; the vast majority of the farriers who use them truly believe in them. Also remember that most of these shoes are used on money-making horses, racing and show horses that provide the livelihood for their owners. Such owners are more likely to want instant solutions to hoof problems, or to try any solution that will keep their horse producing money. The owners of pleasure horses have the wonderful luxury of time, of being able to do what is best for their horse's health through proper trimming and allowing the feet to slowly and naturally correct themselves.

Toe length is a term that many horse owners have heard and understand, but believe to be something separate from angle. Toe length is measure bottom of the coronary band to the tip of the toe at a place that exactly divides the hoof into two equal halves. What confuses most people is that toe length increases or decreases as the angle and amount of foot touching the ground increases or decreases. Toe length is the end result of how much foot is on the ground, not of how the front of the hoof is trimmed. As the heels are lowered and the angle of the hoof decreases, more hoof is in contact with the ground (the surface area is increased). This is like slicing salami or bologna for a coldcut tray, and slicing it on an angle instead of straight up and down. The less of an angle you slice the coldcuts at, the bigger the slices become. As you decrease the angle you increase the amount of surface area. In fact, you may have noticed that when the angle of your horse's feet is lowered, a larger size shoe is needed to cover the hoof, and when the angle is increased, a smaller shoe is needed.

Toe length can be artificially shortened by squaring, blunting, or rounding off the toe, but that is not what is meant by toe length. The importance of toe length as a means of balancing your horse's gait and achieving smooth movement, is in how much foot is touching the ground, which determines how much time it takes your horse to get its feet off of the ground.

Friction and a resistance to being moved from the ground increases as the amount of foot on the ground increases. This is important because if one front foot, for example, has a longer toe length than the other, it will be lifted off of the ground later than the other. This causes your horse to be slightly out of step and awkward. This also causes a higher arc at the end of the stride on the longer foot, causing this foot to come down harder than the other foot. This is a difference which might possibly be felt by the rider.

Two different people can measure toe length and come up with slightly different measurements because exactly where the coronary band ends is not precisely clear. It doesn't really matter, though, because the important thing is that both front feet are the same length and both hind feet are the same length. The measurement itself is only important for breed shows where a maximum toe length is specified.

Rasping back the toe so that it looks squared, rounded, or rolled is technically different from adjusting the toe length even though the effect is the same as shortening the toe length. When the toe is squared off most farriers refer t this as decreasing the breakover time. Breakover is that point in time when the horse's foot rotates forward and passes over, rolls over, or more properly, breaks over the point of the toe. When you decrease the breakover time and create a quicker breakover, the foot gets off the ground quicker, which can solve some interference and stumbling problems. Most often, your farrier will square off the toe when you complain about your horse stumbling.

Not all stumbling and tripping problems are cured by cutting back the toe to quicken the breakover, so your farrier may not be at fault if your horse still trips after having his toes squared. Some common sense is required with horses who trip or stumble. Young horses have to learn to balance themselves with a rider on top of them; when they trip it is usually just a lack of coordination. Riding your horse over broken fields can easily cause tripping and stumbling, especially if the horse is accustomed to riding on the road or in an arena where the surface is level. Very soft ground and mud make any horse stumble, some more than others depending on the horse's weight and the rider's weight (the heavier the horse, the further he sinks into the mud). And, yes, even though we may not admit it, some horses are simply fat, out of shape, or just plain lazy. Stumbling can decrease without squaring the toe by letting your horse grow accustomed to different terrain, building up muscle tone, and improving coordination. Once you have decided that there is no logical reason for tripping, then ask your farrier about squaring back the toes.

Reducing the breakover time also reduces the strain on the flexor tendon and the pressure on the coffin bone, so your veterinarian may recommend squaring the toe to aid in treating several medical problems. If your horse is nosed as having navicular disease, the toe may be squared and the heel raised, increasing the angle. If your horse is diagnosed as having laminitis (founder), however, the toe may be squared while the heels are lowered. This is to shift the weight back, off of the front of the coffin bone.

Once your horse's feet are balanced and symmetrical, your farrier can fit shoes to the hoofs if they are necessary. Unshod, or barefoot, horses will have the outside edge rasped, or rounded, off. This helps prevent chipping and splitting. The edge is left on a horse to be shod so that the hoof wall will fit flush to the shoe.

Some farriers object to anyone saying that they |nail on' horseshoes, because this make a very exacting art sound like boarding up a window. Not only does |nailing on a shoe' not do justice to a farrier's skill, but it sounds destructive and harmful. To an extent, it is destructive and harmful.

Nailing shoes on your horse's feet is the lesser of two evils. A small amount of damage is done to the hoofwall to prevent a large amount of damage from being done. Shoes prevent cracks, chips, and excessive wear from damaging the hoofwall. Shoes do not prevent the sole from being damaged by rocks unless a pad is placed between the shoe and the sole. It is a common misconception that the shoe will prevent damage to the sole by raising the hoof off of the ground. The amount that the hoof is raised by the shoe is hardly enough to allow your horse to walk on rocks without touching them. The sole, in most circumstances, is protected by it's own hardness and thickness.

Back to the lesser evil. What damage is done by the shoe, anyway? Very little. It is the nails that do the damage by splitting apart the fibers of the hoofwall. The hoofwall cannot repair itself, the fibers remain split until they grow out and the damaged wall is nipped off. This is not a real problem unless the hoof is very dry and several sets of nail holes (from repeatedly resetting the shoes) cause the lower wall to crumble and break up. The most common cause of this problem is just a lack of moisture in the hoofwall, which can easily be corrected by using a hoof moisturizer, providing a wet area for your horse to stand or exercise, or possibly just allowing the horse to get outside more often if the horse is in a dry stall with absorbent bedding most of the day.

The horseshoe nails also tend to split up the hoofwall on horses which have a dietary deficiency, or horses who may be too old to get the most out of their feed. In these cases a vitamin or dietary supplement may restore the hoofs to normal. Also, if your horse is standing in urine soaked bedding or ground continuously, the hoofwall becomes soft and spongy at the bottom; the ground surface of the wall will look like it's fraying and falling apart. It is; and when horseshoe nails are driven into a hoof like this they can tear right down through the hoofwall, making the wall even worse.

When the hoofwall is kept pliable by muddy ground, water, dew on the grass, hoof moisturizers, and proper diet, then shoeing your horse will not cause any meaningful damage.

Other than lack of moisture, the major cause of hoofwall breakup is the size of the horseshoe nail. The standard horseshoe nail for pleasure horses is much thicker and broader than a racehorse nail of the same length. The main reason for this is not only tradition, but also because the thicker nails have a large head which fits the nail crease of the most commonly used American horseshoe. This is too bad, because the thick nails cause much more damage than is necessary. The widespread use of the thicker nail has lead to the common practice of using only six nails to nail on a shoe, because this reduces the amount of overall damage. In fact, if you watch a horse being shoed with the thicker nails, you can usually see a split above and below the nail, sometimes even an oval shaped opening is visible around the nail.

Thinner nails not only cause less damage when they are driven through the hoofwall, but also do less damage to the hoofwall when a horse throws a shoe. Thinner nails are now manufactured to fit the nail crease on standard American shoes, so there is no longer any reason to use the thicker nails.

Using only six nails per shoe has become a very strong belief with many horse owners. Just remember that seven or eight thin nails do less damage than six thick nails, however, and that having a shoe fall off usually does much more damage than any amount of nails can do. In addition to this, larger feet require larger shoes, and very often, more nails to hold the shoes on.

Although the nails, not the shoes, are the potential danger to your horse's feet, the horseshoes do have liability - weight. Any increased weight that your horse has to lift increases fatigue and decreases agility. You may laugh at this idea because a horse is such a big animal. How could four little shoes affect the horse at all?

You and I can certainly notice the difference between wearing no shoes and wearing sneakers, work boots, or barn boots. When we have to walk or run any distance, even a little extra weight takes it's toll on our muscles and energy. Consider this; you go for a one mile ride with your horse. If your horse moves forward six feet every time all four feet are moved, then each foot is lifted 880 times during the ride (5,280 feet in a mile). On a longer ride, your horse may lift it's feet thousands of times, lifting thousands of pounds of horseshoes if a set of four shoes weighs one pound.

Certainly your horse becomes conditioned to lift the extra weight of horse-shoes, just like any athlete becomes conditioned to lifting weight, but the important point is that when your horse does need shoes, they should be the lightest shoes that will do the job of protecting the hoofwall. Using heavy shoes, just so the shoes will take longer to wear out, and you will spend less money on shoes, is not fair to your horse. Aside from increasing fatigue, heavy shoes cause more concussion to be transmitted to the horse's feet. Not all of the concussion caused by the horse's feet striking the ground is absorbed by the ground. The harder the ground surface is, the more concussion is transmitted back up the horse's hoof and leg. Over a period of time, the concussion can take a toll on your horse's feet.

Not only do some horse owners use heavy shoes so that the shoes will wear longer, but some owners also use high alloy, or hard steel shoes so that the shoes will wear longer. High alloy shoes resist wear, but also cause more concussion to be transmitted to your horse's feet than low alloy, or soft steel, shoes. If you take a high alloy shoe and drop it on concrete, the shoe will ring and bounce; if you drop a low alloy shoe it will clunk and bounce much less. The softer shoe deadens vibration and reduces concussion even though the two types of shoes may weigh the same. This may not seem to be very important, but if your horse is going to spend years pounding it's feet on hard surfaces (which is usually why you need shoes in the first place) then every little thing that you can do to reduce concussion will prolong your horse's useful life.

Low alloy shoes also have the added advantage of slipping less on asphalt than high alloy shoes do. The asphalt |bites' into the shoe so that scratches and wear on the shoe are obvious. High alloy shoes resist the abrasion of the asphalt, and slide instead of biting in. Of course this means that the low alloy shoes will wear out quicker and you will be spending more money on shoes. The money, you would save by using high alloy shoes, however, is usually offset by having to pay for borium on the shoes because they slip so much. The softer shoes don't need to be treated with borium.

Rimmed shoes (as opposed to flat shoes, which are completely flat on the ground surface, except for the crease where the nails sit) also decrease slipping on hard surfaces, because there is less shoe surface in contact with the asphalt, and the sharp edges of the rims tend to bite into whatever surface the horse is on.

Just to make things confusing, you should know that eliminating all slip or slide when your horse's feet contact the ground would be bad for your horse's legs. Imagine yourself jumping forward on a concrete or wooden or linoleum floor. If you were wearing sneakers and your feet did not slide at all on the floor, you would feel considerable strain right up to your knees; you might even hurt yourself. If you were wearing shoes that allowed you to slide a little, without slipping and falling down, the strain to your legs would be tremendously reduced. The same is true with your horse's legs.

While borium, which is widely used on horse's shoes, stops horse's feet from slipping on pavement, it also brings the horse's feet to a very sudden and complete stop (depending on the amount of borium). Your horse's feet are designed to slip just a little when they come down, to reduce strain on the leg. Your horse's feet are not designed to ride on pavement, no matter how hard we try to make them adapt. When we try to change the design that thousands of years of evolution has determined is the best way for a horse's feet to function (sliding on contact with the ground), then we have to be prepared for lameness and a shorter working life for the horse. If we try to change where horses are intended to walk, trot, and run, by taking them out of the field and putting them on the road, and still allow the feet to slide naturally, then we have to be prepared to have the horse slip and possibly fall. While a happy medium may be possible using low alloy shoes, it is not the horse's fault when they slip on the road, and it is not necessarily the farrier's duty to stop the horse from slipping. Horses just weren't designed to ride on the road.

One other interesting part of using borium is that if the borium is applied unevenly to the shoe, the horse's balance can be thrown off side to side, and the horse's angle can be changed in either direction.

As a result of the natural sliding motion of your horse's feet, no matter what surface you are riding on, the horse's shoes can become loose. Over a period of time the slight forward motion each time that the foot is set down will rock the nails back and forth just enough that they can eventually loosen. This is not normally a problem when the shoes are reset every six to eight weeks. Some farriers may use a toe clip (either making one by first heating the shoe and then drawing out a clip, or by using a shoe with a factory clip) to prevent the foot sliding forward on the shoe. The toe clip is hammered tightly against the hoof after the shoe has been nailed on.

When your farrier uses a toe clip, a space has to be made at the toe for the toe clip to fit into. The farrier will either cut out a spot with the hoof knife, nip one with the nippers, or file one with the rasp. If the shoe were put on without making a spot for the toe clip to fit into, then the clip would prevent the toe of the shoe from being under the toe of the hoof, and the shoe would stick out in front of the hoof, making the hoof longer and the angle lower. This would obviously change your horse's balance.

Less common than toe clips are side clips. Side clips are placed one on each side of the hoof, but towards the front of the hoof to prevent sliding from side to side as well as forward.

You may know people who have their horses shoed on the front feet only. This is a fairly common practice for three reasons. Horses carry the majority of their weight, and the majority of your weight, on their front feet. This alone results in more wear on the front feet than on the hind. You may ride often enough that the front feet would wear down too much without shoes on, while the hind feet are able to keep up with the wear they receive.

Secondly, horses running together in the pasture or paddock occasionally (or frequently, depending on the horses) kick each other. A horse with shoes on the hind feet is capable of inflicting serious damage to another horse, much more damage than if left barefoot.

Also, if you trail ride, sooner or later someone's horse will kick out at another horse and unintentionally kick the rider instead of the horse. The difference between bare hind feet and shoes can be the difference between a bruised leg and a broken leg for the unfortunate rider.

There are two fairly popular misconceptions conceptions about horseshoes that are worth mentioning. One is that a wider horseshoe will bear more weight and thus help horses with hoof injuries, or just be easier on your horse's feet. It is possible for a very wide shoe to protect and actually support the sole of a foundered horse, but then so do pads; and a pad will protect the entire sole, not just part of it.

All of your horse's weight is certainly on the horseshoes, but the only weight any shoe (wide or narrow) distributes is the amount of weight that is being put on the ground, in pounds per square inch. A wide shoe puts fewer pounds per square inch on the ground surface than a narrow shoe. This is the same principle as snowshoes; but the only thing that bears your horse's weight is the hoofwall. Just because your horse's weight is on the shoe does not mean that the shoe is bearing your horse's weight. The hoofwall is still bearing or supporting the weight of your horse even when the horse is shoed. The shoe is simply placed between the ground and the hoof. Remember, horse's feet are constructed differently than ours because the last bone in the leg, and therefore the bone column of the leg, and the weight of the horse, is suspended inside the horse's hoofwall. The bone is not placed on the ground like the bones of our feet.

All of the horse's weight is supported by a hoofwall that is only an average of three-eighths of an inch thick; and the only thing the shoe actually needs to cover to prevent wear is this narrow piece of wall. Nailing a shoe to your horse's foot cannot make the shoe a part of the horse's physiology, and the whole concept of wide shoes bearing more weight is simply not based on fact.

The other misconception among some horse owners is that different breeds of horses need to be shoed differently than other breeds. Horses may need to be shoed in a certain way because of what the owner is doing with the horse (like racing, for instance), but not because of the breed of the horse. All horse's feet are constructed the same way, but come in many shapes and sizes. There are certain shapes of feet that are normally associated with one breed, but no breed is limited to one particular shape. Most importantly, the shape of the hoof has nothing to do with how your farrier trims or shoes the hoof, except that the shoe is shaped to fit the hoof. Some breeds have angle and toe length requirements for showing, but these are man-made rules.

The other misconception is that the shoe must always fit the hoof, no matter what. It is one of your farrier's main objectives to make the shoe fit the hoof, but sometimes the hoof will be unsymmetrical, or missing a large chunk, to an extent that the foot would start turning inward or outward if the shoe fit the hoof exactly. In this case the shoe can be shaped to look like what the hoof would normally look like if it were not damaged or out of shape.

Usually the first question someone asks when I start working on a foot is how much of the frog should be trimmed. Some horse owners have heard that none of the frog should be trimmed, some that most of it should be trimmed off, and some think that the frog should look |pretty' according to their own artistic standards.

For the frog to fulfill it's purpose of expanding the heels by flexing the rear of the hoof, and providing traction and a non-slip surface, the frog obviously has to touch the ground. To accomplish this the frog shouldn't be trimmed so low that it no longer touches the ground (regardless of whether the horse is shoed or barefoot). If the frog is higher than it needs to be the ground is just going to scrape, tear, or deform it until the frog is even with the bottom of the hoofwall. So one of your farrier's main concerns in trimming the frog is to trim it even with the bottom of the hoofwall or the bottom of the shoe.

The frog, when healthy, grows over into the grooves on the sides of the frog. This overgrowth is floppy, is not of any use to the hoof, and traps manure, dirt, and stones. The manure and dirt can create conditions where thrush can occur, and stones can obviously injure the sole. For these reasons all the excess frog needs to be trimmed off.

Torn or ragged pieces of the frog need to be trimmed off, not only because they are not useful, but mainly because they can provide nooks and crevices blocked off from the air where thrush can start. Also, in moist conditions, when the frog has gone a long time without being trimmed, the surface of the frog may become crumbly and flaky. This material needs to be trimmed off as it is no longer a functioning part of the frog.

Keeping the frog trimmed up helps make the commissure somewhat self cleaning. Most materials won't become lodged in the grooves to begin with, and the additional flexing of the frog causes debris to fall out of the hoof when your horse exercises. All of this is important because thrush needs a place where the bacteria is not exposed to oxygen. Anything that damages the frog or it's surface, or permanently traps materials in the commissures, creates places where the air cannot reach and where the thrush can live.

Trimming the frog is really quite simple, and while most of what your farrier does may look simple, there are dozens of things your farrier is looking at and thinking about to keep the feet balanced and your horse healthy and useful. Having a farrier examine and trim your horse's feet, even when there is not much physical work to do, is the cheapest insurance you can buy to prevent lameness, maintain good balance and an enjoyable ride, and detect problems in their early stages.

I hope this guide answered some of the questions you may have had about trimming and shoeing horses.