Written By Walt Friedrich
Things I’ve Always Wanted to Know about Horses’ Hooves but Didn’t Know How to Ask
This entry was posted on September 7, 2012.
If that fits you, then you’re in good company. Everyone with a horse or two has either been there or is there with you, right now – or soon will be. And it’s a conundrum. A hoof looks so simple; except for color, they all look very much alike. It’s so easy to take them for granted. But there are some questions:
How come some people have the guy come over every month or so and change the shoes? And how about hooves that don’t have shoes on, what’s up with that? Sometimes, instead of a shoe guy visiting regularly, there’s a guy with nippers and a rasp that comes around and delivers four pedicures on every horse. Both the shoe guy and the rasp guy look like they’re doing really intense work, hard work, and those hooves look really great when they’re done – but is all that attention really necessary? It isn’t cheap, either, getting those hooves worked on. Wild horses don’t get either guy to come around, and they survive all right. Shouldn’t a backyard horse need even less attention than a wild one – who, ironically, gets no attention at all? And even with all the guys’ visits, some hooves always seem to be in trouble, feet hurting for one reason or another. Why is that?
Now, that’s a lot to think about. Maybe I can shed a little light in the darkness surrounding this puzzling subject. We will at least get a little more familiar with hooves, I hope. Let’s start with a quick look at what makes up a hoof:
Meet Mr. Hoof
The hard covering you see wrapped around the hoof is called the hoof “wall”. It has two jobs: its outer layer – the part you see -- is armor plating, so to speak, protecting the foot from outside trauma. It also has an inner layer, whose job is to provide shock absorption, stability, and some weight support for the horse.
Referring to the bottom view sketch, you see some interesting items. The flat area in the front half of the foot and extending into the sides is the “sole”, and much like the sole of your shoe, it provides protection and support.
The arrowhead-shaped area is known as the “frog”. It’s soft but firm, and provides some weight support, but it is also a shock absorber as well as a stimulator for certain tissues internal to the back of the foot, known as the digital cushion and lateral cartilages.
You also see the “heels”, flanking the back end of the frog. Note that they make a sharp “turn” as they head back toward the toe, forming what are called the “bars”, before disappearing into the bottom of the foot. That sharp turn in the wall, one of nature’s strongest constructs, forms the primary weight support for the horse. Take a sheet of paper from a small notebook, stand it on its edge, then press down on the upper edge. It bends immediately, has no supporting strength. Now fold that sheet of paper in half, stand it on its end and repeat the process; that weak sheet of paper now gives surprising resistance to your pressure. The hoof’s heels work the same way, but can support enormous pressure – more than the weight of the entire horse. And if you were to watch the heels closely from behind when the horse is walking across a rocky area, you’d see the two heels of each hoof moving up and down on the uneven rocks with each step, independent of each other; this keeps the hoof “even” as the horse walks. You could consider the horse’s hoof as the world’s first fully independent suspension system, rather like that in your automobile, with the frog acting as a shock absorber and the heels as the springs.
Referring to the side view sketch, the triangular-shaped bone you see is called the “coffin bone”. It is actually an inverted cone, and is attached across its front surface to the inside of the wall by a Velcro-like substance forming what is called “the laminae”, or “laminar connection”.
The two bones above the coffin bone are known simply as P1 and P2 (the coffin bone is also referred to as P3). Together, these form what is called the pastern, terminating at the upper end into what is known as the fetlock joint.
Tucked neatly into the back of the joint between P3 and P2 is a small, rod-shaped bone, whose end view you see in the sketch; it is known as the “navicular bone”.
And finally, the side view sketch shows a wad of fibrous tissue called the “digital cushion”. Note that it sits just above the frog: when the hoof is healthy, it is stimulated by the frog with every step the horse takes. A large and healthy digital cushion is vital for good foot health throughout the horse’s life.
A bit of interesting trivia: the hoof on a foreleg of a horse is the equine equivalent of the end of your middle finger. In fact, the horse’s entire foreleg matches up with your arm, bone for bone, except he has but one “finger” -- the fetlock joint to the hoof -- while you have five. Evolutionary deviation.
The hoof at work
Compare a hoof to your own foot. The hoof is actually a very small appendage, considering the bulk and weight of the horse that it supports. But the horse is a prey animal, it relies upon its sharp senses and speed to get out of harm’s way, thus its legs are comparatively skinny, allowing the horse the broadest field of view while it’s head is down and grazing. And when he runs, given a couple hundred feet head start, he can outrun any other animal on the planet. Being small, those hooves are also relatively lightweight and don’t drag him down when in flight.
Since the species lives on almost every kind of surface imaginable, the feet need to be hard, strong, and virtually bullet-proof – and they are.
Their feet need to wear well, too – considering that western-American ferals move an average of 20 miles per day, they need all that toughness, and they grow constantly and consistently to compensate for all that wear. Why don’t feral horses require trimming? It’s because the rate of hoof wear just about equals the rate of hoof growth. How convenient! When there’s more growth than there is wear, Mother Nature steps in and trims the horse by chipping away where the wall meets the ground. The result isn’t pretty, but it surely is functional, and it all grows back.
Ferals may get their 20-miles-per-day, but certainly, domestics do not -- yet their hooves grow. Enter the trim guy. Horses living the barefoot life generally need attention every four to six weeks, because without sufficient movement every day, growth is greater than wear. The trimmer’s job is basically to remove the excess growth and restore the hoof to its ready-to-use condition.
Some horses are shod – but shod hooves also continue to grow. That means the shoeing farrier needs to remove the worn shoe, trim the excess growth from the hoof, then replace the worn shoe with a new one.
Shod or not, allowing a hoof to overgrow results in much more than just the loss of a nice appearance. Good foot health is likewise sacrificed – a subject to be covered in detail at another time. One common condition is the development of hoof chipping and splits. These are usually superficial conditions, correctible by proper trimming. With proper care, under normal circumstances both conditions will grow out. Remember, the wall has two layers. The outer layer is by far the most affected by chips and cracks, the inner layer not so much. That’s a good thing – it maintains the integrity of the hoof’s ability to protect, while any damage grows out with the growth of new wall.
What makes horses limp?
Quite a laundry list, here. Lameness can originate anywhere in the horse’s locomotive system, but most commonly in the feet themselves. We’ll talk about several of the causes.
Laminitis, one of the more common conditions, is also one of the more frightening – as well it should be. Laminitis is one of the most painful of hoof conditions, and the pain is long-lasting, even when properly treated. The Velcro-like structure that holds the wall to the coffin bone, mentioned earlier, is the laminar connection, which, like Velcro, consists of two layers that cling together tightly. But the laminae are living tissue, complete with millions of tiny blood vessels that carry nutrients to the cells that make them up. When blood flow to those cells is interrupted, the cells die, and when it happens to enough of them, the integrity of the connection between coffin bone and hoof wall is broken. That results in the very painful condition known as laminitis, with an additional danger – that of complete failure* of the laminar connection, allowing the wall to rotate away from the coffin bone, and forcing the hoof’s sole, already bearing much of the horse’s weight, to take up the added support load normally provided by the laminar connection.
Laminitis and founder are two conditions that require immediate attention by a professional. Both are treatable if caught in time, but the horse’s pain needs independent and immediate attention. Common practice is to dose the horse with an NSAID such as Bute or firocoxib, and to apply a special trim to take pressure off of the damaged laminar connection.
Abscesses can develop almost anywhere in the horse, but are most common in the hooves. An abscess is comparable to a “boil” in you and me – very painful to touch. Abscesses usually develop in hooves following a laminitis attack or founder. The dead laminar cells need to be disposed of by the body’s lymphatic system, but the infection is often so massive that the body can’t “keep up” with it well enough, and so it forms a pocket of infection. That pocket of pus and blood will eventually find a way out of the horse through a combination of normal waste collection process, and “popping” – that is, forcing its way out of the hoof, usually at the top of the wall (coronary band) or in the heel bulbs or through the sole. It is not unusual for a series of abscesses to develop after laminitis hits, as the dead laminae are cleared out. Abscesses can be dangerous if left untouched or handled improperly, and so a vet should be brought in early on to deal with them.
Bruising is caused by outside trauma. A hoof kicking forward onto a hard, sharp object may cause no visible damage, but may cause internal damage you can’t see. You’ll know it by the limp, which usually disappears after a day or two. You’ll eventually see the evidence -- some old dried blood in the bottom edge of the wall when it’s trimmed. More common is bruising on the sole, caused by the horse coming down hard on a sharp stone, for example. Soles are tough, but not nearly so tough as the wall, and so you will sometimes see evidence of that trauma when you pick up the hoof. Such a condition may require some treatment to prevent infection.
Navicular is a sort-of catch-all term that describes pain in the back of the foot. It’s named after that little bone, mentioned near the end of the Meet Mr. Hoof section, above. The name, “navicular”, gets the distinction of representing a variety of back-of-hoof problems because several are connected with the navicular bone itself. However, true navicular bone problems also involve some soft tissue, such as the deep digital flexor tendon and the sheath protecting it. Pain originating at the navicular bone is referred to as Navicular Syndrome – it happens when the sheath wears through and the tendon rubs directly on the navicular bone –that rubbing happens with every step the horse takes. Fortunately, it is a curable condition.
Underdeveloped tissues, the digital cushion and lateral cartilagesin the back of the hoof need to be included here, because although their pain is comparatively unspectacular, it is real, and it’s probably the most common source of chronic pain for domestic horses. That’s because a domestic’s digital cushion and lateral cartilages are rarely fully developed to properly support an active, full-grown horse, leaving the hoof weak and accident/injury prone. The key to a horse’s foot health is movement, movement, movement, starting at foalhood, to deliver stimulation to those soft tissues. Movement is great preventive medicine, and development of those soft tissues requires it constantly. Domestics rarely get sufficient movement for proper soft tissue development. So, ride that horse! Often!
Thrush and White Line disease
These are actually microbial infections, but they are so common that they deserve special mention here. Thrush is actually a condition caused by a successful invasion by a number of microorganisms, especially Candida albicans; essentially, it is a yeast infection. It commonly strikes the frog, and if unchecked eventually destroys that appendage. A healthy frog is well-formed, smooth, soft but firm, and makes initial ground contact when the horse walks. An infected frog can appear to be coming apart before your eyes; it is often soft and “mushy”, receding into the back of the foot, and when probed with a hoof pick, comes apart easily. It can exude a black, smelly substance. Left unchecked, thrush can infect so deeply into the foot that it can cause serious lameness and health risk. There are a great many products on the market aimed at combating the thrush condition, many of which are effective on some horses, but not on others. The most successful treatments include soaking in Oxine (chlorine dioxide), and spraying with colloidal silver.
White Line Disease is the term often assigned to a festering sore at the edge of the sole. However, true White Line Disease is a more serious condition that exists within the hoof itself. It is caused by an anaerobic fungus that grows within the laminar connection, where there is moisture, warmth and no air. The result of such an infection is the death of laminar cells, leaving hollow spaces between the layers, allowing new fungal growth to develop. Unfortunately, the degeneration that takes place within the hoof wall is usually not visible until substantial damage has been done, making this infection a silent threat to the well being of the animal.
Seems like the hooves are the gathering-place for all sorts of painful events. It figures, though, since the horse’s feet are constantly at risk just by being used. Of all the common hoof problems, probably laminitis and abscessing are the most worrisome because while the horse feels the pain, you see evidence of it by the way he moves. At least you get the message of the pain early on, and can take steps to help him immediately.
Why do we shoe hooves? How about barefoot?
The nailed iron horseshoe seems to have first appeared in Europe about 5th century A.D. It was quickly learned that in the conditions of the time, animals exposed to domestic work that caused breakage or heavy hoof wear needed protection beyond their natural capabilities. Thus, born of necessity, the nailed-on horseshoe evolved from the early efforts at protection.
As a result, it became commonplace to shoe domestic horses, a tradition carried on through modern times. However, today the horse is primarily kept as a pleasure animal, used for everything from competitive events, through demonstrations of equine grace and prowess at shows, pleasure riding, and yes, still even farming in some communities.
Advocates of shoeing horses point out that domestic’s hooves continue to require shoeing much of the time lest they suffer damage. There is, however, a large and growing movement toward reversion to the barefoot condition. Its advocates believe that virtually any healthy horse can perform a horsey task barefoot just as well as and usually better than its shod counterpart. They cite the natural condition as being much better for the horse, and present convincing arguments and examples to support their position.
Perhaps the jury is still out. Meantime, shod or barefoot, compassion for the horse demands that we provide him with the best possible hoof care.