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Your Horse from the Ground Up - Part Two - The Hoof
 By mosquito   •   16th Jun 2012   •   7,052 views   •   11 comments
Now it’s time to take a look at what’s going on inside your horse’s hoof – it’s just as fascinating as all the structures on the outside, and just as important to your horse’s health.

First, let’s talk about the bones inside the hoof and what they do. The pedal bone is the largest bone in the hoof, and it acts like your horse’s toe. The angle of the pedal bone is a big factor in your horse’s conformation and movement, and if it has a bad angle – either too steep or too shallow – your horse’s way of going can be adversely affected. When you look at the conformation of your horse’s lower leg, it’s common to pay attention to the pasterns and fetlock, but this time, take a good close look at the angle of the hoof. Watch how the pastern flows into the hoof – does this look like the same angle as the hoof wall? If the wall looks like it has a significantly different angle to a continuation of the pastern bones into the hoof, you might want to talk to you farrier!

Horse Hoof Anatomy

The position of the pedal bone can change, so don’t rest easy that your horse’s hoof conformation looks good today. A horse that moves continually on poorly trimmed (or untrimmed) hooves, while lame, or kept for extended periods confined to its stable, can find that the angle of the pedal bone adjusts to adapt to an unusual way of moving (or not moving at all). Illness can also cause the pedal bone to ‘rotate’, or the angle shift downward. Heels are too long (or ‘high’) can force the pedal bone into a downward (and lameness causing) position.

Horses with any condition that increases the pressure inside the hoof, most commonly an infection or laminitis, are prone to pedal bone rotation as the pressure in the hoof forces the pedal bone downwards. In fact, the term ‘foundering’ refers to pedal bone rotation. One the pedal bone has rotated, you have a very serious – and sometimes irreversible – condition. In severe cases, the pedal bone can even push through the sole – if this happens, there is often no choice but to put the horse down, or at least a very long recovery process as the hoof grows out again completely.

The pedal bone is held in place, and moves the hoof, by two ligaments, one down the front of the pastern and over the bone, and one down the back. The one down the front (the flexor tendon) seldom causes any problems, but the one down the back – the flexor tendon – well, that’s another story! One of the most common problems of the flexor tendon isn’t the fault of the tendon at all, but of a tiny little bone that sits at the back and the top of the pedal bone – the navicular bone. Horses with poor conformation – usually very ‘upright’ pasterns, where there is a sharp angle between the pastern and the hoof – poor hoof trimming, or simply a genetic predisposition to porous bones, can develop ‘navicular disease’.

In this condition, the navicular bone becomes rough and porous, and continually aggravates and damages the flexor tendon as it rubs over the bone. Horses with navicular are often lame, and sometimes show symptoms similar to laminitis, such as standing with their front feet stretched out in front of them, or with their front feet on a hill – all to ease the pain and inflammation of this uncomfortable condition. Horses with low trimmed heels are especially prone to navicular, as are horses with very steep pasterns. If this is your horse, talk to your farrier about trimming and shoeing options that can reduce the risk of the condition developing, or ease discomfort once it has.

There’s some other stuff going on inside the hoof too. Remember how we talked about how the hoof was important for your horse’s circulation? Well, wrapped around the pedal bone, and filling up most of the space of the hoof, are the ‘collateral cartilages’. These are made of cartilage (like your nose or your earlobes), which means they can flex and bend as the horse steps and puts pressure on the hoof and sole. As they flex and contract, then spring back to their ‘open’ position, they help to push fluid and blood up out of the hoof, thereby helping the horse’s heart do its job.

Underneath the collateral cartilages, and cushioning the pedal bone, is the ‘digital cushion’. Notice how we see ‘digital’ often? It doesn’t mean anything technical; in anatomy digital refers to anything to do with a finger or a toe, and your horse’s hoof is, in fact, its toe. Anyway, the digital cushion is another piece of cartilage, this time a squishy flat pad that compresses between the pedal bone and the sole as the horse steps, helping to flex the phalanges by pushing them out of the way, and then snapping back to push blood back up the horse’s leg. Interestingly, this springing back of all the cartilage in the hoof also eases strain on the flexor tendon. It’s not uncommon for horses with flexor tendon problems (which we’ll talk about when we get to the lower leg) to also have structural problems in the hoof. Bad hoof trimming and shoeing can not only lead to hoof trouble, it can even cause severe conditions like bowed tendons, because the flexor tendon ends up taking on too much of the work or moving the horse’s leg.

Horse Hoof AnatomyJust as the pedal bone position can change in certain conditions, so can these cartilaginous structures. In fact, as horses get older, it’s quite normal for the softer structures inside the hoof to gradually harden. Often what looks like arthritis in older horses – shorter, stiffer steps – is actually a response to the cartilage hardening and restricting the full movement and effectiveness of the hoof. This condition is called ‘sidebone’, and in advances cases you can see the hardened cartilage as a hard ring around the pastern just above the hoof, where the top of the collateral cartilages can be felt. Can it be prevented? Well, limiting the demands placed on the cartilage can help delay the onset, so as your horse ages be more careful about riding on hard ground where there is a lot of compression in the hoof, and work with your farrier to protect your horse’s soles. Once the cartilage calcifies though, it’s irreversible, although clever shoeing can keep your horse comfortable and rideable in many cases.

The last really important structure in the hoof is the ‘laminae’, which is the fibrous, fluid and nutrient rich structure that attaches the pedal bone to the hoof wall. There’s actually two laminae in each hoof; one attached to the pedal bone, and one attached to the wall. The two ‘sides’ of the laminae meet and intermesh in a complicated patchwork. In fact, it’s such an intricate woven structure that there’s actually about 15 square feet of laminae inside each hoof – that’s the same as a 3 x 5 rug! Why is there so much? Well, if you think about it, the pedal bone – and therefore all the weight of the horse – is hanging, almost in mid air. The laminae are the ‘slings’ that hold the whole horse up, balancing on the pedal bone. Every time your horse takes a step, the laminae have to hold the pedal bone in place, and so they take most of the weight of the horse – about two thirds of the force of each step is borne by the laminae; the rest by the cartilage and the sole. This is why – if you ride on hard ground – you may find your horse gets ‘hot feet’, where the hoof wall feels hot to the touch. This means there is inflammation in the laminae, and your horse’s laminae need some rest

Usually the laminae cause no problems, but they are the only part of the hoof that can really ‘hold water’. That means that if there is an infection in the hoof or if circulation is poor and fluid builds up in the hoof, it’s the laminae that suffer. When there are circulatory problems, the most significant – and serious – symptom is laminitis. This is where the laminae become seriously inflamed, causing immense pain (remember, trapped in the hoof there’s nowhere for that swelling to go), forcing the pedal bone to rotate like we talked about earlier, and in very serious cases that inflammation can break through the coronary band or at the ‘white line’ on the sole as the hoof and the wall are pushed apart by the inflamed laminae. Laminitis is usually associated with diet – and overfeeding is certainly a very common cause – but any time there the horse’s natural circulation is impaired, laminitis needs to be prevented. This means if your horse has to be stabled for a long time, you should talk to your vet about steps you can take to improve circulation and reduce the risk of laminitis.

So that’s the inside of the hoof – next time we’ll take a look at the amazing, complex, and delicates structures of the lower leg.
Summer Rain  
Great aricle!
  Jun 16, 2012  •  6,221 views
 
weezapony  
Wow, this is so detailed, I really learned a lot! :D Thank you!
  Jun 16, 2012  •  6,233 views
 
RoyalCrownEstates  MOD 
Wicked article.
  Jun 16, 2012  •  6,406 views
 
Sapphire Flames  
wow.wonderful article! :)
  Jun 16, 2012  •  6,205 views
 
Double Spur Ranch  
good article!
  Jun 17, 2012  •  6,218 views
 
Anabel6931  
Cool!!!!!!!!!!!!!!!!
  Jun 17, 2012  •  6,219 views
 
Let It Ride  
I love the picture with the bones. Very interesting
  Jun 18, 2012  •  6,219 views
 
HITW  
An excellent and informative article! Bravo!
  Jun 22, 2012  •  6,416 views
 
Moose  
Wow! This is a lot more interesting than I had expected! When I saw the article I pictured it saying something like, "And this hard thing is called the hoof, children. It's what the horse walks on." No but this is farr more interesting. It sounds a lot like what I studied in hippology. (That's the study of the horse, not the hippo.)
  Jun 22, 2012  •  6,267 views
 
Anabel6931  
Wow! I learned loads!!!!
  Jul 1, 2012  •  6,444 views
 
Cowzers  
I learned a lot from this, thanks for another great article !
  Jul 4, 2012  •  6,215 views
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