One thing that is very important to check out on your horse when looking at the feet, is the soles. The sole is the bottom of the foot that isn’t frog or wall or the white line. The sole is the same material as the wall, but a bit softer. The thickness of the material is what we’re talking about here.
Thin soles are what happens when the hoof can’t make enough material to protect the corium, coffin bone and all other internal parts of the hoof. Check out our article on basic anatomy of the hoof here. Surprisingly this is very common in this day and age and there are very few owners who are alerted to the danger of the thin soles until it’s too late.
Leaving a horse in this condition is a time bomb just waiting to go off as it becomes very easy to bruise the internal side of the sole with a rock or hard stick. When this does happen, it’s the horse that suffers and sadly many are put down for it as thin soles can go so far as to lead to protruding coffin bones and abscesses. Many times these aren’t something that a lot of people want to or can possibly deal with both in time and money.
If you look at the picture for this article, you may be able to see that it is a great example of what a thin sole looks like. This picture is from an 8 year old thoroughbred mare who has likely had shoes on her whole life. This horse is one sharp rock away from a puncture, or at the very least a very bad bruise. In the middle of that is damage enough to cause an abscess, which is the equivalent of spraining your ankle. Hurts more and takes longer to heal than a break.
Thin soles don’t just happen on horses naturally. In fact, thin soles are the anomaly for horses in a natural environment, most have at least 1/2 inch thick or more of sole protecting the internals of their feet. The sole of a horse is very important and works in conjunction with the hoof wall and frog to share the load of the horse’s weight as it moves about. Unless the environment that the horse lives in is perpetually wet, the sole will generally be quite hard and impermeable to most things outside of nails sticking straight out of the ground. Soles can get bruised by stepping hard on big rocks or sharp ones, but it’s much less likely the thicker the sole.
While there is quite a bit of theory about how the sole grows, it is my impression and understanding through both study and practical experience that most of the sole grows outwards from the frog area. The horse’s foot is a very advanced part of their body and has evolved and grown to fix itself and adjust itself quite well to it’s environment. This is exactly what is happening when the sole gets thin.
Something in the environment has caused the sole to stretch out and get thin, the horse doesn’t want it that way, but the body has adjusted and that is the result. Now, the horse may be trying really hard to do what it’s doing AND grow in a healthy thick sole, but in a lot of circumstances it can’t happen. The main reason this may happen is where the human steps in and removes healthy sole that needs to be there.
The second is primarily about some form of trauma, like a form of founder or laminitis that affects the internal pieces of the hoof and in turn causes less sole to be created and applied. Good sole growth requires good blood flow, damage to the corium can be very damaging to the hoof. When a horse does become foundered it essentially has taken steps to protect the internals but unfortunately this causes a lot of problems and unfortunately these problems don’t fit into the schedules of humans that want to ride.
What generally happens here is that the hoof has decided that the hoof wall needs to move off of the coffin bone and it creates even more keratin material between them both and you then have flared walls. This extra keratin isn’t hard like the hoof wall and in fact is quite soft, in turn, it doesn’t provide much protection without the hoof wall there. Here lies the problem that you have to get the hoof wall to grow back in line with the coffin bone, which is why a foundered horse needs patience and regular maintenance that most won’t or can’t provide. So, they stay that way. Surprisingly some do quite well considering the damage that is being done and likely the pain inflicted each step or jump.
Back to the sole, we now have a situation where the hoof wall is being forced away from the coffin bone and the sole has to accommodate to create more sole and stretch out to match. Then, there is an inordinate amount of keratin now being created for this wedge instead of being dedicated to creating sole and hoof wall. It isn’t much time before you have thinner soles and as I’ve noted above, it doesn’t get dealt with and the critically thin soles become reality. Most at this time are heavily encouraged to shoe the horse to get it off of it’s painful soles and you now have a recipe for NEVER healing properly.
Here is another great example of a thin sole, as you can see at the apex of the frog that it blends almost seamlessly into the sole. Understanding the anatomy of the equine foot proves that there is very very little sole on this horse after removing long time shoes:
The soles of a horse are 1 of 3 components of the foot that help bear the load of the horse. Unless there is an anomaly where the sole has become too thick or a false sole is hiding the real sole, you’d never touch it. The horse can manage it’s own thickness just fine without any intervention, in healthy cases. When combining the frog and hoof wall with the sole, it can, and is supposed to, completely support the horse through all gaits, jumping and just loafing around on any surface it feels like.