The hoof mechanism

Now that you know what the back of the hoof is made of you can understand how the hoof mechanism works. In a nutshell: When the horse weights a foot, that weight pushes down and expands the digital cushion which flattens out the live frog and pushes the lateral cartilages outwards. When the weight is taken off the hoof the live frog springs back to its original shape and the lateral cartilages move back in.

Makes sense, right? Check out Cheryl's collage below for a visual aid.

The hoof mechanism needs certain conditions to work correctly, for instance the foot must be disease free and the shape of the capsule (hoof wall) must allow the hoof to expand and contract. That means no thrush, no imbalance, and no contractions of the hoof wall- any of those will impair the hoof mechanism and will result in negative impacts on the joints.

• If the digital cushion is too thin then too much pressure is placed on the live frog, it can't absorb all of it and transfers it to the heels, they can't absorb it either so they get crushed. At the same time, the shock that should have been absorbed by the digital cushion gets sent up the leg, creating joint pain all the way up to the back.
•  If the live frog is weakened by disease it can't flatten and spring back into shape, this causes pain and doesn't adequately push apart the lateral cartilages, this will also put too much pressure on the heels. Again, this will increase the shock sent up the leg. 

 See how this all works together?

You know how they say that each hoof acts as an ancillary heart for the horse? I estimate that it is the hoof mechanism that serves that function. Remember how I said the lateral cartilages are full of blood vessels? The hoof mechanism essentially "pumps" those lateral cartilages, moving the blood up and down the legs.

"But but but," you say, "I thought that was the frog."

Not a chance, the frog doesn't have any blood in it so how could it pump any? Speaking of frogs, here's another bit of info that might blow your mind, it certainly almost caused a mutiny in Oregon: The callused frog, the bit that touches the ground, is not essential to the hoof mechanism. Chew on that for a minute.

Are you leaping around and shouting now? So were we. Cheryl's theory is that the callused frog, the bit that touches the ground, is only there for comfort and protection- it's the live frog that acts as a trampoline supporting the hoof mechanism.

This theory actually gave me quite a bit of relief. You may recall that I had to cut Coriander's frogs off after his awful thrush infection last fall. I was sweating bullets that I was causing him harm by doing so, except that after I did it he was instantly more comfortable. It makes sense now, I treated his live frog and healed it from the thrush and then I took off the uneven pressure created by the nasty remains of the callused frog. Voila! Sound horse, without any frog touching the ground.

Here's another thing that might shock you to read me saying: Shoes don't shut down the hoof mechanism, they only hinder it. There's a good reason why farriers don't put nails close to the heels, they know that they move outward and won't hold the nails. If you have your horses shod ask your farrier to show you the heel wear the next time your shoes are set, you'll probably see marks in the metal from the heels moving in and out.

Does that mean I'm rethinking keeping my horses barefoot? Nope. I still don't like shoes because of the added concussion landing on metal adds to the joints, that they take away the heels natural independent suspension, that they open up the hoof wall to fungus and bacteria via the nail holes, and mostly because they force the horse to stand on their laminae (via the hoof wall). Again, I believe horses should stand on their soles, not the hoof wall.

If this has piqued your interest, Dr. Bowker has an article you might want to read here.

The back of the hoof

You may or may not have noticed that my previous hoof posts were suspiciously lacking in some pretty important structures. I was aware of their absence, the problem was that I still didn't really understand how they worked. Fortunately I got some insight in Oregon.

Have you ever heard that the hoof should be divided into thirds as shown by the photo below?

Photo from Yvonne and James Welz

 There's a reason for that: The back 2/3 of the hoof absorbs shock.

Since horses weigh quite a bit it makes sense that most of the foot should be devoted to energy dissipation, right? Okay then. Three important structures make up the back of the hoof: the digital cushion, the live (sensitive) frog, and the lateral cartilages.

The Digital Cushion

You could think of the digital cushion as the horse's gel insole, its only function is to absorb shock. When horses are born the digital cushion is simply a mass of fatty tissue, as they grow and move that fatty tissue becomes denser and cartilaginous. This is a good thing: thicker, tougher digital cushions are better able to withstand the pressure of a thousand + pound horse running around on them. Below is a picture of a nice, fat digital cushion- it's the white bit between the red of the coffin bone/corium and the grey of the frog.

Photo from I don't remember where, probably one of Cheryl's

Digital cushions need lots of heel first landings to develop but, sadly, a lot of domestic horses don't get them. Due to containment practices (stalling), shoes, and untreated disease lots of domestic horses suffer from poorly developed digital cushions. You can check your horses' digital cushions like this:

Photo from the Natural Hoof UK

They should resist your fingers when you squeeze, if they're soft and spongy then you've got a problem. The good news is that any horse at any age can develop strong digital cushions given the right conditions. The Rockley Farm blog gives some great examples of that. Whenever they show pictures of their rehab horses' improved heels what you're actually seeing is the development of the digital cushion.

The Live Frog

The live frog sits directly underneath the digital cushion, it is made of a solid, rubbery material that acts like a trampoline and produces the frog callus that we are so used to seeing and fretting about (at least I fret about it). Can you see how it's folded up like an accordion? That allows it to stretch and flatten under the digital cushion as the horse weights the foot, when the foot is unweighted the live frog springs back to its original shape.

Photo from Cheryl Henderson

I included this second photo so you could place what you were looking at in the above picture. Like the digital cushion, the live frog is also susceptible to negative forces, especially thrush. With bad cases of central sulcus thrush the live frog will get eaten away, weakening the structure and thus destroying an essential part of the hoof mechanism (I'll describe the hoof mechanism in another post).

Photo from Cheryl Henderson

The Lateral Cartilage

Raise your hand if you've heard of the lateral cartilages before (as if I could see you). I'm guessing most of you aren't raising your hand. That's too bad because they are quite important, not only are they key factors in the hoof mechanism, but they also contain lots and lots of blood vessels (and one exciting revelation- read on).

Each hoof has two lateral cartilages that are set up as mirror images of each other around the bones and digital cushion. They are located inside of the corium and have multiple attachments: They attach to the hide above the coronet band, the coffin bone, and P2.

Collage and photos by Cheryl Henderson

Here's the exciting revelation: The bars of the hoof grow from the lateral cartilage.

Okay, so maybe that's not as exciting as winning the lottery but it's still an important finding. It means that one side effect of leaving the bars alone and letting them overgrow is that they "jack up" the lateral cartilages which displaces them, squishes them, and basically keeps them from doing their job. Here's a rule of thumb for you: if you have to trim the walls then you will also have to trim the bars. If the horse isn't moving on enough abrasive footing to self-trim the walls then they aren't self-trimming the bars either.

Get it? Got it? Good.

OSNHC

I'm back! Did you miss me? Heh, heh. I finally got home yesterday afternoon (half a day late, thanks to San Francisco weather) and am now feeling rested enough to cobble together a post. I spent all last week at the Oregon School of Natural Hoof Care in Jacksonville, Oregon learning even more about the ins-and-outs of hooves and trimming.

If you want to learn more about hooves and trimming I whole-heartedly recommend taking their Whole Horse course. I chose this school because after all my research I felt that Cheryl Henderson was the person I could learn the most from and I wasn't disappointed. You might find some naysaying if you google her on the internet but don't believe everything that you read, Cheryl is a trailblazer and in her hunt for knowledge she's taken on many a horse that everyone else had given up for dead- she has guts like you wouldn't believe.

Anyway, back to my experience. I arrived late on a Friday evening, we pulled up to a house that looked like a hotel and were escorted inside. Cheryl had us drop our bags by the door before we walked through an enormous kitchen and out the back. We walked out onto a huge back deck overlooking a pond with a waterfall and a yard full of little lighted butterflies twinkling in the flowerbeds. I asked if we were in paradise and one of my fellow students told me that yes, we were (he'd been before so he already knew).

That set the scene for the whole week. Between Cheryl's beautiful landscaping, the hot tub, the sauna, and  the scented oil massage I got it was like staying in a resort. Then there was the learnin'. Everyday started with a lecture and then it was out to the barn for the hands-on experience with the help of the co-instructors. My class was made up of a group of people who had never trimmed, those who had already established a clientele they trimmed for, and one world class farrier. I even shared a room with Laz's new trimmer over at Sweet Horse's Breath (it's a small world after all...). It was a diverse group but we all got along like gangbusters, so much so that our class was named "Harmony."

Over the course of the week I trimmed four horses. The first was a 38 year old! pony who was blind, had no teeth, and was a total sweetie for me. Stupid me forgot to get pictures though. Then I trimmed a donkey:

Me, getting to work

Cute little donkey foot

And a paint mare that was brought in. She was also super sweet for me (there's a picture of me trimming her floating around somewhere, I'll post it when I get a copy), which was a good thing because her feet were quite overgrown and needed some work.

Paint mare pre-trim

Paint mare post-trim, check out the bruising, also the imbalance. This is why pictures are good.

Here I am taking a breather while Sparky got a White Lightning soak after I trimmed him. This little guy came in obviously feeling quite bad. He showed signs of DSLD and what we thought was a pretty bad sheath infection so we spent the day convincing the owner to get a vet out ASAP. Fortunately the guy took our advice and got someone out the next day. Diagnosis: Terminal cancer. That was that for Sparky, poor guy, but at least he's not in pain anymore. So it goes...

Despite that note of sadness it was a great week and an incredible experience. There's a post or two I want to make about what I learned but I want to ask Cheryl for her permission first- so keep an eye out for those. In the meantime, I'm off to trim a horse tonight!