Shedding Frogs in Horses

Around this time of year, as it’s Spring here in Canada, you’ll find a lot of articles written for and people talking about shedding frogs. If it’s your first time owning a horse or just paying attention to their hoof health then it may be concerning to see large chunks of frog coming off. You’ll search around on the internet and find most people saying not to worry about it, it’s normal in the spring and fall. Horses just shed frogs and that’s that. It’s a bit rare to see an article really get into it though and it seems more anecdotal about frogs shedding, rather than producing proven theories or medical evidence of why this happens. So let’s talk about that a bit, I have a theory. First off though, here is a frog shedding off:

[responsive]Shedding Frog[/responsive]

The short answer to the question of, “why is my horse losing it’s frog?” or, “is the frog peeling off a good thing?”, or “what is this piece of flesh coming off the hoof? is my horse dying!?”, is simple though.

Yes, it’s normal and yes it’s happening for within the best interests of the horse’s health. The question is, why is it happening? This is where the articles usually stop and just say “because the ground gets wet” or “soft” or “it changes” and in turn the frog sheds. So we definitely have a reliable situation where this happens in. From here though, we have to start talking about the anatomy of the hoof. For a quick overview of the anatomy, this is a decent article. Here’s what shedding looks like in the beginning:

[responsive]Frog beginning to shed off[/responsive]

The visible part of the bottom of the hoof is comprised of the sole and frog and a bit of hoof wall. We’ll lump being shod and barefoot into one category of “the peripheral loaded area” because that is what a long hoof wall will do and what a shoe does. The whole hoof becomes loaded onto the outer wall of the hoof, hence “peripheral”, being the outside edge. The depth of that is what is important here.

So if we start by imagining what a hoof does when it lands for both peripherally loaded ones and evenly loaded ones where the sole and frog can touch the ground. Let’s start with peripherally loaded (PL foot) ones.

In a PL foot and hard ground, only the outside edge makes contact with the ground and the horse is suspended from the ground on the laminae within the hoof. The only connection the hoof wall has to the foot itself is tissue. Very strong tissue, but just tissue. The bone does not connect to the hoof wall, much like your fingernail. In the case of hard ground it’s impossible for the sole to share any load and unless the frog is very overgrown and thick, it too will not touch the ground. For soft ground, no problem as the hoof will sink in and the whole hoof will again properly share the load of the horse.

For a horse that is not shod nor has long hoof walls, they will take steps on both hard and soft ground with at least the hoof wall and frog making it to the ground to share the load. The very outside edge of the sole almost may hit the ground, but if there is proper concavity, that’s all that should touch. Again, on soft ground the whole hoof shares the load as it’s designed to do.

Let’s take a look at what happens when the frog takes part of the weight of the horse, as we’re concentrating on why shedding frogs happen and if it’s ok. Beneath the frog is the frog corium. Just like the sole corium, this area of the hoof is what supplies all the nutrients to the frog. Blood travels through in large amounts when proper load is applied as it acts somewhat like a pump. Just try to press your finger down on a table hard enough to remove all the blood. It turns white. When you lift it off and take the pressure away it turns back to the normal color as blood is able to return. This is no different than a pump system and is exactly how the hoof works. Here’s a week later, that same frog slowly coming off and new growth underneath:

[responsive]Frog partly shedding off[/responsive]

If we continue with that line of thought then we can assume that a frog that receives contact with the ground in regular intervals is able to healthily move blood around in the foot. If it never touches the ground then it’s solely dependent on the horse’s heart moving the blood, and if it always touches the ground then the blood can’t get in very well. I would expect we can safely assume that the hoof needs this regular change of blood as often as possible with the right pressure. That would be healthy.

So as it goes, when we go from winter to spring the air warms, it rains and the ground gets soft. It gets wet too but I’m not sure if that’s the part that really matters.

If we take a look at what the frog actually is, it’s well accepted that the frog is like a big callous. It is there to protect the inside of the hoof and provide cushion and displacement of pressure as the horse lands. It is the softest part of the hoof and needs to harden up to properly protect itself both from sharp objects, rocks and sticks, and of course bacteria and fungus. All of these points are important when we think about why it would bother shedding.

For the most part frogs will slowly flake off. Completely and totally normal as it continues to grow down from the corium. Bits and pieces come away, trimmed off by the hard ground the horse steps on or by a trimmer’s or farrier’s knife. Most horses can manage their own frogs. It’s when the ground hardens up that the frog hardens up and reaches down level to the peripheral loaded level. The corium again receives that wonderful intermittent pressure and the foot can feel it’s way around. The lateral cartilage also gets the workout it needs and all is well.

From here is where the transition happens from big healthy hard frog, to shedding weak and missing frog. Not in the regular slow way of flaking or peeling off a bit at a time, but in a quick way where up to three quarters of inch of thickness can come off. We go from hard ground to mushy ground and suddenly the frog is getting a lot more pressure. Instead of needing to reach all the way down to the heels to get pressure from the ground, the ground is coming up to meet it.

When this happens the hoof responds by ridding itself of a large portion of the frog. I would almost say that it is doing it in an emergency manner as it either hurts too much or inflicts enough trauma to the corium that a bruise forms and the next layer of frog that is created is separated from the original layer. The two layers become separated and hence you get the shedding. Here we have what the frog looks like after cutting off what was ready to come off:

[responsive]Shedding Frog cut off of hoof[/responsive]

and another as they’re a bit blurry:

[responsive]Shedding frog cut off of hoof 2[/responsive]

Here is a different horse in drier conditions. Shedding of frogs isn’t always about the seasons or if it’s a change from wet to dry or dry to wet. This particular hoof has been under a lot of stress in heel area and it’s shedding material all over and growing very fast. None of the frogs on this horse’s other feet are doing this. So going on the above theory, we are again looking at a hoof that is self managing. We tend to just help it along a little bit when it’s come along enough that it’s clear the old frog isn’t needed anymore.

Here is a before pic:


Frog being pulled and checked. Note the chalky white appearance. This part of the frog is unneeded anymore to protect the underside. It can be removed safely and should be in the case that he accidentally catches it on something and tears it off.


Here is the after shot showing a healthy frog underneath.


We’ll wait a little longer to see if dealing with the back of the foot is required. It may just shed itself off naturally but we’ll be looking for that chalky white appearance to take off. The important thing to consider is that the frog underneath must be mature enough to be able to handle touching the ground.

So, if this theory is correct, which I believe it is, the frog shedding is a healthy response to an unhealthy situation. The best thing to keep in mind is to make sure not to remove that shedding frog without making sure the frog underneath is strong enough to resist penetration by rocks etc. It should be reasonably calloused or it will not protect the inner structures of the foot and it’s likely to shed again as it is subject to trauma again. Most frogs can just shed on their own, but if you’re finding that lots gets trapped in between the layers, then it may be required to trim some of it off.