Thursday, September 15, 2011

The Functional Frog and What Can Go Wrong

Who on earth looked at the bottom of a horse's hoof and thought "I will call that part... THE FROG!".


A near perfect frog, from a hind hoof.
The frog's function is to be an essential part of the landing gear at the back of the foot. It acts as a shock absorber along with the digital cushion. Also, when the hoof hits the ground, the frog compresses and squeezes blood back out of the foot and up the limb again.*Edit 29.10.11: there is some research that suggests that when the hoof is loaded, the dropped frog and sole actually create a vacuum ad suck blood into the hoof, rather than pushing it out! Must investigate this further... Ok, carry on!* I like to say that a horse has five hearts - one in his chest and one on the underside of each of his feet. :)

Correct movement = heel first landings = the force of the hoof hitting the ground being dissipated throughout the structures designed to do just that, limiting concussion.

The frog should look plump, open, flat and healthy. It should be wide at the heels. The central sulcus should look like someone has pressed their thumb into pliable putty, not look like a deep crevice. It should be free of thrush, and have passive contact with the ground in the stationary hoof. On soft ground (where the hoof would sink into the ground when loaded) the frog should be further away from the ground than on hard ground, where the frog is normally at heel height

The frog should take up 2/3 of the hoof

The frog should barely be trimmed at all. The only trimming a frog would need in most circumstances is to open up any areas that thrush would be hiding under.

Here is a trim I did on Gracie. Compare the frog before (left) to after I finished the trim. All I have removed is anything that was harboring thrush but did not remove anything she would need. (Ignore the terribly uneven heels - this was fixed after photo was taken!)

I found this on the internet - the whole frog needing to come off as there was a severe thrush infection under there. Thrush is painful! This horse would need boots and frog stimulating pads (depending on how comfy he was in them) on 24/7 til the frog calloused and came back to life I would imagine.

The frog should NEVER be trimmed like this, no matter how pretty that looks!
If the frog is compromised in any way (thrush and over trimming being the most common), this leads to flat or toe first landings. If the hoof is trimmed (or shod) in such a way that the frog is taken out of it's secondary weight bearing duties, then the hoof will contract up, the central sulcus will form a deep crack and provide a nice comfy house for thrush to thrive, and the frog will no longer be fully functional (if at all depending on the amount of contraction).

Frog has become too passive due to thrush infection (looks like it is clearing up though)

Severely contracted hoof and frog.
Top is a fairly normal hoof with frog having passive ground contact. Bottom is a contracted hoof with the frog suspended out of contact with the ground unless the ground was very soft.

So consider the frog when trimming - leave it alone unless there is thrush present, then take the bare minimum you can. Keep it clean, and in passive contact with the ground. Most of all, trim for heel first landings! If a horse is landing heel first, the frog will pretty much look after itself.


  1. Why not come and post this interesting blog on a new Equine Blogging Network We would love to feature your blog on there!

  2. You have a very interesting and informative blog. I really enjoyed this frog article. I will have to look around!

  3. Thanks Val! I try to write articles that really cement the concepts in my brain. It helps me learn too!

  4. How does one check for thrush? Is it just the smell or are there any other signs? Also, what does thrush actually to do the frog? Make it shrink?

  5. Signs of thrush include the smell (which can be quite subtle unless you stick your nose right in the collateral grooves - not recommended!), the presence of black colouring, the horse can present as footsore, and the frog especially can look ratty or have the look of a sea sponge. Thrush eats away at the healthy tissues, causing pain that can set the whole hoof to land toe first.

  6. Too often we get caught-up in fixing symptoms and not looking for the root cause. The root cause is not the invasive pathogens that are weakening the frog but the under running or contracted heel. The lameness in most cases is from unbalanced stresses on the digital cushion and incorrect alignment of the lateral cartilage. The solution is moving the heel so the major weight bearing is back under the horse.