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Cindy Nielsen DVM

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How many feet on a horse?

Description of laminitis and founder

HELP! My horse has foundered and no one seems to be able to fix him/her!

First, let us take a look at some anatomical features of the equine hoof that will help you understand what has happened with your horse.  

hand hoof

Equines – and only equines (including horses, donkeys, mules, zebras, minis, ponies) – walk on the very tip of what is equivalent to our middle finger or toe. The photo below shows the bones in a horse’s hoof, and a human hand, with corresponding structures colored the same.  MC3 and 2 are the “splint bones” or metacarpals 2 and 3, the remnants of the bones in the hand colored yellow and orange, on either side of the middle finger.

Click on images for large view

All of the white bones of the hand are no longer present in the equine digit, lost through evolution or the hand of God, per one’s beliefs.  This is truly an amazing feature of our equine friends, to have their entire body weight suspended on one bone of one digit in each limb. No other furry critter in the animal world can make this claim.

The bone labeled P3 is the coffin bone, or third phalanx, which is inside your horse’s hoof.  In the  photo one can see the bones of hoofbonesthehorse’slower limb as they are oriented in the hoof capsule; the coffin bone itself is barely visible as it sits inside the hoof wall (you can see the very top portion of it only in the photo).

The coffin bone is covered by a series of leaflet-like structures called laminae (plural for lamina), specifically “dermal” or “sensitive” laminae, containing blood vessels, nerves and connective tissue.  These sensitive laminae interdigitate with “insensitive” (no blood vessels or nerves) laminae on the inner surface of the hoof wall, creating a super strong suspensory apparatus that literally suspends the horse’s entire body weight in the hoof capsule.

photo 03 photo 04 photo 05

Now look at the following schematic of the inside of a hoof – all contents have been removed leaving only the hard horny part of the hoof capsule.  This shows the “insensitive laminae”, which interlock with the sensitive laminae – the bond between the two sets of laminae is strong enough to hold the horse’s body weight, WHEN it is healthy!

photo 06  photo 07 

Laminitis literally means inflammation of the laminae. When the sensitive laminae are inflamed and damaged severely enough, their bond with the insensitive laminae is broken, and the tissue suspending the coffin bone from the inner hoof wall fails. There is literally a disintegration of the lamellar attachment apparatus.  This would be akin to your finger nail separating from the underlying nail bed – OUCH! Only difference is, and it’s a huge one, the horse has to walk on his finger/toenails.  We don’t…

So what is founder? Founder means the damage to the laminae was sufficient  to allow the coffin bone to disconnect and rotate away from the hoof wall, usually in a backward and downward direction because there was complete separation of the sensitive (dermal) laminae from the insensitive (epidermal) laminae.  This complete separation does not occur in all cases of laminitis; some horses experience a bout of laminitis but do not progress to the point of foundering – these are the lucky ones. Thus, every founder case has and/or had laminitis, but not all laminitis cases founder.

The following photos are of a preserved normal hoof and lower limb, with the hoof wall and all soft tissues removed from one half of the specimen so you can see the normal anatomy inside your horse’s hoof. Notice how, in the first and last photos of the series, the front of the coffin bone lines up parallel with the inside of the hoof wall.

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 The next photos are of one normal (first photo) and one foundered hoof (second photo) cut down the middle, i.e. on a sagittal plane, so it is easy to see the relationship of the coffin bone to the hoof wall at the toe.  In the normal hoof they are parallel. In the foundered hoof the coffin bone has pulled away – down and backwards – from the hoof wall at the toe, and it is almost penetrating through the sole.

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