The Caudal Hoof

The hoof should land fractionally heel first. As the limb is being retracted, the hoof glides into touch down and begins to accept load. Peak load is reached as the horse’s weight passes over the vertical axis of the limb. The faster the pace, the more fractional any given phase of the load bearing part of the stride is. 

The optimal alignment of the bones of the limb in movement and at rest are critical to the efficiency of the locomotor system – and to hoof health.

The ability of the heels to laterally expand slightly under load and the engagement of the soft horn/tissue complex at the back of the hoof are vital elements of shock absorption and of the optimal circulation of blood.

The attachment of the wall/ bars and sole to the tough but flexible lateral cartilages, combined with the frog/digital cushion/bulbs complex, allows the heel region of the hoof to deform laterally under load and also to displace vertically on uneven ground. The degree to which it can and should do this varies, but either too much or too little expansion under load will have consequences for the health of the hoof and potentially the whole horse.

The Bulbs

The bulbs should be broad and deep.  The hairline, when viewed from the heel, should be more or less level. 

In an inwardly contracted hoof, the bulbs are deformed inwards.




In a shallow hoof that lacks vertical depth at the heel, they may become vertically compressed.

The Frog

The frog is continuous with the digital cushion above it and with the bulbs of the heel.

The frog corium is more like normal dermis than the other coria of the hoof. It produces what should be a tough, leathery pad that can, under certain conditions, degenerate into a soft sometimes, pulpy structure which is easily contused and also easily colonised by pathogens in the ground or in the bedding, if the horse is stabled. (see Canker article)

The frog has two folds in its rearward third and the region between those folds should be a shallow depression. A diseased, weakened frog may lose so much substance in the central sulcus, that the shallow depression becomes a cleft and as such, is a breeding ground for pathogens.

Sometimes, the entire central sulcus degenerates and the frog folds in on itself meaning there is virtually no substance between the top of the cleft and the skin of the pastern.

The photo on the left is of such a hoof; on the right the same hoof a few months later and you can see the extent of the cleft as the hoof has started to open out which allows the central sulcus to regenerate. This heel is still extremely weak and vulnerable to concussive and penetrative injury and infection.

Below - a healthy frog on a soft terrain hoof.

The Digital Cushion

The digital cushion sits above the frog and comprises horizontally arranged bands of fibrocartilage with loose connective tissue in between them. The fibrocartilage attaches to the lateral cartilages and is important in dampening the downward movement of the pastern bones under load and inhibiting the expansion of the heel. 

The DC cannot be seen but the health of it and the frog can be ascertained by placing your thumb on the frog pad in the middle of the central sulcus and your forefinger on the skin of the pastern above the frog, and squeezing. In a healthy hoof this should feel dense and thick and resist the pinch. In a degenerated heel, it feels thin, weak and flabby.  In a severely compressed, underrun and splayed hoof, the thumb and forefinger may almost meet. It is easy to see how inadequate such a structure is to either help dampen the downward load or help inhibit expansion of the heels.

The DC is poorly vascularised and the constant stimulation - from the lateral expansion and return of the heel plus the upward pressure from the ground via the frog pad - is vital for the flow of nutrients that is necessary to maintain cartilage health.  If a horse does not get adequate movement on firm ground in formative years, the digital cushion may never develop properly and will be primarily loose connective tissue.

The Lateral Cartilages

The lateral cartilages with merge with the pedal bone and extend rearward to form the palmar/plantar region. The rear part of the hoof capsule (wall/bars and sole) grows from the laminar and solar corium on the cartilages. They should be dense and strong and curve slightly inwards towards the heel. Without adequate movement and some expansion of the heels, they may be thinner and weaker than is necessary for optimal hoof health.

In a narrow inwardly contracted heel, the LCs are bent inward with the heels; if the hoof is under run, they are pulled under with the heels; if the hoof cannot break over normally the ligamentous attachments of the LCs may be damaged and as a result of long term irritation/damage, they may ossify (side bone).

If the complex of lateral cartilages, fibrocartilaginous DC and dense frog pad is strong and healthy, it not only facilitates the lateral expansion of the heels, it also acts with the bars to control it.

Too little lateral movement reduces shock absorption -> reduces the flow of blood and nutrients ->  reduces tissue and horn health. 

Too much lateral movement or vertical displacement stresses all the structures of the hoof and the coffin and fetlock joints.