As many of us know, the foot is a common source of lameness, up to 90% of lameness can be located below the fetlock. And the heel region of the foot can be blamed for up to 1/3 of chronic lameness. This shouldn’t come as a surprise as the hoof is the part of the body that receives and dampens all the forces generated during ground impact. It is estimated that the hooves bear 2-3 times the weight of the horse at a gallop on a straight line and between 5-10 times the body weight when cornering at a gallop. This means one hoof can hold forces of up to 5000kg for an average sized horse. Therefore the trimming and shoeing of horses is one of the most important influences on the soundness of a horse. Imagine trying to even walk around all day in shoes that are too small or even too big, this is what it is like for a poorly trimmed and shod horse.
A correctly shod horse should have a functional and biomechanically efficient hoof that ensures maximum resilience of the hoof wall. When shoeing a horse, emphasis should be placed on maintaining natural balance, combined with optimum length of toe and correct angulation of the hoof wall relative to the pastern angle. Bare foot trimming is fine for slower gaited, lower level use but basic hoof angle must still be maintained for optimum limb function.
The angle of the hoof capsule and coffin bone should ideally be parallel to the angle of the pastern and the angle of the shoulder. This helps the horse to evenly distribute its weight in the forelimb. If the angle of the hoof is too low, more stress will be put on the structures at the back of the leg including the navicular bone, suspensory ligament, deep and superficial digital flexor tendons. Over time this will lead to degeneration of one or more of these structures. If the angle is too high, an up-right conformation, the fetlock and knee has more strain put on them leading to arthritic changes and problems. Fig 1
Regular hoof care and trimming will also prevent problems occurring and is important to maintain the correct angle of the pastern and the hoof wall. Abnormal hoof–pastern axis greatly contributes to overloading of the heels and chronic heel pain. A normal hoof–pastern axis is one in which a line drawn along the front of the hoof wall is parallel to the pastern. When the toe becomes too long, the hoof wall weakens and the heels become crushed putting strain on the structures at the back of the leg. This changes the break-over of the foot and alters the stride. This conformation is referred to as a broken-back hoof pastern axis and contributes to navicular syndrome, chronic heel pain, coffin joint inflammation, quarter and heel cracks and interference during motion. A high hoof angle creates a broken-forward hoof–pastern axis, where the angle of the hoof wall is higher than the angle of the pastern. This abnormality also contributes to coffin joint inflammation and pain in the navicular area, and to sole bruising. Fig 2
Another important aspect to look at is that the weight-bearing surface of the wall extends as far back as possible. A line drawn from the centre of the cannon bone to the ground should land where the heel ends. Again this is related to toe length and conformation. Fig 3
Break-over is a word commonly used in the horse world. It is the phase of the stride when the horse’s heel lifts off the ground and the time the toe is lifted. During this phase, the toe acts as a pivot point around which the heel rotates. The break-over point is the point where the heel lifts off the ground. Changes in toe length, hoof-pastern axis and hoof angle all affect the break-over. A long toe and low hoof angle will delay break-over as more time and effort is required to rotate the heel over the long lever arm that is the long toe. Trimming the foot to decrease toe length, applying rolled-toed, rocker-toed or square-toed shoes will all facilitate in improving the break-over. Fig 4
Balance can also be assessed by taking radiographs of the feet. This allows us to visualise the coffin bone inside the hoof capsule. Generally two x-rays are taken, one from the side and one from the front. These radiographs can then be used by your vet and your farrier to ensure that your horses foot in the best possible balance for his/her conformation.
We are doing foot balance x-rays at the clinic at a hugely discounted rate (33% off) every Tuesday afternoon for the month of August and September. You will get a print out of the x-rays to take to your farrier and a discussion with an equine vet. Please ring us to book this in.