The equine foot is made up of complex external and internal structures designed to adapt to varying terrains and environmental conditions whilst withstanding tremendous forces. Our vet Rebekah McFarling explains here why it is vital that the horse’s feet are kept in good condition and balance, with correct care, regular trimming and, if required, shoeing.
The pedal bone
One of the most important structures within the horse’s foot is the pedal bone, a triangular shaped bone which is connected to the hoof capsule by a sling of fibres called laminae. The entire weight of the horse is held up through this framework so it must withstand the considerable forces exerted at each pace:
- At walk, the force through each foot is 0.5 x bodyweight of the horse
- At trot, force = 1 x bodyweight
- At gallop, force = 2.5 x bodyweight. For most horses this over a tonne!
Any alterations to the angle of the pedal bone, the hoof structure or the integrity of the laminae can have detrimental effects.
In order to accurately assess foot balance, we need to be able to visualise the pedal bone. This can be achieved by your vet obtaining radiographs of your horse’s feet, which can then be used to make recommendations regarding trimming and/or shoeing.
Lameness and poor foot balance
Foot balance relates to both the medio-lateral (side to side) and cranio-caudal (front to back) angles of the pedal bone within the hoof capsule. The palmar angle is the angle between the bottom of the pedal bone and the ground, which should be slightly positive, where the back of the pedal bone is slightly higher than the front. A negative palmar angle may be seen in cases with collapsed heels, or in horses that have a loss of structure of the digital cushion.
Indications of poor foot balance include long toes and low heels (particularly seen in thoroughbreds), flared quarters, cracks in the hooves and diverging hoof rings. An example of a horse with a long toe is shown in the main image.
Lameness is frequently caused by poor foot balance as structures such as joints, tendons and ligaments are all affected by alterations in the angle of the foot. The deep digital flexor tendon (DDFT), originating at the humerus, runs all the way down the back of the leg into the foot, passing over the navicular bone before inserting onto the pedal bone. A one degree decrease to the slope of the solar surface of the foot (a longer toe increases the slope), can increase the strain on the DDFT by 4%, risking not only damage to this structure, but also to the navicular bone, with which it is in contact.
Laminitis
In a normal foot, the pedal bone should be in line with the coronary band and parallel to the dorsal hoof wall. In laminitis, the laminae become weakened and disrupted so they can no longer support the weight of the horse. This can result in 2 scenarios:
- The pedal bone rotates downwards, so the tip of the pedal bone points down towards the sole. This means the pedal bone is no longer parallel to the dorsal hoof wall.
- The pedal bone sinks downward so that it is no longer in line with the coronary band.
Horses with chronic laminitis may experience both rotation and sinking of the pedal bone, which often results in changes in hoof conformation, laminitic growth rings and stretching of the white line. Any change to the pedal bone from laminitis is painful and this causes lameness. Most commonly this is seen in both forefeet but can be in the hind feet or just one foot.
In severe cases of laminitis, the pedal bone can eventually collapse through the sole of the foot; this is extremely painful and cannot be reversed.
If you suspect your horse/pony has laminitis, you should seek immediate advice from your vet.
Summary
Your farrier plays a vital role in achieving good foot balance by correct trimming your horse’s hooves to maintain correct alignment of the pedal bone, or to realign it. For horses that are shod, appropriate shoe selection and placement on the foot is equally important.
Radiographs taken by your vet are a very useful tool to provide visualisation of the internal structures of the hoof capsule as well as to make recommendations regarding farriery, and to monitor changes over time.