The Horse’s HoofBy Dr. Peter Huntington · August 31, 2011
The old saying “no foot, no horse” still holds true. Without healthy hooves, the horse is uncomfortable and unable to train or work. In order to provide correct care for the horse’s hooves, owners need to have an understanding of their construction.
The wall of the hoof grows from the coronary band at the rate of 6–9 mm (¼ to ½ inch) per month. As the average hoof is 76–100 mm (2½ to 4 inches) long at the toe, this means that the horse grows a new hoof in about a year. The hoof wall is made of a tough material called keratin that has a low moisture content (approximately 25% water), making it very hard and rough. The wall has three layers: the outer periople, a middle layer, and an inner layer. The periople extends almost 19–25 mm (¾ to 1 inch) at the top of the wall to protect the sensitive coronary band at the junction of the skin and the hoof. It is very tough and of a similar consistency to the frog. After extending nearly 20 mm (¾ inch), the periople changes into a thin layer of material that covers the rest of the hoof and gives it a shiny appearance, acting as a protective covering. It helps to control evaporation of moisture from the wall. The middle layer makes up the bulk of the wall and is responsible for its strength and rigidity. The inner layer forms the insensitive (horny) laminae of the hoof, which mesh with the sensitive laminae that cover the pedal bone (third phalanx or coffin bone) and firmly attach it to the wall of the hoof. In general, the main function of the wall is to bear weight. It must be trimmed at regular intervals to keep it properly shaped and level. When a horse is shod, the nails of the shoe are driven up into and through the wall. The heel is the most elastic part of the hoof, allowing the hoof to expand during movement. Because the heel is somewhat softer than the toe, care must be taken when trimming it.
The white line is the junction of the wall and the sole. It is a guide for placing the horseshoe nails to be driven into the hoof. Nails should be placed so that they pass through the hoof wall edge of the white line. They may penetrate the sensitive structures in the hoof if they are placed closer to the sole. The hoof can sometimes split along the white line, a condition called seedy toe that can allow an infection to develop in the hoof.
The sole makes up most of the undersurface of the hoof. It is made up of nearly 33% water, so it is softer than the wall. The structure of the sole is similar to that of the wall, except that it breaks away when it grows to a certain thickness. The sole is thickest at its junction with the wall and should be concave in shape, which gives the horse more traction. The sole of the hind foot is normally more concave than that of the front foot. The function of the sole is to protect the sensitive structures within the hoof. It must be protected from constant pressure, as bruising and lameness may result if the sole is hitting the ground.
The bars are the parts of the wall that have turned inward from the heels to surround the frog. Their function is to bear weight.
The frog is wedge-shaped and made of rubbery and highly elastic material that is 50% moisture. The frog is a shock absorber in its own right, and it also distributes concussion to the internal digital cushion. The frog provides traction and helps to prevent slipping, and is also an aid to blood circulation and heel expansion because of its position between the bars of the hoof. The frog should not be trimmed, except to remove flaking pieces after trimming the rest of the hoof. The frog should be level with the ground surface of the walls of the heels.
The coronary band is the primary source of growth and nutrition for most of the hoof wall. Injuries to this structure are serious and usually leave a permanent defect in the wall as it grows.
Laminar corium (sensitive laminae)
The laminar corium consists of laminae engorged with blood vessels. The sensitive laminae mesh with the insensitive laminae of the wall on one side, and are firmly attached to the pedal bone on the other side. This bond with the insensitive laminae is disrupted during laminitis.
Solar corium (sensitive sole)
The solar corium consists of hair-like laminae swollen with blood vessels. These laminae mesh with the insensitive laminae of the sole and frog to supply nourishment for growth.
The digital cushion is a tough, elastic, fatty, yielding structure sitting on top of the frog and behind the pedal bone. It is visible externally as the bulbs of the heels. Its main function is to reduce concussion to the foot, as well as circulating blood back up the foot by acting as a pump when it compresses veins against the lateral cartilages. It also aids heel expansion.
The lateral cartilages slope upward and backward from the wings of the pedal bone and reach the margin of the coronary band, where they can be felt near the heels. The many veins on the internal sides of the lateral cartilages are compressed against the cartilage when weight is placed on the foot. This mechanism forces the venous blood back to the heart. When weight is taken off the foot, compression of the veins is released and the veins refill with blood. The disease called sidebone occurs if the lateral cartilages turn into bone.
Bones of the hoof
Two bones are completely within the hoof. The pedal bone (also known as the distal phalanx, P3 or coffin bone) is the largest and is shaped like the hoof. The significantly smaller, shuttle-shaped navicular bone lies adjacent to the pedal bone and closer to the heel.
The hoof is a complex grouping of sensitive and insensitive structures, all of which must be kept healthy and undamaged if the horse is to stay sound. Good nutritional management and regular farrier care will help to ensure strong hooves.
This article is adapted, with permission, from Horse Sense—The Guide to Horse Care in Australia and New Zealand, second edition (2004).