1. Millions of years ago, the ancestors of the modern horse had three or four functional toes. But through evolution, some equid ancestors lost their side toes and developed a single hoof. While only horses with single-toed hooves survive today, the remains of tiny vestigial toes can still be found on the bones above their hooves. The splint bone is formed of two of these former toes, the second and fourth toe. The third, or middle, toe is the cannon bone.
2. Recent research suggests that, while modern horses are still partially genetically “programmed” to create five toes in each foot, those four extra toes either don’t develop fully or essentially disappear during fetal development.
3. The wall of the hoof grows from the coronary band at the rate of 6-9mm (¼ to ½ inch) per month. As the average hoof is 76-100mm (2½ to 4 inches) long at the toe, this means that the horse grows a new hoof in about a year.
4. The wall, bars and frog are all weight-bearing structures of the foot and should contact the ground when the horse is standing or moving. The bars are the parts of the wall that have turned inward from the heels to surround the frog.
5. No one knows for sure why the frog is called the frog. Most sources suggest the word derives from the Italian or French word for fork, forchetta and fourchette, respectively. Remember that early forks had only two tines. If you squint, a freshly trimmed frog does look a bit fork-like.
6. The rubbery 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.
7. The digital cushion is a fibro-elastic, fatty, pale yellow pyramidal structure containing cartilage and is located in the posterior (back) half of the foot. Its primary purpose is to reduce concussion to the internal structures.
8. Also found inside the hoof is the coffin bone, also known as the pedal bone or distal phalanx, third phalanx or P3. It is the bottommost bone in the equine leg and is encased by the hoof capsule. The coffin bone is connected to the inner wall by a structure called the laminar layer. The insensitive laminae coming in from the hoof wall connects to the sensitive laminae layer, containing the blood supply and nerves, which is attached to the coffin bone. The lamina is a critical structure for hoof health, therefore any injury to the hoof or its support system can in turn affect the coffin bone.
9. If you feel the heels of the horse you should detect the resistant but (hopefully!) flexible lateral cartilages on each side. The lateral cartilages slope upward and backward from the wings of the coffin bone. 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.
10. The hoof wall is made of a tough material called keratin that has a low moisture content, making it very hard and durable. Keratin is the toughest biological tissue and forms the beaks and claws of birds, the shells of tortoises and the outer sheath of the horns of mammals like the pronghorn or bison. So, they really don’t feel it when they step on your toe.