Again, this is an indication of a past injury that is growing out. Sometimes a horse with feet that are misshapen, or a horse which is landing irregularly to compensate for a lameness in another foot, will show a stain in the part of the foot that has been under the most stress. Often, a semi-circular mark surrounds the point of the frog in overworked horses, or horses working on hard surfaces. It also is a classic sign in the soles of foundered horses. Horses can wear down and damage their soles with excessive pawing, being worked on hard ground or concrete, or by improper shoeing or trimming.
Some horses have fleshy, protruding soles that seem overly sensitive.
These often are flat-footed horses, or horses with underrun heels. A good farrier can help keep the horse comfortable, after making sure that there is no other cause for the sensitivity. It is a semi-circle of tissue that provides a blood supply and growth to the hoof wall. The most common injury to coronets is bruising or scraping of the outer tissue by horses wearing studs on their shoes. Make sure that your horse is protected by bell boots if you work your horse with studs.