Horses' teeth are often used to estimate the animal's age, hence the saying "Don't look a gift horse in the mouth".

At five years of age a horse has forty teeth:

  • twenty-four molarss or jaw teeth
  • twelve incisors or front teeth
  • four tusks or canine teeth between the molars and incisors; these are generally found in all horses but sometimes fail to erupt and remain in the jaw. An old wives tale thought that only colts (and therefor stallions and geldings) had them but this is not true.

Some horses also have wolf teeth - a throwback to the old fighting tooth. If present these can cause problems in the bitting of the horse as they are where the bit sits.

At birth only the two nippers or middle incisors appear.

At one year old all the incisors of the first or milk set of teeth are visible.

Before three years, the permanent nippers have come through.

At four years old, the permanent dividers next to the nippers have emerged.

At five the mouth is perfect, the second set of teeth having been completed.

At six the hollow under the nippers, called the mark, has disappeared from the nippers, and diminished in the dividers.

At seven the mark has disappeared from the dividers, and the next teeth, or corners, are level, though showing the mark.

At eight the mark has gone from the corners and the horse is said to be aged. After this time, indeed good authorities say after five years, the age of a horse can only be conjectured. But the teeth gradually change their form, the incisors becoming round, oval, and then triangular. Dishonest dealers sometimes "bishop" the teeth of old horses, that is scoop them out, to imitate the mark: but this can be known by the absence of the white edge of enamel which always surrounds the real mark, by the shape of the teeth, and other marks of age about the animal.