The saying "long in the tooth" comes directly from horses — as a horse ages, its teeth continue to erupt and wear in predictable patterns, giving experienced observers a rough way to estimate age when records aren't available.
Young Horses
Foals are typically born without visible teeth, and baby teeth erupt and are gradually replaced by permanent teeth between roughly 2 and 5 years of age — the clearest and most reliable window for age estimation.
Adult Horses
Past the age of 5, estimating age relies on more subtle cues: the angle at which the teeth meet, changes in shape from round to triangular, and the appearance of certain grooves (like "Galvayne's groove") that develop later in life.
Galvayne's groove, a dark line that appears on the upper corner incisor around age 10 and gradually grows down and then out of the tooth, is a classic (if imperfect) aging landmark.
Limits of This Method
Diet, genetics, and cribbing habits can all affect tooth wear, so aging by teeth becomes an estimate rather than an exact science past a horse's early years — always considered alongside other records when available.
← Back to Horse Health