Aging horses by their incisor teeth is as much an art as a science. Traditional “indicators of age,” such as eruption date, “cups,” Galvayne’s groove, hooks, shape of the table surface of the lower central incisors, etc., often result in wide age estimates. The authors believe that accuracy can be improved by first placing horses less than 20 years old into one of four age groups before applying the traditional indicator. Then by using a systematic approach and applying the following concepts, the age of most horses can be accurately estimated.

Important Concepts

• Horses under 20 are placed into one of four age groups by examining a single tooth, the upper corner incisor (UCI).
• All traditional “indicators of age” can be used, but eruption dates, “cups,” Galvayne’s groove, and the table surface shape of the lower central incisors are most reliable.
• When examining horses under five years, the examiner should be aware that time of year is very important since horses shed their teeth in the fall. For example, a three-year-old’s teeth will look much different in February than they will in November. However, not all horses follow that rule, which can cause confusion when determining the true age of the horse.
• Most horses are born in the spring, and all Thoroughbreds have an “official” birthday on Jan. 1.
• “Atypical” horses do occur and can usually be recognized when their age group and indicators do not match, resulting in wide age range estimates.

Age Categories

Under five years—This age group has a deciduous (baby) UCI from eight months to about four years. Eruption time of the central, middle, and corner incisors (approximately two, three, and four years) are the primary source of information in this age group and are considered highly accurate in the general population.

Five to nine—UCI is now a permanent tooth and should be wider than it is tall (five to six years) progressing toward square (nine to 10 years). Younger horses in this age group should have “cups” on the table surface of the lower incisors. These cups will be gone from the central incisors once the horse turns six years old, gone from the middle incisors by age seven, and gone from the corner incisors at the age of eight or nine. The table surface of the lower central incisor should be oval from side-to-side in this age group.

Ten to 14—The UCI should be square (nine to 10 years) or taller than wide (12-14 years). Galvayne’s groove should start to appear at the gum line when the horse is 10 years old and progress to halfway down the UCI by the age of 15. The table surface of the lower central incisor should be round to triangular