Ageing by teeth is one of the oldest skills in horsemanship and it is still genuinely useful — but it has become less necessary and more misunderstood at the same time. In the UK the passport records a date of birth, so teeth are usually a cross-check rather than the primary source. Where they matter is when the paperwork is missing, vague, or does not match the animal.
Which teeth are we looking at?
The six upper and six lower incisors at the front of the mouth. From the middle outwards they are called centrals, middles and corners. Everything below concerns those twelve teeth; the molars matter enormously for the horse's health but are not used for ageing in the field.
Eruption: birth to five years
This is the reliable phase. Eruption times are consistent enough that a vet can age a young horse to within a few months.
| Age | What appears |
|---|---|
| Birth to 1 week | Deciduous (milk) central incisors |
| 4–6 weeks | Deciduous middles |
| 6–9 months | Deciduous corners — full set of milk teeth |
| 2½ years | Permanent centrals replace the milk centrals |
| 3½ years | Permanent middles |
| 4½ years | Permanent corners |
| 5 years | Full mouth — all permanent incisors in wear |
Permanent incisors are larger, squarer and more yellow than the small, white, shovel-shaped milk teeth. The commonest mistake is calling a four-year-old a five-year-old because the corners have erupted but are not yet in wear — the corner teeth must be meeting their opposite number, not merely visible.
Cups and the dental star: six to twelve years
A cup is the dark hollow in the centre of the biting surface of a young permanent incisor. As the tooth wears down, the cup disappears — and it does so in a fairly predictable order in the lower incisors: centrals at about 6, middles at about 7, corners at about 8. The old phrase for a horse that has worn all its lower cups away is "past mark of mouth".
As the cup goes, the dental star appears: a line, then an oval, then a round mark in front of where the cup was. Its shape helps refine the estimate through the horse's teens. The uppers wear on the same pattern, roughly three years behind the lowers — 9, 10 and 11.
Galvayne's groove: ten to thirty
A dark groove that appears at the gum line of the upper corner incisor and grows downwards as the tooth erupts over time. The conventional milestones:
- About 10 years — the groove appears at the gum.
- About 15 years — it has grown halfway down the tooth.
- About 20 years — it runs the full length.
- About 25 years — the top half has worn away, leaving it on the lower half only.
- About 30 years — it has gone entirely.
It is a useful marker and a famously unreliable one. Plenty of horses have a faint groove, an irregular one, or none at all. Use it to support an estimate, never to make one on its own.
Hooks, angle and shape
- The 7-year hook: a notch on the back edge of the upper corner incisor, appearing around 7 and usually worn away by 9.
- The 11-year hook: often reappears around 11 to 13.
- Angle of incidence: seen from the side, the incisors of a young horse meet almost vertically. With age the angle becomes progressively more acute and the teeth appear to slope forwards — one of the more reliable impressions of an aged mouth.
- Shape of the biting surface: oval in a young horse, becoming round in middle age, then triangular, then rectangular from front to back in old age.
How accurate is it really?
| Horse's age | How close an experienced vet can get |
|---|---|
| Under 5 | Within a few months |
| 5–10 | Within about a year |
| 10–15 | Within one to two years |
| 15–20 | Within two to four years |
| Over 20 | An estimate only, often ±5 years |
Wear is affected by diet, by grazing on sandy or abrasive ground, by crib-biting, which wears the incisors abnormally, and by conformational faults such as parrot mouth. Any of these can shift an estimate by years.
What should a buyer actually do?
- Read the passport or registration papers and note the stated date of birth.
- Ask the vet doing the pre-purchase exam to age the horse from its teeth as part of the examination — it is a standard part of stage one and costs nothing extra.
- Compare the two. A one- or two-year discrepancy in a horse in its teens is unremarkable. A five-year gap, or a mouth that does not match the paperwork at all, is a serious question about identity.
- Have the microchip scanned and matched to the passport at the same visit. Together, chip and teeth close almost every route to selling one horse as another.