How to age a horse by its teeth (and why it's only an estimate)

Looking in a horse's mouth is the traditional way to estimate age when there are no papers, and it's a skill tested in Pony Club Australia's higher certificates (PCA Syllabus). It's useful – but it's an estimate, not a birth certificate. This guide explains what changes in the teeth with age, and what research says about how accurate those changes really are.

Only look in a horse's mouth if you're confident handling horses, and have someone experienced hold the horse. Never put your fingers between the back teeth.

Know the teeth you're looking at

Ageing mostly uses the incisors – the 12 front biting teeth, six on top and six below. In each jaw they're grouped into pairs:

• Centrals – the middle two
• Intermediates – either side of the centrals
• Corners – the outermost pair

Male horses usually also have canine teeth (tushes) in the gap between the incisors and cheek teeth. Mares sometimes have small ones. Canines usually appear at about 4 to 5 years (Utah State University Extension). Don't confuse them with wolf teeth – small teeth just in front of the cheek teeth, which are often removed because they can interfere with the bit.

For a broader look at the mouth and dental care, see horse dental care.

Birth to 5 years: milk teeth and permanent teeth

Young horses are the easiest to age, because baby (milk or deciduous) teeth are replaced by permanent teeth on a fairly predictable timetable.

Milk teeth in foals

Utah State University Extension describes a handy rule of thumb – milk incisors come through at roughly 8 days, 8 weeks and 8 months for the centrals, intermediates and corners (USU Extension). Its eruption table puts the ranges at:

• Centrals: birth or first week
• Intermediates: 4–6 weeks
• Corners: 6–9 months

Milk teeth are smaller, whiter and have a clear "neck" where they meet the gum.

Permanent incisors

Permanent incisors push out the milk teeth at about (USU Extension):

Tooth	Comes through at about
Centrals	2½ years
Intermediates	3½ years
Corners	4½ years

USU describes a horse as having a "full mouth" at about 5 years, when all permanent teeth are through and in wear.

6 to about 12 years: cups and stars

After 5, age is judged from wear on the biting surface (the "table") of the incisors.

Cups

A young permanent incisor has a dark, indented cup in the centre of its biting surface. As the tooth wears, the cup disappears. USU gives these average ages for cups disappearing (USU Extension):

• Lower incisors: centrals at about 6, intermediates at 7, corners at 8
• Upper incisors: centrals at about 9, intermediates at 10, corners at 11

A horse with no cups left is called smooth-mouthed, usually 12 or older.

Dental star

As the cup wears away, a yellowish-brown mark called the dental star appears closer to the lip side of the tooth. USU says it shows on the centrals at about 8, intermediates at 9 and corners at 10. It starts as a narrow line and becomes rounder and more central with age (USU Extension).

Older horses: shape and angle

Shape of the biting surface

According to USU, the biting surface of the incisors changes shape over time (USU Extension):

• Under about 9: wide and oval-to-rectangular, side to side
• About 9 to mid-teens: rounder
• Late teens and older: triangular

Angle and length

From the side, young horses' incisors meet fairly upright. With age, the teeth slope forward more and more tooth shows below the gum – the origin of the phrase "long in the tooth" (USU Extension).

Galvayne's groove and the 7-year hook

Two features are often taught, but are best treated with caution.

Galvayne's groove

A dark groove on the outer surface of the upper corner incisor. The traditional timetable, as summarised by USU, has it appearing at the gum at about 10, reaching halfway down at 15, running the full length at 20, growing out from the top by 25, and gone by about 30 (USU Extension).

The hook

A small hook can form on the back edge of the upper corner incisor. USU describes it appearing around 7, disappearing, and often reappearing around 11 (USU Extension).

What the research says

A University of Bristol study photographed the teeth of 434 Thoroughbreds of known age. It found that incisor eruption was the most consistent feature, but still not totally reliable. Galvayne's groove and the upper corner hook were of no value for estimating age, and the dental star had the strongest link to age among the wear features. The authors concluded that, because horses vary so much, ageing by teeth can never be precise (Richardson et al., Veterinary Record, 1995). A companion study looked at how accurately vets estimated age from teeth (Veterinary Record, 1995).

USU also notes that diet and behaviour affect wear – for example, crib-biting can wear down the upper incisors (USU Extension).

How to look: a simple routine

1. Have the horse held in a headcollar by an experienced handler.
2. Part the lips at the front, gently, with the horse's mouth closed, to see the incisors from the front and side. Look at the angle and how much tooth shows.
3. Count permanent and milk teeth in a young horse.
4. Look at the tables. Gently hold the upper lip and lower lip apart to see the biting surfaces. Note cups, stars and shape.
5. Check the upper corner incisor from the side.
6. Put it together and give an age range, not a single number.

Why age matters for care

Age guides decisions about feeding, dental care, vaccination and workload. Victoria's Code of Practice for the Welfare of Horses considers a horse aged at 20, and recommends aged and geriatric horses have a general health check and full dental examination every 12 months (Code of Practice). The Code also recommends that all horses' teeth be checked at least once a year by someone skilled in equine dentistry, and more often for young, stable-fed and aged horses. See older horse care.

If you're buying a horse with an uncertain age, a vet can estimate age as part of a pre-purchase examination – see buying a horse. Registered horses may have papers, and microchip or brand records can help confirm identity.

Find an equine dentist near you on horse.work, or an equine vet for a dental and age assessment.

FAQ

How accurate is ageing a horse by its teeth?

It's an estimate. Research on 434 horses of known age found that specific ages can't be assigned to dental features because horses vary so widely (Veterinary Record, 1995). It's most reliable in young horses, while teeth are erupting.

At what age does a horse have a full mouth?

About 5 years, when all permanent teeth have erupted and are in wear (USU Extension).

What does "smooth-mouthed" mean?

A horse whose incisor cups have all worn away, usually about 12 or older (USU Extension).

Is Galvayne's groove reliable?

Not very. A study of horses of known age found it had no value for estimating age (Veterinary Record, 1995).

How often should a horse's teeth be checked?

At least once a year, and more often for young, stable-fed and older horses (Code of Practice). The BHS also recommends at least yearly checks to prevent sharp points (BHS).