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How old is my horse?

Last revised April 25, 2017.

Skull of a young horse. The facing side is cut away to reveal the long roots of the teeth. I3 on the lower side is deciduous; the deciduous I3 on the top has been lost, and the permanent I3 is in the process of growing in, indicating that this horse was about 4.5 years old (see below). One canine is visible. The permanent teeth have long roots, and are ready to continue to grow out from the skull over most of the life of the horse.1

From the Horse’s Mouth

Many methods have been used to estimate the age of a horse. The skin on older horses is less pliable than in younger horses. Their jaw bones are thinner and sharper. Their ribs are farther apart. Their eyes sit deeper in their sockets.2 But their teeth are the best indicator of age.

A horse’s teeth are its greatest ally against hunger. As long as the teeth are working, the horse is able to ingest and make do. But once they wear out, the horse is in trouble. The grass that a horse eats is abrasive — particularly when roots mixed with sand are chewed — and so like most grazing animals, a horse’s teeth extend far into their skulls, and grow during much of their lifetime.

Like most mammals, horses have only two sets of teeth.3 The baby teeth are deciduous, and fall out to be replaced by a second set. An old horse will wish that these permanent teeth really were permanent.

The age of a horse may be fairly accurately inferred from its teeth when it is young. As the horse advances beyond age 5, it is more difficult to be precise in estimates. Estimating a horse’s age from its teeth is a very imprecise business. Studies4 have shown that in many cases, there are large discrepancies between the estimated ages provided by expert clinicians and the actual ages, particularly as a horse ages. When they are young, we estimate a horse’s age from how much their front teeth have grown (and the presence of molars); when they are old, we estimate a horse’s age from how much their teeth have worn.

Our imprecision in dating events increases as the horse grows older, in part due to differences in feed (sandy soil and an overgrazed pasture will cause faster wear than lush forage growing in a clay or loamy soil or stable-fed hay), habit (a horse that cribs or chews its stall or the fence will wear his teeth faster), dental care, and other factors. Haflingers, Lippizzaners and draft horses may have permanent incisors erupting up to six months later than in other horses5, and it has been suggested that enamel hardness and tooth composition differs across breeds, increasing the difficulty of inferring age from tooth wear.6 Comparing a horse who feeds from a hay rack with a horse of the same age who grazes, the former will especially have more youthful incisors. If a horse has had malocclusions or any deformity such as overbite, and has had corrective dental work, inferring age from teeth will be hazardous. And any horse who enjoys chewing his fence or stall will show premature wear of his incisors. I am not recommending keeping horses in stalls or feeding them from hay racks when this can be avoided: grazing may be better than eating from a raised hay rack because the great weight of the lower jaw can relax the temporomandibular joint where it connects to the skull, and wear his teeth evenly through chewing.

All of the teeth in a horse’s mouth have names. All upper teeth have corresponding lower teeth, and the left side should match the right side. Starting at the front are the incisors, then canines, then an optional wolf tooth, then premolars, then molars. A foal will have 24 deciduous teeth: 12 incisors and 12 premolars. An adult will have 36 permanent teeth: 12 incisors, 12 premolars, and 12 molars or perhaps more: add 4 if they have canines, and add 2 if they have wolf teeth.

In a foal, you won’t find canines, wolf teeth, or molars among the deciduous teeth. So if you simply use your finger to feel the gums where the premolars and molars will be found, you can determine the approximate age as follows:

age premolars and molars in arcade
2 weeks – 9 months 3 (all will be premolars)
9-12 months 4 (3 premolars, 1st molar)
1-2 years 5 (3 premolars, 2 molars)
3-4 years 6 (3 premolars, 3 molars)

If you are trying to estimate the age of a horse, you can probably do so most easily by taking a snapshot of the lower incisors. On one side of the bottom, you’ll find I1 (the center-most incisor), I2, and I3 (the outermost incisor). If the horse is likely under the age of 4, then get a good photo of the top surfaces of one set of molars (and premolars) as well. Notes in this section will help you interpret the photos you’ve taken.

Starting from the front center of an adult horse mouth are 3 incisors on each . These are followed by a short toothless gap, and then by a pair of canines (one on each side of the top and of the bottom, for a total of 4 canines). There is then a bank of molars: 3 premolars and 3 molars.

Incisors are the six front top teeth and six front bottom teeth. They are used for cutting, nipping, and gripping the grass during grazing (the grass is pulled into the mouth by the lips, the incisors grasp it, the lips close, and the horse shakes his head, tearing the grass where it is held by the incisors.) The incisors are not involved in chewing. Each incisor on the top has an opposing incisor on the bottom, and each on the left has a counterpart on the right. So the 12 incisors are named “first incisor” (also called the “centrals”), the second incisor (also called the intermediates), and the third incisor (also called the corners). The eruption of the incisors is one of the most reliable methods of estimating age.7

After the corner incisors there is a short gap, and then the horse may have 4 canines (sometimes called the bridle teeth or tusks, and most often found in geldings and stallions. Sometimes a mare will have 1-4 canines).

Another gap — the interdental space — follows, and then there may be small wolf teeth — up to 4 rudimentary teeth in front of the first molars. Sometimes a bitted horse will have the wolf teeth removed if present, to avoid interference with the bit. Ancient horses had more teeth than modern horses, and wolf teeth, if present, may be considered vestigial — they may not help much with grinding food. Between the canines and the wolf teeth, the interdental space is called the bars.

The remaining teeth form an arcade — a row of teeth. The first three are called premolars, and the last 3 are called molars. Together, these 24 teeth (6 on each side of the top, and 6 on each side of the bottom) create a grinding surface. In combination, they may all be called molars or cheek teeth.

Identifying the teeth.8

Uneven wear of teeth can produce hooks — small points on a tooth’s chewing surface — that make chewing difficult. This can be treated by floating the teeth — filing down sharp edges with a long handled rasp or float.9

The cup is a funnel shaped indentation in the center of the surface of a tooth’s enamel and cementum. As with enamel spots and stars, cups are most easily seen when examining the lower incisors of a horse. A horse’s teeth continue to grow throughout much of his life, and as the tooth grows out and wears, the shape of the surface changes. All permanent teeth are cupped when they grow in, but as the tooth continues to grow and wear, the surface characteristics change. Cupping disappears at about 12 years of age, so a horse that shows cupping is likely between 6 or 8 and 12 — or it has been Bishoped. Bishoping is the unethical practice of drilling cups in old incisors, then burning or dying these hollows to resemble youthful cups. Always look a gift horse in the mouth, to try to judge any claims being made of its age, but beware that the horse may have been Bishoped.

Once a cup has disappeared, you will see an enamel spot emerge in its place, at the deepest part of the infundibulum — the place where the cup had been. As the horse continues to age and wear his teeth, a yellow-brown dental star emerges on the top of the pulp cavity, formed from secondary dentin growing in the pulp cavity as the tooth matures. At first, it will be linear in shape, but over time morphs into a large round spot. It remains visible after the cup and enamel spot have been worn away.

Six cross-sections of an incisor from a young horse. The shape and patterning of the biting surface changes over the life of the horse. In the two sections in the upper right of the image, the cup is seen to be shrinking and moving toward the back of the tooth, where it is named “Mark” in the second section from the top. The star is a dark line that emerges in front of the cup, and changes shape as the tooth wears.10

In the image above, an incisor of a horse shows both an enamel spot and a dental star. The spot is in the center of the tooth, and is what remains of the infundibulum. On the outer edge of these incisors, a linear dental star has emerged, revealing the pulp cavity.11

The baby teeth of a young horse (sleeping horse) are short and oval, but longer in an adult (yawning horse).

The incisors of the young horse on the left shows cups. The older horse on the right shows dental stars.12

In the image above right, three lower incisors may be seen, the closest having been cut through vertically. The tooth labeled “Cup” and the one to its right were uncut. The incisor to its left was sliced through vertically where it becomes white. These three teeth are still in the jaw, and the jaw was also sliced through. Because cups may be seen, we know that this horse was between 6 and 12 years old (see chart below). If the sliced tooth had continued to grow and wear, the cup would have shrunk and finally disappeared. The pulp cavity would then have been revealed as a dental star with continued growth and wear, changing in shape over time.13

The shape of the tops of the lower incisors can be useful in aging a horse, because the shape of the surface changes as the horse ages. Horses that are less than 11 have a rounded oval shape. As the horse ages, the tooth continues to grow in response to wear, and the shape shifts from a rounded oval to triangular, and finally rectangular. Older horses will have more tooth showing, having become “long in the tooth.”

The young horse on the left has a vertical tooth profile and less tooth showing. The older horse on the right has more tooth showing, and the incisors are now angled forward.

Galvayne’s groove is a groove that develops in the lateral surface of the upper third incisor. Named by 19th century Australian horse trainer Sydney Galvayne, it starts near the gum line when the horse is about ten years old, and is normally completely gone when the horse reaches the age of 30. Galvayne claimed his method was infallible, but at least one study14 has shown that Galvayne’s groove is nearly useless in predicting a horse’s age. Because of this, I have not included the common claims of the correlation between Galvayne’s groove and horse age in the table below.

In the horse depicted above, the groove is more than halfway from the gumline, and so we could estimate the horse’s age at around 17 or 18.15

Other changes. Teeth change in color, in exposed length, and in smoothness as the horse ages. A young horse will have smooth white teeth, but they become brownish and stained over time. Teeth become more angled over time, too. The upper and lower arcades of molars will consist of nearly vertical teeth when the horse is young, angling forward as the horse ages.

The table below provides an approximate chronology of changes in the horse’s teeth. Some authorities offer somewhat different dates. For instance, the rounded shape of the depression in I1 is replaced with a triangular shape at age 18, according to some authorities,16 at 16 years according to others17. Similarly, some claim I1 becomes round at seven years18, others at 12 years19. And some claim that this tooth becomes triangular at eight years20, while others claim 16 years21.

Date Event
6 (0-7) days I1 (centrals) erupts – D
0-14 days 1st premolar erupts – D
0-14 days 2nd premolar erupts – D
0-14 days 3rd premolar erupts – D
4-6 weeks I2 (intermediates) erupts – D
6-9 months I3 (corners) erupts – D
5-6 months 1st premolar (wolf tooth) erupts – P
9-12 months 1st molar erupts – P
2-5 years Deciduous (baby) teeth replaced by permanent teeth.
2 ½ years 2nd premolar erupts. 1st incisor (centrals) erupts. – P
3 years 3rd premolar erupts – P
3 1/2 years I2 (intermediates) erupts — P
3 ½ to 4 years 3rd molar erupts – P
4 years 4th premolar erupts – P
4 ½ years I3 (corners) erupts – P
4-5 years Canine (bridle) erupts in males and some mares. – P
6 years Cups are gone on I1. Permanent incisors are showing wear in horses (later in mules and donkeys).
7 years Cups are gone on I2
8 years Cups are gone on I3; Stars appear on I1.
9 years Star on I1 is replaced by a rounded shape. Stars appear on I2. Permanent incisors may begin to show wear in donkeys.
10 years Star on I2 is replaced by a rounded shape. Stars appear on I3.
11 years Star on I3 is replaced with a rounded shape.
11 or 12 years Cups have disappeared in horses. (In donkeys, cups may be seen in the lower front teeth until the age of 20). Chewing surfaces on central incisors become round, instead of oval.
14-16 years Corner incisors develop ridges.
16 years Rounded shape of depression in I1 is replaced with a triangular shape.
17 years Rounded shape of depression in I2 is replaced with a triangular shape.
17-18 years Rounded shape of depression in I3 is replaced with a triangular shape.
18-20 years Triangular shape of depression on I1 is replaced with a rectangular shape.
30 years Teeth may begin to fall out.
Over 30 years Teeth are now short. Some are small nubs, some are missing.

Which are the most trustworthy clues to age?

An important study22 measured many of these qualities in photographs of 434 thoroughbreds of known age, and correlated each measured criterion with actual age. Some criteria were fairly good, many were worthless. In all cases, the scatter increased with age.

Here is a summary of the findings in this study.

  • Size and shape of dental star. Correlated between 0.771 and 0.895 (P<0.001).
  • Incisor profile angle: Correlated 0.786 (p<0.001)
  • Change in the size of the infundibulum: Correlated 0.507 to 0.742 (depending on which incisor was measured). (P<0.001). The scatter increased with age.
  • Change in the size of the enamel ring. Enamel rings were found on horses ranging from 9 to 21 years. Ring size correlated with age between 0.700 and 0.834 (P<0.001).
  • Galvayne’s groove: found in horses from four years 11 months to 27 years nine months. Worthless as a tool.

Examples

Here are some photos of teeth, to help us sort through all this material.

Bud’s incisors August 16, 2016. In the photo above, I1 is a permanent tooth, I2 and 3 are smaller, rounded baby teeth. Because his first permanent incisor has erupted, he must be about 2 1/2 or perhaps older, but is less than 3 1/2, when his permanent I2 should erupt. More precision can come from a check of his molars.

Lower incisors and canines in skull from a young horse. Canines are in, so this horse is likely 4-5 years old or more (see table above). Cups in I1 are smaller than the others, but still present, so horse is likely under 6.23

Two lower incisors and canines in skull from an old horse. Canines and incisors are heavily worn, as are the two remaining incisors, suggesting great age. The enamel spot is now triangular in shape, suggesting an age of 17-18 or more. Four incisors are missing, which could have happened before or after the horse died, but if any were lost before, the horse might have been as much as 30 at the time of death.

 

Dental disease can affect behavior. Common symptoms in a standing horse include loss of food when chewing, inefficient chewing, excessive salivation, foul odor coming from the mouth or nostrils, a head that is held tilted, head shaking, sensitive cheeks, blood in the mouth, weight loss or rough hair. When a horse with dental problems is ridden, it may show abnormal sensitivity to the bit or brace against it, head throwing, tail ringing, odd head carriage, or refusal to respond to the bit for stops and turns.24

Your horse should have a dental checkup at regular intervals, and whenever any symptoms such as those in the above paragraph suggest dental problems. The checkup will likely include sedation so that teeth can be floated, removing any sharp points that have developed. Horses under 4, over 25, or with any dental abnormalities may benefit from twice yearly dental care.

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1 “Antique Real Horse Skull Veterinary Medicine Victorian Taxidermy Oddity Art” EBay. http://www.ebay.com/itm/ANTIQUE-Real-Horse-Skull-Veterinary-Medicine-Victorian-Taxidermy-Oddity-Art-RARE-/231170118787

2 Smith, K. “Judging Horse Age from Teeth” http://equusmagazine.com/article/eqteeth2503-8261

3 Elephants go through six sets of teeth, replacing each set with the next as the old set is worn out. When the last set is worn out, the elephant must starve to death, though few elephants survive poaching this long these days.

4 Richardson, J. D., Cripps, P. J., Hillyer, M. H., O’Brien, J. K., Pinsent, P. J., & Lane, J. G. (1995). An evaluation of the accuracy of ageing horses by their dentition: a matter of experience?. The Veterinary Record137(4), 88-90.; Richardson, J. D., Cripps, P. J., & Lane, J. G. (1995). An evaluation of the accuracy of ageing horses by their dentition: changes of dental morphology with age. Veterinary record137, 117-117.

5 Eisenmenger, E., & Zetner, K. (1985). Veterinary Dentistry. Philadelphia. Lea & Febiger, pp 14, 48.

6 Smith, K. “Judging Horse Age from Teeth” http://equusmagazine.com/article/eqteeth2503-8261

7 Richardson, J. D., Cripps, P. J., & Lane, J. G. (1995). An evaluation of the accuracy of ageing horses by their dentition: changes of dental morphology with age. Veterinary record137, 117-117.

8 Crowe, D. “Students get a lesson in horse dentistry” Rocky Mountain Collegian. September 17, 2014 http://collegian.com/2014/09/students-get-lesson-horse-dentistry/89482/

9 I’ve invented a powered equine reciprocating float, described here: http://davidstang.com/?p=915

10 image from Hadrill, D. “Horse Healthcare – A Manual for Animal Health Workers and Owners” 2002. 256 pp. ITDG Publishing. ISBN: 1 85339 486 6

http://fastonline.org/CD3WD_40/LSTOCK/001/ITProv_May_2005/h4340e%20Horse%20Healthcare/h4340e.20.htm (c) David Hadrill.

11 Photo source: Rouge, M. “Aging Horses by their Teeth”. Colorado State University. http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/aginghorses.html

12 Image source: Rouge, M. “Aging Horses by Their Teeth” http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/aginghorses.html

13 Photo source: Rouge, M. “Aging Horses by their Teeth”. Colorado State University. http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/aginghorses.html

14 Richardson, J. D., Cripps, P. J., & Lane, J. G. (1995). An evaluation of the accuracy of ageing horses by their dentition: changes of dental morphology with age. Veterinary record137, 117-117.

15 Image source: Rouge, M. “Aging Horses by Their Teeth” http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/aginghorses.html

16 Cleveland, C. “Horse Teeth – Age, Anatomy and Growth” http://www.equinespot.com/horse-teeth.html

17 Rouge, M. “Aging Horses by Their Teeth” http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/aginghorses.html

18 Tutt, J.F.D. (1968) Captain M. Horace Hayes’ Veterinary Notes for Horse Owners. 15th edition. London, Stanley Paul, p. 512.

19 Eisenmenger, E., & K. Zetner. (1985). Veterinary Dentistry. Philadelphia. Lea & FEbiger, pp. 14, 48.

20 Brown, G.T. (1882). Journal of the Royal Agricultural Society of England. 2nd Series, 18, 390.

21 Montes, G.S. (1978) Gaceta Veterinaria 40, 333, 565.

22 Richardson, J. D., Cripps, P. J., & Lane, J. G. (1995). An evaluation of the accuracy of ageing horses by their dentition: changes of dental morphology with age. Veterinary record, 137, 117-117.

23 Image source: David Stang

24 Easley, J. “Equine Teeth” http://www.sportpolo.com/barn/Equine_Teeth.htm

 

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