Introduction To Aging The Horse By Their Teeth

Aging the horse by their teeth is an outdated and inaccurate method.  I no longer recommend this because of the abundant methods available today including accurate papers and microchips.  This said, the percent of horses with accurate papers or a microchip is low so the teeth method is still widely used.

Aging the horse by the teeth uses the regular wear of the incisors.  The theory is that as the horse ages, the incisor teeth will wear at a uniform (over time) and even (within the mouth on each side) rate.  In college I memorized this chart (below) but over time I soon realized that the rate of wear was not uniform over time between equally aged horses or within the individual horse when comparing the left and right sides.

Here is the chart I memorized (Part 1 – the first 5 years):

6 days old The central incisors appear.
6 weeks old The middle incisors appear.
6 months old The corner incisors appear.
2 1/2 years The central incisor caps are lost.
3 years The first cheek teeth caps are lost and the 4th cheek teeth erupt.
3 1/2 years The middle incisor caps are lost.
4 years The second cheek teeth caps are lost and the 5th cheek teeth erupt.
4 1/2 years The corner incisor caps are lost.
4 – 5 years The 3rd cheek teeth caps are lost and the last cheek teeth erupt.
6 months time All permanent incisors take 6 months from eruption to being in wear.

“Full mouth at 5 years.”  This is a fairly accurate expression although the corner incisor caps sometimes shed later than 5 years.  Most of the incisor observations are close although any delay in eruption or deviation in projection of the permanent incisors will affect the accuracy.  An abnormal mouth confirmation will also change the wear and hence affect the aging, for example parrot mouth, wry mouth, sow mouth or trauma to the incisors.

This second table (below – Part 2 – after 5 years) looks at the cups (the hollow “cup” formation in the center of the occlusal surface of the lower incisors), the dental star (a dark spot between the tongue side and the cup), te shape of the occlusal surface and a groove (Galvayne’s groove) that runs the length of the upper corner incisor over time.  It is a static groove relative to the tooth itself but appears to move relative to the gum line and the occlusal edge as the tooth both erupts and wears away.

6 years The central incisors lose their cups, oval shape, dental star starting.
7 years The middle incisors lose their cups.
8 years The corner incisors loose their cups.
10 years Galvayne’s groove starts at the gum line, dental star full, triangular shape starting.
15 years Galvayne’s groove extends from the gum to half the length of the tooth.
20 years Galvayne’s groove extends the full the length of the tooth, all triangle shape.
25 years Galvayne’s groove extends from the middle of the tooth to the occlusal edge.
30 years Galvayne’s groove disappears, all round shape.

The factors that affect the wear of the incisors are:

  • the type of tooth enamel (Type 1 is soft and is predominantly in the incisors whereas type 2 is predominantly in the cheek teeth are type 2.  There is type 3 which I call brittle).
  • the amount they chew per day (the range is between 10,000 and 40,000 chews per day)
  • the movement of the chewing (horses predominantly chew in one circular direction poorly described as clockwise or counterclockwise just as we are left or right handed dominant)
  • the movement of the tongue affected by avoiding the pain created from sharp enamel points of the cheek teeth).  It is the tongue that wears away the incisors and NOT the opposing teeth.

The aging project are pictures of horses with a confirmed date of birth.  With the horse relaxed and without medication, I took 4 views of the incisors: left side, right side, straight on and open mouth to see the occlusal surfaces of the lower incisors (cups, shape).

Viewing these aging project posts will take some time and a good internet connection.  Open 1 post at a time and wait for all the images to fully load before opening another post.

My conclusion from the project is to lump horses into 5 groups of ages:

  • Young 2-5
  • Young Adult 6-12
  • Adult 13-18
  • Young Senior 19-24
  • Senior 25+

“Age is the number of times the sun has been circled, but how old you are is how you feel in your mind and heart.” – Doc T

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Aging Horses By Their Teeth – Young Horses (2 – 5 years)

Young horses range in age from birth to 5 years. These images are by year 2 through 5. Each show the left side, the right side, the straight on and the open mouth / occlusal surface of the lower incisors. Comparison can be made for individual variations within each age group.

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Aging Horses By Their Teeth – Adult Horses (13 – 18 years)

Young adult horses range in age from 13 to 18 years. These images are by year 13 through 18. Each show the left side, the right side, the straight on and the open mouth / occlusal surface of the lower incisors. Comparison can be made for individual variations within each age group.

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