Aging By The Teeth

Aging the horse by its teeth is an outdated and inaccurate method.  I no longer recommend this because of today’s abundant methods, including accurate papers and microchips.  The percentage of horses with accurate papers or microchips 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 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 five years):

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

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

This second table (below – Part 2 – after five 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), the 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 erupts and wears away.

6 yearsThe central incisors lose their cups, oval shape, and dental star starting.
7 yearsThe middle incisors lose their cups.
8 yearsThe corner incisors lose their cups.
10 yearsGalvayne’s groove starts at the gum line, dental star full, triangular shape starting.
15 yearsGalvayne’s groove extends from the gum to half the tooth’s length.
20 yearsGalvayne’s groove extends the entire tooth length, all triangle shape.
25 yearsGalvayne’s groove extends from the middle of the tooth to the occlusal edge.
30 yearsGalvayne’s groove disappears, and all have a 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 tongue movement is affected by avoiding the pain created by sharp enamel points of the cheek teeth).  The tongue wears away the incisors and NOT the opposing teeth.

The aging project is pictures of horses with a confirmed date of birth.  With the horse relaxed and without medication, I took four 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 time and a good internet connection.  Open one post at a time and wait for all the images to load entirely before opening another post.

“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.

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

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