There are many reports and charts that show how the horse wears their incisors at a uniform rate. Over time this constant wear reveals structures that appear at a predictable age. The thought is that by identifying specific features on the incisors, the age of the horse could be determined.
For example, the cups seen on the occlusal surface of the middle lower incisor is worn away at 6 years of age. Another example would be the development of a groove on the upper corner incisor starting at 10 years of age.
The dates associated with the appearance or disappearance of these structures were memorized by countless horsemen and horse professionals including me as an undergraduate at Cornell. However, as I worked on the teeth of tens of thousands of horses I found that these "rules" were not only inaccurate when compared with the registration papers, but often there would be a difference of 5 years in markings seen between the left side and the right side of the same horse.
I decided to do my own study which several other veterinarians had done in the past to debunk the theory that the age of a horse could be determined by the wear of the incisors.
The Aging Project
I photographed 4 views of the incisors of horses aged from 2 years old to 30+ years old. These views included the left and right sides, the straight on view, and the occlusal surface of the lower incisors.
I selected at random horses in my practice that were either clearly tattooed or the owner had papers for the horse. My goal was to have 10 horses in each age. This would be 10 horses x 4 views = 40 views per age. Multiply this with 29 age groups and that yields 1160 photographs. However, I was unable to find all the horses I wanted. The ages 17, 26, and 29 had few representatives and several other ages had half or less than my goal of 10 horses. My final count was 878 photographs which when divided by 29 ages equals on average 30 images per age.
The images are divided into 2 basic groups:
- All the teeth of one view in chronological order. As the horse ages, you can see some general changes but within the group there are variations and not a clear path of an organized change that a accurate age could be determined from.
- All teeth from one age group with each view organized to compare identifying marks within one age.
1) There is no accurate correlation between identifying marks on the incisors and the age of the horse. 2) The age of the horse can be placed into 5 groups, though the line separating these groups is blurry:
- young 2-5 yr
- young adult 6-12 yr
- adult 13-18 yr
- early senior 19-24 yr
- senior 25-30+ yr
3) The tongue rests firmly behind the incisors and fills all the space. It becomes clear that:
- The tongue shapes the canine teeth into a dagger like object with 2 sharp edges and a point.
- The tongue pushes the incisors forward so that older horses have more of an angle away from vertical than younger horses.
- The tongue in most horses rests between the incisors in a relaxed horse (see the straight in view). Therefore in the resting horse, none of the teeth (cheek or incisors) are in occlusion. These images are not capturing the horse in the middle of opening their mouths but rather they represent the normal relaxed state of the horse (non-chewing).
Please visit the new home of the aging project here (new tab) at The Horse's Advocate website. You will then see all teeth according to their year of age as well as all teeth by view (straight on, left side, right side and open mouth.