The Practice of Aging a Horse By Their Teeth
Between picking up a new horse or wanting to confirm the age of one that has been in your herd for years, the practice of aging a horse by their teeth is a useful tool to determine approximate age. However, every horse is different and therefore it is important to remember that it is not always going to be exact, but can usually give you a pretty accurate guess.
There are 4 main ways to estimate the age of a horse based on teeth appearance:
Presence of deciduous vs permanent teeth
The dissapearance of tooth cups and appearance of dental stars
Tooth shape and wear
Tooth angle
Presence of Deciduous vs Permanent Teeth
Foals begin to acquire teeth during the first weeks of life. The incisor or “front” teeth on a foal, specifically the very front four, erupt first. An easy way to remember eruption times of deciduous (baby) teeth is typically that the first set of front/central incisors (two above and two below) appear around 8 days, the second set beside them around 8 weeks and the third corner incisors appear around 8 months. The premolars begin errupting around two weeks of age, and by nine months old a foal has a complete set of 24 deciduous teeth. Baby teeth can be recognized by a lighter colour, smaller size and wider shape than permanent teeth.
At around 2 and a 1/2 years old, permanent teeth of the central incisors are again the first ones to appear. They are followed by the intermediate incisors beside them around 3 1/2 years of age and the corner incisors at 4 1/2 years. It has also been getting permanet molars pushing through during this time. By the time a horse is 5 years old, it has a complete set of 42-46 adult teeth. A “cap” is present when a baby tooth is still sitting on top of a permanent tooth once it has already erupted through the gum, and can sometimes need to be manually removed by your veterinarian during a routine float. In regards to both incisors and premolars/molars, the deciduous teeth should only ever be removed if it is mobile or the permanent tooth is fully erupted below it. Removing a baby tooth prior to the eruption of an adult tooth in order to “make room” is not an acceptable practice.
Pictured is a full set of deciduous incisors. They are creamy white in color, small in size and wider then they are tall. Going by what we learned today, this horse is older than 8 months (because all 3 sets of incisors are errupted) but younger than 2 1/2 years (because no permanent teeth are present yet).
This foal has his front and lateral baby teeth, however the last corner incisor sets have yet to erupt. This means that the foal is older than 8 weeks but younger than 8 months. For both of these two provided examples, we would utilize other aging practices to estimate the age even more accurately.
The Disappearance of Cups
At 5 years old all adult teeth will be present and cups are prominent on all incisors. The “cup” is the center of the top of the tooth that has a brown oval infolding, or cupped appearance. Wear of the top surface of the tooth causes cups to get smaller as they wear down until they are worn away completely, typically in a certain order due to the order of appearance of the teeth themselves. We know that the central incisors appear first, followed by the intermediate and then the corners. The teeth that appear first conjunctively wear down and lose thier cups in the same order, as the first to appear means they have the longest amount of wear. The lower incisors wear first due to having more shallow cups than the upper incisors naturally. The cups tend to dissapear on the central lower incisors at 6 years, the intermediate lowers at 7 years, the corner lowers at 8 years, followed by the center upper incisors at 9 years, the intermediate uppers at 10 years and by 11-12 years old, cups should have worn away completely. As cups wear away, “dental stars’ become more prominent on the tooth. Dental stars are actually the central pulp cavity of the tooth. They appear first as thin lines in front of the cup, then eventually as dark circles in the center of the tooth where the cup used to be.
Based on the information shared so far, we know that if a horse has all of their adult incisors present they are atleast 4 1/2 years old, and we can then further examine thier cups to determine a more exact age. The use of cup appearance is most useful if you know the horse is less than 10 years old.
Below is an excellent graphic from Redwings Horse Sanctuary as well as a photo of the lower incisors of a young horse (all cups are still present).
Tooth Shape and Wear
Tooth shape of the incisors is another helpful tool to examine in conjunction with other indicators. We know that when cups are present in young horses the tooth shape, when looking at the top of the tooth, tends to be more wide and flat. From 12-17 years old, the tooth continues to to be worn to a more round shape with natural wear and by 18-20 years old (when a horse is typically considered a senior), the tooth appears as a triangular shape. We know that deciduous or baby teeth, when viewed from the side, are wider than they are tall. As the tooth grows out, it will at one point be a perfect square (around 10 years old) and then will continue to grow taller than it is wide. A darkened groove, known as the galvaynes groove, can be another indicator of age on horses over ten years old. The galvaynes groove appears on the upper corner incisor at 10-11 years old, is said to be halfway down the tooth at 15 years old, all the way through the tooth at 20, halway back up the tooth at 25, and dissapears completely by 30 years old.
This corner incisor is not quite square anymore and the galvaynes groove is not quite halfway down the tooth. This horse would be expected between 11-13 years old.
Tooth Angle
The angle formed by the meeting of the upper and lower incisor teeth (in profile view), referred to as the angle of incidence, slants forward and outward as the horse ages. The contact changes from approximately 160-180 degrees in young horses to almost 90 degrees in an old horse. The “hook” that can sometimes develop on the corner incisors, usually appearing around 7 years of age and is something that is taken care of by your veterinarian during float appointments, is due to the incomplete meeting and lack of wear from the changing angle of incidence.
Photo/graphics credit: David Ramsey, DVM
Putting it all together, we monitor permanent tooth eruption to know the age of horses under 4 1/2 years. We know a horse is over 4 1/2 to 5 years old when they have all thier incisors erupted. If the corner incisor is still wider then it is tall, we know they are under 10 and can then use cups to get the age of between 5 and 10 years. If the corner incisor is taller than it is wide, we can examine incisor shape, the galvaynes groove, the angle of incidence and the appearance of the dental stars to determine the age over ten years.