Manuals for horse owners and veterinarians make it seem so easy. To find out the age of a horse, you simply open his mouth, study the intricate patterns of the upper and lower incisors for several minutes, and announce “This horse isn't 10 - it is clearly 14 years old.” Does it really work this way? Not really. Sometimes the best you can hope to do is to establish whether the horse is young, middle-aged or old.
Step One: Veterinary students taught by Dr. Bob Cook all knew the drill. Step one in determining a horse's age was simple - you ask the owner: “How old is this horse?” This wasn't really a joke. The owner, in some cases, is often the most accurate source of knowledge about a horse's age. Owners of home-breds will know to the day, and sometimes to the minute, how old a horse is. The owner who is fifth down the line for a grade horse, however, has information that is likely to be worn out.
Step Two: Ask if the horse has papers or a tattoo. Thoroughbreds and standard-breds who have raced will have tattoos that definitively establish their ages. In thoroughbreds, the letter A means a birth year of 1972 or 1999. The standard-bred lip tattoo employs a similar system, except that the letters N, M, O, and Q are not used to avoid misinterpretation.
If horses have papers, read them carefully to make sure that the description matches the horse. Observe the horse carefully. Look at the shape of his body, the way he walks,and the way he interacts with other horses and with people. General characteristics of young horses differ from those of older horses.
- The young horse: The young horse acts young. Out in the pasture, a chance wind under his tail makes him prance, leap and buck. He tends to be curious. Everything is still new to him. The young horse also has a youthful appearance. The back is straight with no hint of a sway; the area above the eyes is relatively flat; and if they are natural grays, the gray will still be quite dark. Other colors will not have any gray around the muzzle or eyes. The joints won't be creaky.
- The older horse: The older horse usually acts more settled and mature than the young horse. There aren't a lot of surprises left in life for this horse. He has an older appearance; the back has begun to sway; and there is a hollow over his eyes. The gray horse is nearly white, and the bay and chestnut may have accrued gray hairs, especially around the muzzle.
These are general hints and guidelines - there are many exceptions to the rule.
Step Three: Look in the mouth. Aging a horse by looking at his teeth is a very inexact science. Recent studies have shown that even experienced equine practitioners are not very successful at aging horses older than 8 by their teeth. This is primarily because each horse has variations in the rate at which his teeth grow and wear down. Some horses chew wood or rocks, or crib, further changing the appearance of their teeth. This being said, there are a few guidelines that are useful to know.
- Eruption times: This is one of the most accurate of aging procedures. Horses are born with very few visible teeth - and those that we can see are deciduous, or baby teeth, which will eventually make way for the permanent teeth. The incisors of the horse are as follows: a pair of centrals, then a pair of lateral incisors, and finally, a pair of corner incisors.
It is again important to determine if a horse is young, medium, or old. As most of us realize, horses have teeth that are continually growing - the corollary to this is that the teeth are also continually wearing down (otherwise, your horse would soon look like Bucky the Beaver). As the teeth wear down, the shape of the chewing surface, or table, of the teeth changes.
Foals: The rule of thumb is “7 days, 7 weeks, and 7 months.” This generally means the centrals appear anywhere from birth to 7 days, the laterals appear at 4 to 7 weeks, and the corners appear at 6 to 9 months.
Young adults: The rule of thumb is “2½, 3½ and 4½.” This means that most horses get their permanent centrals at 2.5 years, their laterals at 3.5 years, and their corners at 4.5 years.
After this, things get a lot more uncertain!
General appearance of the teeth: First, open the horse's lips and look at the jaw from the side. Young horses have teeth that have a vertical angle. As they age, this angle becomes less and less steep.
Table Surface of the Teeth: Next, open the horse's mouth and look at the table surface of the teeth. In general, you will find that the centrals are the oldest, and the corners the youngest teeth.
Note - try not to get bitten when you do this. The safest way to do things is to gently but firmly grasp the tongue at about the level of where the bit sits - this will help to keep the mouth open and prevent the horse's teeth from crunching your fingers.
The table surface of the teeth is rounder in younger horses and more triangular in older horses. Looking at the incisors in order, the central incisors are round between ages 6 and 12, and triangular between 8 and 18. The laterals are round between ages 6 and 13, and triangular between 9 and 19. The corners are round between the ages of 7 to 14, and triangular between the ages of 9 and 20. You can see that the intervals are already becoming quite widely ranged!
The second thing to look at is the cups of the teeth. This refers to an area that looks like a crater that is found in the teeth of relatively young horses. This cup fills with debris, and appears very dark. As the horse grinds the teeth down, the crater, and hence the cup, disappear. A rule of thumb is “6, 7, and 8.” In reality, the cups disappear from the centrals between the ages of 4 and 8, from the laterals between the ages of 7 and 10, and from the corners between the ages of 7 and 10.
Marks that traditionally were used for aging, such as Galvayne's Groove, and hooks, have been shown to be highly inaccurate, and we now discourage the use of these marks in aging.
The process of aging a horse is not simple and, in horses older than 6, it is likely to be quite inaccurate. Careful observation will help to determine if a horse is young, medium or old, but only knowledge of an actual birthday will let you be accurate to the level of saying that a horse is, for example, 16, or 22. Use all the information that you are given, and put it together to come up with a good guess as to a horse's age. Remember - even experienced equine clinicians can be fooled - quite easily.