If a horse’s date of birth is unknown, take a look at his teeth for clues on how old he is. Aging a horse this way isn’t 100% accurate, but it will give you an approximate age range. The younger a horse is, the more accurate the approximation will be. Here are four characteristics to look for to determine the age of a horse by its teeth.
Horses have two sets of teeth: temporary teeth called “baby” or “milk” teeth, and permanent teeth. In a 1-year-old horse, all the temporary teeth have erupted. By 3 years old, most horses will have permanent center teeth, both upper and lower. Permanent teeth are larger and darker than baby teeth. By the age of 5, all the baby teeth are replaced by permanent teeth and, at this point, the horse has a “full mouth.”
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On the grinding surface of the permanent incisors, there is an indented area with a darkish center in the center of each tooth. This is called the cup, and horses can be aged by their disappearance. At 6 years old, the cups disappear from the bottom central incisors. Then, at 7, they disappear from the intermediates and, by 8, they’ve disappeared from the corners. The top incisors lose their cups from the centrals, intermediates, and corners at 9, 10, and 11 years of age, respectively. By 12 years, the cups are gone, and a horse of this age is sometimes referred to as a “smooth mouthed horse.”
The Galvayne’s groove is a dark vertical groove that occurs on the outer surface of the upper corner incisor teeth in mature horses and extends down the length of the tooth. The groove first appears at the gum line in the center of the tooth when the horse is 10 years old. At 15 years old, the groove extends halfway down the tooth. By 20, the groove extends the entire length of the tooth. After 20, the groove begins to disappear from the top of the tooth; by 25, the groove will only be seen on the bottom half of the tooth, and by 30, the groove is entirely gone.
Angle of Incidence
As a horse ages, the angle of meeting between the upper and lower incisors becomes more and more acute as the incisors slant forward and outward. In young horses, the angle is between 160 and 180 degrees, and in a very aged horse, the angle might be 90 degrees.
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