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If you do not know a horse’s birthdate and there is no adequate paperwork, the animal’s appearance and its teeth are all you have to go on. You would be hard-pressed to age most people accurately from looking at them, and the same has to be true of horses.

Some wear better than others due to all sorts of variations in individuals, their environment, breeding and feeding.

If you do try to age a horse by its teeth, the incisors (the most obviously visible front teeth that sit in front of the bit) are the crucial ones to examine.

In younger horses, it is possible to make a good estimate from the number of baby and adult teeth that have erupted or emerged from the gum. This is quite easy to establish in a three-year-old, for instance, where there will be two adult incisors in wear in the centre of the jaw and baby teeth on either side.

However, it is not impossible to confuse a two-year-old with all baby incisors and a five-year-old with all adult incisors. In theory, the baby teeth are smaller and whiter, with a rounded gum line. But when you are looking at a single horse on its own, it can be tricky to decide how white and small the teeth actually are!

It is best to look for other clues such as the fact that the canine teeth or tushes, small extra teeth at the side, will have appeared in a five-year-old stallion, most geldings and some mares. In the past, it was not unknown for unscrupulous vendors to file down or remove the tushes to make an older horse look younger.

Once all the adult incisors have emerged and are in wear, age determination by the teeth becomes more difficult and accuracy of age estimation falls. You need to study several different features of the front teeth that change as horses age. These include:

  • The angle of the incisors as viewed from the side: an old horse is truly long in the tooth with long, slanting incisors, whereas a younger horse will have fairly short, vertical teeth. But this gradually changes and does not enable the age to be pinpointed. A five-year-old will have an almost vertical line between bottom and top front teeth, while in a horse of more than 15 there is almost a right angle between these teeth.
  • Theoretically a seven-year-old hook will appear on the back edge of the corner incisor, ie the one towards the outside, but research has shown that this is really inconsistent.
  • Another vague area is the Galvaynes’s groove, named after a Mr Galvayne, who wrote a book on ageing horses in Victorian times. He claimed he could accurately age horses up to the age of 30. The groove named after him, a brown streak again on the upper corner incisor tooth is said to first appear near the edge of the gum when a horse is about 10 years old, and gradually extends down the tooth to reach the bottom edge at around 20. It gives a rough guide that a horse is older, but is often different on the two sides of the mouth, so which side do you believe?

    The complicated bit of ageing by the teeth involves looking at various indicators on the top biting surface of the lower front teeth. These include:

  • The shape of the grinding surface changes with increasing age, being fairly oval in the young horse, more rounded by middle age and smaller and triangular in old age; however, unless you have a yard of different horses to compare, it can be hard to judge this objectively.
  • There are different patterns on the incisor grinding surface, which all the books on ageing consider. These are the cup, mark and dental star, which vary with the horse’s age. The cup is a dark coloured depression that appears in teeth that have just come through the gum. It is gradually worn away as the teeth wear down. Different books give different ages for this. The term “mark” refers to the area after the cup has worn away, while the dental star is a brown streak towards the front of the teeth, which becomes more circular and central in the older horse.

    The key point is that ageing by the teeth is not as simple, scientific or accurate as many suggest. The obvious answer is to follow the old advice to “never look a gift horse in the mouth”. Track down its correct documentation instead and then check it!

    This veterinary feature was first published in Horse & Hound (24 February, ’05)

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