How Old is That Horse?

While age can be determined by teeth, horses at pasture will wear down their teeth faster than horses eating hay, grain and pellets

We've all heard the adage: "Don't look a gift horse in the mouth." Essentially that means: "Don't check his age."

Horsemen traditionally use teeth to estimate a horse's age, but it's not foolproof. A very young horse's age is determined by which teeth are present and which he's losing. After that, age is determined by the wear, making accurate age estimation relatively easy only until the age of 9 or 10.

Teeth are made of three materials that vary in hardness and wear away at different rates. The softest material wears down and makes shallow spots, while the hard enamel remains in more protruding ridges. In very old horses, Galvayne's groove, shape, slope and grinding surfaces are taken into account.

Baby Teeth
Baby teeth emerge soon after birth. Sometimes the two front teeth (top and bottom) are present at birth. These temporary milk teeth are smaller, whiter and smoother than permanent teeth, and have a slight indentation at the gum line.

The central incisors in front and first set of premolars in the back appear first. By the end of the second week of life, the next two sets of premolars appear. The second set of incisors usually comes at 4 to 6 weeks of age. The third set (the corners) appears between 6 and 9 months.

A yearling usually has all 12 temporary incisors (six on top, six on the bottom) and 12 permanent premolars. He also has four permanent molars farther back in the mouth, behind the premolars.

By the time he's 2, all his milk teeth are fully erupted and the incisors are all touching and showing wear - especially the centrals, which have been fully erupted the longest.

Temporary incisors are all present at age 2. Permanent incisors are all present and level by age 5. Between ages 2 and 5, some milk teeth are shed and some permanent teeth come in or grow up to the level of the others. But at both ages 2 and 5, the mouth is "level." The only visible difference is that a 2-year-old has baby teeth, while the 5-year-old has permanent teeth.

Baby teeth are shed in the order they come in, pushed out by the erupting permanent teeth. Sometimes a baby tooth doesn't come clear out, trapping the permanent tooth in the jawbone and causing an enlargement on the lower jaw. These "tooth bumps" are common in horses from ages 2 to 4. Once the offending baby tooth (called a cap) is removed or works loose, the trapped molar can erupt and the lump on the lower jaw disappears.

Permanent Teeth
The first permanent molars appear at the back of the mouth behind the baby teeth at 9 to 12 months of age. The second set replaces all the baby teeth by 2½. Baby teeth usually shed in the fall, starting with central incisors.

The permanent centrals are fully erupted by age 3. The next incisors push out the milk teeth at about 3½ years and are fully erupted by age 4.

The corner incisors erupt at age 4½ and are fully in wear by age 5, at which point the horse has a complete set of 24 permanent cheek teeth.

All baby teeth are replaced by age 4½ years. He'll have at least 36 teeth: 12 incisors and 24 cheek teeth. He may also have up to four wolf teeth and four canines.

Canines emerge behind the incisors at about 4 years of age, although not all horses get them. They occur most commonly in males.

Many horses develop another set of premolars, called wolf teeth, just in front of the cheek teeth, at about 5 to 6 months of age. They're often small, with short roots. In some horses, they don't appear until about 2 years of age. Some never erupt. Wolf teeth are often removed before a horse starts training because they can cause the horse discomfort from a bit.