Horses have evolved to survive by constantly grazing on whatever forages are available in their environment. This typically consisted of coarse grasses and other fibrous plant materials. The constant grinding motion of chewing and breaking down these materials to start the digestive process causes excessive wear and tear on the teeth, particularly the molars. In fact, if horses were born with teeth like ours, they would quickly wear them down to the gums with all that chewing, and ultimately starve. Instead, nature came up with an efficient system to continually replace the grinding surfaces on the teeth, ensuring that the horse could effectively break down plant material well into their twenties.

This is achieved by the evolution of teeth that continue to “grow,” or erupt, throughout the horse’s lifetime, until the root is effectively used up. Depending on how coarse the diet is, most horses have enough reserve crown to last at least into their twenties and often beyond.

Foals have a partial set of baby teeth, consisting of 12 molars (rear grinding teeth) and incisors (front nipping teeth) present at or shortly after birth. Behind those deciduous teeth are the roots of the full adult set, which start to come in around two years of age. Gradually, the adult teeth push the baby teeth, or “caps,” out and a full adult set of 24 molars and 12 incisors are present around five years of age. If you look at the skull x-ray in a horse under four years of age, it is easy to see the small rounded baby teeth sitting atop the long adult roots that are embedded deep in the jawbone. The adult molars in particular are so long that you can often see eruption bumps on the underside of the jaw and on the sides of the face because the underlying tooth roots barely fit inside the skull. On the other hand, if you were to observe the skull x-ray of a horse in its twenties, the molar roots are very short because most of the reserve crown has been used up through years of grinding.

Advertisement