Just like humans, all horses replace the milk teeth with permanent teeth. Every horse change 24 teeth between the age of 2.5 and 5 (this period can vary from breed to breed).
Young horses usually have something called “eruption cysts”. These are bumps (bone enlargements) that we can see and feel on the lower jaw, and more rarely on the upper jaw. Eruption cysts are caused by vascular and bone changes during the formation and eruption of permanent teeth.
Usually, they don’t affect the horse, but it is good to check young horses regularly to make sure that the process goes smoothly.
Problems may arise if the permanent tooth is pushing with a wrong angle or in case of a retained milk tooth. If this happens, the cyst can become inflamed. Then, it will be hot and painful at touch.
In the photos below there are a couple of examples that I have come across recently.
Sometimes, bad cases must be referred to vet practitioners for x-rays and evaluations of teeth and skull.