The pronghorn is unique for two reasons. It is the only horned animal in the world that annually sheds the outer part of its horn. This outer layer is called the casque. The casque is pushed off each fall by a new horn growing underneath. The pronghorn is also the only horned animal in the world whose horn branches, creating the prong for which it is named.
Antlers are deciduous, meaning they are shed and grown new each year.
Among the females of the deer family, only the female caribou normally has antlers. The moose has the largest and heaviest antlers. This growth takes place in only a few months. Deer antlers also grow very quickly. A deer's main antler beams are known to grown as much as 15 mm per day.