Unlike other species of deer, both male and female reindeer, or caribou, grow antlers. Both sexes grow and shed antlers annually. As they develop, the bones are covered in "velvet," which supplies blood. LiveScience indicates that antlers grow as much as an inch a day. When fully grown, the antlers lose their velvet. In early winter, the antlers of the males drop off, while females don't lose theirs until later winter, according to the National Zoo.