Springtime in Alaska and a big bull moose is feeding on budding willows. Last fall this moose shed a rack that was five feet across and weighed about 50 pounds. Now he's sprouting the points that will become another massive set of antlers by the end of summer.
A bull moose grows a pair of antlers in just about six months, only to shed them every fall. They are the fastest-growing bone in the animal kingdom, and can grow almost an inch a day. The largest moose antlers on record were 83 inches across - almost seven feet wide - and the heaviest weighed 79 pounds. Growing a set of antlers is energetically comparable to a cow moose gestating a calf.
Nutrition is the most important factor influencing antler growth, but genetics and health also have an influence. If a moose is injured, with a broken leg for example, the antler growing on the opposite side of its body will be affected.
During the spring and summer when antlers are growing, they are covered with skin, called velvet, loaded with nerves and blood vessels that feed the rapidly growing bone. Velvet antlers are very sensitive and feel warm to the touch. A moose or elk can bolt through the trees and brush of a forest without snagging its antlers because they are well aware of just where they are - they develop this awareness when the antlers are in velvet and sensitive.
Antlers are not horns - horns are not shed. Deer, moose, elf and caribou have antlers; mountain goats and Dall sheep have horns.