Why do deer shed their antlers?

Deer shed their antlers annually as a prelude to the regeneration, or re-growth, of new ones.

The entire shedding process takes a mere two to three weeks to complete, and the re-growth phase takes place over the summer. The docile male deer that, with the exception of the male and the female reindeer, solely sports antlers sheds them between January and April, after the autumn mating season draws to a close. He can do without antlers at this time, because his need for them in prior months, to attract and to impress females for his harem of mates, and to fight with his competitors for the females' affections, no longer exists.

The antlers themselves differ from the hollow horns of cattle, in that they comprise solid bone tissue with a honeycombed structure. Pedicles, or knobby, skin-covered nubs protruding from the skull, support the deer's antlers, or points, which range in number from one shaft to eleven branches. The pedicles are a permanent fixture on the deer's forehead, and are the point from which the antlers annually break off.

During the first year the pedicles appear on the young deer's forehead. The following year, the youngster sprouts straight, spike-like shafts, and in the third year, the first branch appears. In successive years, as the deer matures, his antlers lengthen. In most species, he acquires additional branches. One can actually determine the age of the deer from the number of branches on his antlers, as their number increases with age.

During the growth phase of the bony antlers, they are covered with a sensitive skin referred to as "velvet," which is filled with blood vessels that feed the antlers the vitamins and the minerals necessary to build up the bone, and to promote normal antler growth. Antler growth spans two to four months, after which time the velvet is no longer needed, and a ring, which effectively serves as a shutoff valve, forms at the base of the antlers and cuts off the blood supply to the velvet. As a result, the velvet withers, dries up, and falls off, often assisted by the deer, which rubs his antlers against tree bark. The antler regeneration is complete, and the shedding cycle will resume once mating season in the fall concludes.