Deer antlers are one of the most remarkable examples of tissue regeneration in the animal kingdom. Unlike horns, which are permanent and made of keratin, antlers are temporary bony structures that are shed and regrown annually from permanent bases on the skull called pedicles. This entire process is closely tied to the deer’s hormonal cycle, which is controlled by the changing length of the day, known as the photoperiod. This annual cycle ensures the male deer, or buck, has fully developed, hardened antlers precisely when they are needed for the autumn breeding season.
Initiation and Early Growth
The annual growth cycle begins shortly after the previous year’s antlers are shed, typically between late December and early March. New growth starts in the spring, generally in late March or early April, as two small bumps emerge from the pedicles. This phase is triggered by increasing daylight hours, which causes a decrease in the hormone melatonin. The drop in melatonin, combined with rising growth hormones, signals the body to start regeneration.
During this initial stage, the developing bone is covered in a soft, fuzzy skin called velvet, which is densely packed with blood vessels and nerves. The velvet acts as the transport system, delivering the nutrients and oxygen required to fuel the rapid growth. The growth rate is fast but not yet at its maximum, as the buck is recovering from the nutritional stress of winter. Antler growth is costly, often requiring the mobilization of stored mineral reserves, such as calcium and phosphorus, from the buck’s skeleton.
The Period of Maximum Growth
The period when deer antlers grow the most rapidly is during the late spring and early summer, typically spanning June and July. This phase is characterized by an explosion of growth, where mature bucks can add as much as a half-inch to one inch of new bone per day. This speed makes the antler one of the fastest-growing tissues known in mammals.
This peak growth rate is supported by two main factors: the environment and hormonal regulation. The longest days of the year in June and July provide the optimal photoperiod to sustain the high levels of growth hormones. Concurrently, this time of year offers the most abundant and highest-quality forage, rich in the proteins and minerals needed to build the bony structure. This combination of maximized nutritional intake and synchronized hormonal activity allows the deer to establish the full frame and length of the antler, with tines developing rapidly in July.
Antler Hardening and Velvet Shedding
As summer passes and daylight hours begin to shorten in late July and August, the growth phase slows down and eventually ceases. This change in photoperiod signals an increase in testosterone levels, which triggers the final stages of the cycle. The rising testosterone causes the blood flow to the velvet to be restricted and cut off at the base of the antler.
With the blood supply gone, the soft velvet tissue dies and begins to dry out. This desiccation coincides with the mineralization of the antler, where the soft structure turns into fully hardened bone over 20 to 25 days. The buck then actively rubs its antlers on trees and brush, peeling away the dead velvet, which can take a few hours to a couple of days. The resulting hardened antlers are prepared for the breeding season, used for establishing dominance and fighting rival males.