Antlers are bony structures grown primarily by deer that are shed and regrown annually. They differ fundamentally from horns, which are permanent features composed of a bony core covered by a keratin sheath, as seen in animals like cattle or goats. Whether deer antlers possess nerves depends entirely on the stage of the annual growth cycle. This means the deer’s headgear transitions from being one of the most sensitive parts of its body to being completely insensate bone.
The Living Tissue: Nerves in the Velvet Stage
The initial growth phase is characterized by a soft, fuzzy covering known as velvet, a specialized skin layer. This velvet is packed with a dense network of blood vessels and sensory nerves. The presence of these nerves makes the growing antler an acutely sensitive part of the deer’s anatomy.
The nervous supply regenerates annually, arising from the trigeminal nerve via the supraorbital and temporal branches. This extensive neural network helps the deer monitor the rapid growth, which can proceed up to one inch per day in some species, making it the fastest-growing tissue in any mammal. The sensitivity of the velvet causes the deer to be careful, avoiding rough contact that could injure the delicate, actively growing bone tissue beneath.
Loss of Sensation: Antlers After Mineralization
Rapid growth concludes when the soft, spongy antler structure begins mineralization. This structural change involves replacing cartilage with solid bone, which rapidly hardens the antler. As the antler mineralizes, the abundant blood flow present in the velvet stage is systematically cut off, a process triggered by hormonal changes.
The loss of blood supply leads to the death of the overlying velvet tissue, which then dries out and begins to peel away. The deer actively rubs its antlers against trees and shrubs to accelerate the removal of this dead, irritating layer. The resulting hard antler is composed of dense, dead bone tissue that lacks any living cells, blood vessels, or nervous connections.
Once the velvet is shed, the antler becomes completely insensate. This loss of feeling is biologically necessary because the hardened antlers are used extensively for sparring and fighting during the rut, or breeding season. Without sensation, the deer can engage in head-to-head combat and absorb impacts without experiencing pain in the structures themselves.
The Annual Cycle of Antler Growth and Loss
The entire cycle of antler growth, hardening, and shedding is regulated by fluctuations in the deer’s hormones. These hormones are synchronized by the changing length of daylight, known as photoperiod. Increasing daylight in the spring initiates a decrease in melatonin, which signals the start of new antler growth. Antler development proceeds through the summer when testosterone levels are relatively low.
As summer progresses toward fall, rising testosterone levels trigger the end of the growth phase and the onset of mineralization. High testosterone levels are responsible for the cessation of blood flow and the subsequent shedding of the velvet. The hard, polished antlers are maintained throughout the autumn rutting season, allowing males to compete for dominance and mating rights.
Following the breeding season, typically in late winter, testosterone levels drop significantly. This decline signals the formation of an abscission layer, a specialized layer of cells between the antler and the skull. Specialized bone cells called osteoclasts remove calcium from this junction, weakening the connection until the entire antler breaks away and is shed, completing the annual cycle.