Cover Story – Antlers are the fastest-growing structures in the animal kingdom…


July 01, 2016
Antlers are uniquely mammalian; they are the only appendages that annually replace themselves, and their phenomenal growth rate even surpasses that of dreaded cancer.

Antlers are actually two structures in one: the antler itself and the pedicle, or stump on the ends of which the antler develops. Antlers drop off and are replaced; pedicles are permanently attached to the buck’s head.

The annual cycle of antler growth, hardening, casting, and regrowth is controlled by the buck’s endocrine system. It involves a complex interplay between the hypothalamus of the brain, pineal gland, pituitary gland, and testes. The cycle is dependent upon seasonal changes in the amount of daylight, or photoperiod, and follows the rhythmic rise and fall in circulating blood levels of the male hormone testosterone.

Before antler regeneration can start, antlers must mature, die, and fall off. As soon as the old antlers drop, normally during winter, the swollen ring of skin around the pedicle grows over the stump of the antler — a process referred to as “wound healing.” This new skin is more like antler velvet, into which it will ultimately develop.

In Northern latitudes, whitetailed deer grow antlers in spring and summer, when testosterone production is at its lowest level. The pineal gland, tucked deep within the mid-portion of the deer’s brain, serves as the whitetail’s nerve and hormone transducer. That is, in response to changes in day length, the tiny gland translates light signals into chemical signals that cause hormone changes responsible for setting the whitetail’s seasonal rhythms. An increase in the amount of daylight during April stimulates greater production of a hormone known as prolactin that triggers new antler growth from the buck’s pedicles.

World renowned antler researcher Dr. Richard Goss demonstrated the importance of changing light regimes in regulating antler growth in Sika deer raised under controlled lighting. When light cycles were artificially shortened, the deer grew as many as three sets of antlers per year. When light cycles were lengthened, they only grew antlers every other year.

Because day length is nearly constant at equatorial latitudes, deer living in tropical and subtropical habitats experience only slight seasonal changes in the amount of daylight. Therefore, because of the lack of photoperiod cues, does may breed and give birth and bucks may carry hardened antlers, at any time of the year. But even in the tropics, bucks only grow one set of antlers each year, the timing of regrowth being determined largely by when the deer was born.

Before any deer can grow antlers, it must first grow pedicles. These structures first show as a pair of cowlicks on the forehead of very young fawns, where they can be felt as small bony lumps beneath the skin. Pedicles usually don’t become pronounced “nubbins” until the fawn is about four or five months old. This is when the young buck’s testes produce sufficient testosterone to stimulate the laying down of additional pedicle bone.

In the absence of testosterone or the presence of the female hormone estrogen, no pedicles form and antlers fail to develop later on. Buck fawns born late in the season, those poorly nourished during summer and autumn, or those subjected to severe social (psychological) stress due to “crowding” at high herd density tend to grow small pedicles (or possibly none at all), due either to a deficiency in testosterone production or because of a hormonal imbalance that blocks its effect.

In the Northern Hemisphere, the exact timing of antler growth varies somewhat among individuals, depending upon their age and general health status. Healthy, mature bucks may show signs of bulging new antler growth in early April. By comparison, new antler growth among malnourished mature individuals and yearling bucks growing their first set of full-fledged antlers may be delayed from two to four weeks. (Coat molt generally follows the same pattern, with mature, healthy individuals being the first to don their red summer coats.)

Early in their development, antlers are quite soft and easily damaged. Growth occurs at the tips, whereas calcification (hardening) starts in the shaft of the antler. (The core remains moist and spongy until the antler is cast.)

The growing antler contains an involved network of blood vessels and tissue which is covered by a hairy skin known as “velvet.” Although quite fragile and easily damaged, the live antler is richly supplied with sensory nerves. Even the delicate hairs serve as touch-sensitive feelers that warn of a pending collision. As an added safeguard, bucks seem to possess a special (kinesthetic) sense that permits them to judge their own antler size and shape. So equipped, even large-antlered bucks can bound through dense forest cover without damaging their soft antlers.

Antlers are the fastest-growing structures

in the animal kingdom. (Moose antlers, for example, may elongate at the astounding rate of three-quarters of an inch per day.) Although the live antler may remain velvet covered for about four to five months, most of the growth is accomplished during June and July. Completeelongation of the antler is normally completed within 100 days.