The Whitetail’s Annual Miracle: Antler Casting and Regeneration

antlergrowthEditor’s note: Spring is a time of rebirth, and nothing illustrates that like the whitetail’s annual cycle of antler loss and regrowth. Here are some incredible insights into this process courtesy of Deer & Deer Hunting‘s John J. Ozoga.

Antler Casting

Although the timing of antler growth is quite synchronized by photoperiod, generally starting during April and May in the Northern Hemisphere, the timing of antler casting tends to be quite variable. Some bucks might drop their antlers as early as late November, but others might carry them until late April, depending on their age and health status.

Antlers are cast when blood levels of testosterone decline. The maintenance of connection between the dead tissue of the antler and the living tissue of the pedicle is possible only during the period of high testosterone.

As soon as the testosterone concentration drops to a certain level, the narrow bridge of bony tissue between the pedicle and antler erodes away, and the antler falls off. This process by which the dead antler is separated from the living pedicle is unique, resembling a form of self-amputation.

Any factor that helps maintain elevated levels of testosterone will prolong antler retention. A buck’s nutrition and health status are factors of primary importance in determining the time of casting. If the buck does not remain in good physical condition, his testosterone level will decline to the point of triggering antler casting.

According to Canadian researcher George Bubenik, “There is some evidence that sex pheromones may activate and prolong the testosterone secretion in males … and delay the timing of antler cast.”

Hence, excellent winter nutrition could account for mature bucks maintaining good physical condition, high testosterone levels and prolonged antler retention, as typically occurs in the Midwest farmland. But the presence of estrous doe fawns during winter might also contribute to prolonged antler retention via sex hormone stimulation.

 Antler Growth

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 the Northern Hemisphere, the exact timing of antler growth varies somewhat among individuals, depending on their age and general health status. Healthy mature bucks might 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 might 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 coat.)

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 that’s covered by a hairy skin known as velvet. Antler velvet is capable of enormous expansion, necessary to keep pace with the antler’s rapid growth rate.

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.

Also, arteries supplying blood to growing antlers have unusually thick walls. When severed, the thick muscular walls quickly constrict, reducing blood loss.

Although the live antler might remain velvet covered for four to five months, most of the growth is accomplished during June and July. Regardless of deer body or antler size, complete elongation of the antler is normally completed within 100 days. This means large antlers grow at a much faster rate than small antlers. (For example, moose antlers might elongate at the rate of 3/4 inch per day.)

The completion of antler growth, antler mineralization and velvet shedding are closely linked to autumn’s shortening days. These changes are brought on by sharply increasing testosterone production.

The antler’s outer surface hardens quickly in a few weeks before velvet is shed. However, mineral deposition in the antler core is more prolonged. Bone formation starts internally in lower portions of the antler and progresses from the base to the tips as antlers elongate.

By midsummer, the pedicle becomes semi-mineralized, restricting blood flow to the antler core. As a result, during late stages of growth, the antler is nourished primarily by arteries in the velvet.

As the blood flow shuts off in the velvet vessels, the bone gradually dies, dries and sheds the velvet, thus killing the antler. Velvet death normally takes several weeks but can occur suddenly. Generally, death and stripping of the antler velvet signal death of the antler core itself.

Deer & Deer Hunting Magazine

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