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Photograph by Joe Mac Hudspeth, Jr. · www.southernfocus.com

Magazine


The Antler Growth Cycle

From the Fall 2003 issue

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The following is a scenario that plays out every fall and winter to countless hunters across Mississippi and across the country. The morning air is cold. The frost covering the ground is beginning to burn off thanks to the rising sun. The hunter is wishing that sun would hurry on up and reach his frozen feet. He catches himself daydreaming, with the sun now shining on his face, wondering what the morning will bring. Suddenly, footsteps in the leaves jolt him back into reality. There, through the woods, a doe is running. From behind her he hears the grunt of a buck. With adrenaline and instinct taking over, the hunter raises his weapon. A few minutes later the hunter is admiring the buck he’s been dreaming about. Or better yet, he’s admiring the antlers he’s been dreaming about. Many of you have been this person. Now that the animal is in hand, have you ever wondered what those antlers really are and how they grew? With all the rage to grow big antlers through deer management today, we need to gain a better understanding of the growth cycle of antlers to fully appreciate them.

Antlers hold somewhat of a magical mystique about them. They have been used for centuries in tribal rituals. They are used as medicines and even as aphrodisiacs in many cultures. They were first studied by Aristotle. Even today, they are proudly displayed by the hunters who pursue them in fall and winter. So what is an antler and why are they so special? Antlers are the fastest growing normal tissue known to man. Antler growth mimics the growth of cancer cells. Deer go through a situation very similar to osteoporosis when growing antlers in that their ribs become very porous and weak due to the lack of estrogen produced. Its no surprise then that most of the understanding we have of antlers and their growth process is due to medical research.

Dried antlers are composed of approximately 45% protein, 22% calcium, 11% phosphorus, and 1% fat. The remainder is comprised of trace amounts of other minerals and carbon. This is the reason that food plots should provide plants high in protein, calcium, and phosphorus (i.e. clovers, peas, soybeans, and other legumes) during the spring and summer growing seasons. The winter clovers planted in fall provide these necessary nutrients during the early spring, just after antler shedding and at the time new antlers are initiating growth. A diet of 16% protein is generally considered optimum for antler development, although as low as 10% may be adequate.

The antler growth cycle, called antlerogenesis, is controlled by both neural and endocrine (hormone) factors. The timing of antlerogenesis is controlled by a genetic clock relative to the photoperiod, or the amount of light in a day. The amount of light in a day must go from long to short to initiate the hormone production that begins antler growth. A study was conducted that kept deer in a room with controlled light. The light was controlled to “speed up” the normal year’s light cycle. The result was 3 complete antler cycles in one year by one deer. In contrast, when the light cycle was “slowed down” from the normal year’s, the antler cycle could be delayed up to 2 years. The timing of antler growth varies dramatically from north to south. In Mississippi for instance, antlers begin to grow much later than in northern states. In the tropics, where day length does not change, deer grow antlers at all times of the year.

Antlers begin to regrow almost immediately after the old antlers are shed. Once the old antlers are shed, a small, brief increase in testosterone is needed to initiate antler growth. After this brief increase in testosterone diminishes, the buck is now temporarily infertile. Once the antlers begin to grow, many hormones are needed to continue and complete the growth process. Much of this growth process is still not understood, but it is known that hormones such as the parathyroid hormone, estrogen, calcitonin, prolactin, melatonin,and growth hormones are involved.

As the antlers are growing, they are covered in a fuzzy skin called velvet. At this point the antlers are living tissue, and are very sensitive to the buck. The antlers themselves are full of blood vessels. As the antlers reach maturity, which is timed by the photoperiod, the blood vessels begin to close. When the blood vessels close, the testosterone level once again increases, causing the antlers to harden, or mineralize. Once mineralization is complete, the velvet skin begins to itch, prompting the buck to rub the antlers to remove the velvet. The shedding of velvet usually happens quickly, sometimes in just hours. When the velvet is shed, the antler is now dead bone, affixed to the skull via the pedicel. The buck, which has been infertile since shortly after shedding his old antlers, is now once again ready to breed.

As bucks get older, antler size generally increases up to maturity at 5-7 years of age. Average antler mass increases fourfold from yearling to 2.5 years of age and ninefold from yearling to 5.5 years of age. Antler points, main beam length, and antler spread generally increase with age. Approximately 80% of bucks will mature with 8 points. Some never attain 8 points and others may grow 30 or more. Antlers are classed as typical (points generally symmetric and arising from the top of the main beams) or nontypical (points arising from other than the top of the main beam). The frequency of nontypical points increases in older males. In southern herds, body mass and antler development of yearling males is related directly to date of birth. The later they are born, the smaller the body weight and antlers.

Now here are the results of some past studies on antlers you may find interesting. The hormonal changes a buck goes through annually results in the buck going through puberty each year. If you castrate a fawn buck before the pedicels are fully developed, the buck will never grow antlers. If you castrate an adult buck with velvet antlers, the antlers will continue to grow, but at a much slower rate, and the antlers will never harden. If you castrate an adult buck with hardened antlers, the buck will promptly shed his antlers, and the following spring will regrow antlers that will never harden. These last two scenarios result in a “cactus buck”. Finally, if you graft part of the pedicel to another part of the body, an antler will grow there. Who knows, maybe in years to come antlers will be growing not only on the head, but off the hips as well. Then that white flag would be waving between antlers to show us what we missed!