They grow for about 150 days a year. They can grow nearly 1 inch per day, making them the fastest normal growing tissue known to man. Humans have cherished them for thousands of years, and that’s especially true for deer hunters. Of course, I’m talking about deer antlers.
Native Americans used them for tools, buttons and beads, and modern Americans have similar uses for them. Cherokee legend even describes a race between a deer and rabbit, with the victor winning the right to wear antlers. Then and now, we remain fascinated by these amazing appendages.
I get a lot of questions about antlers. I am routinely asked what causes the “burrowed holes” you occasionally see in antlers. I have heard many hunters speculate they are caused by some species of fly that bores into the antler while it is in velvet. This sounds logical, but is it true? There is also a lot of interest in antler development by the medical world. Unless they were hunters, why would doctors be interested in antlers? Let’s look at some facts about antlers and then discuss these questions.
The Antler Growth Cycle
Antlers are secondary sexual characteristics – like beards in humans. The antler growth cycle is called antlerogenesis and is driven by photoperiod and hormonal factors. That’s why bucks shed their velvet at nearly the same time every year. In fact, in photoperiod-controlled experiments, deer can grow multiple sets of antlers per year or retain their antlers for more than one year.
Bucks begin to grow new antlers almost immediately after shedding the old ones, and antlers grow from pedicles located on the frontal bone. If you remove the pedicle, the buck can’t grow an antler, and if you damage the pedicle, the antler will have abnormal growth.
A brief increase in testosterone is necessary to initiate antler growth in spring. Once growth begins, testosterone levels diminish, and bucks become temporarily infertile. Their normal hormonal cycle results in bucks going through puberty each year.
If testosterone is administered to a buck while in velvet, his antlers will harden. If testosterone is administered to a buck while in hard antler, his antlers will be retained, and sustained high concentrations of testosterone will prevent the growth of new antlers.
Researchers have studied this process by blocking testosterone production in bucks at different stages of antler growth. If a buck fawn’s testosterone production is interrupted before his pedicles are fully developed, he will never grow antlers. An adult buck in velvet will continue to grow at a much slower rate, but the antlers will never harden. An adult buck with hard antlers will quickly shed them, and he’ll grow new antlers the following spring that will never harden.
The above results can also be observed in wild bucks that injure one or both of their testicles, interfering with testosterone production. This is generally what causes the “cactus” bucks or “perukes” that a few hunters shoot each year.
A small percentage of does grow antlers, too. This is generally caused by increased testosterone levels. These does have enough testosterone to grow antlers but generally not enough to harden them, so they remain in velvet.
Mineral Requirements to Grow Antlers
The mineral requirements for antler growth exceed those for skeletal growth and maintenance. In some species it is three times higher. Bucks satisfy this mineral demand from their diet and their bones.
During peak antler growth, the thyroid gland releases a calcitonin to allow bucks to resorb or “steal” minerals from their bones. This process causes bucks to temporarily go through osteoporosis. Their ribs and shoulder blades contribute the most to the temporary mineral deficiency, and they may lose up to 40% of their calcium content while the antlers are hardening. This loss of minerals causes their ribs and shoulders to become porous and weak, but by September deer can fully replace the minerals borrowed from their skeleton.
Interestingly, young bucks have dense antlers that become more porous as they age. Antlers contain more collagen than long bones such as femurs – this permits more flexibility and allows the antler to yield more before breaking. This feature is very important as bucks mature and engage in serious rut-related combat.
Antlers in Strange Places
Moving material from an antler pedicle to another region of the body results in growth of antler tissue in the new area. Scientists have transplanted antlerogenic material from a pedicle onto the forehead of mice and caused them to grow antler-like projections. They have also transplanted this material onto the lower leg bone of deer and caused them to grow an antler from their leg.
I have observed bucks with a third antler arising from their forehead or face region that clearly originated separately from their other antlers. Often this results from injuries to the skull near the pedicle.
One such buck was taken by a bowhunter. Upon closer inspection of the cleaned skull, I noticed a broadhead lodged in the left eye socket. This buck had been hit by an archer during the previous season, and he broke the arrow off and survived the injury. The arrow had sliced the pedicle and lodged in the eye socket. During this process, the broadhead moved some antlerogenic material from the pedicle to the eye region. The following season the buck grew two normal antlers plus a third short spike from just above his left eye.
Antlers in Medical Research
Since antlers are the fastest-growing normal tissue, and their shedding from the pedicle is the fastest deterioration of living tissue, medical scientists are interested because they hope to learn how cancer cells grow so quickly by studying antlers. This will aid our understanding of bone pathologies, because rapidly growing antlers mimic certain bone cancers. In addition to medical scientists, antler growth has attracted the attention of pathologists, endocrinologists, bioengineers, ethologists, evolutionary biologists, and of course, hunters.
The late Dr. George Bubenik, former professor of Zoology at Guelph University in Ontario, was a noted expert in antler growth. Some of his research focused on how scientists could use embryonic stem cells that induced antler growth to treat human ailments. Embryonic stem cells allow for the regrowth of antlers each year by differentiating into skin, blood vessels, cartilage and bone. “Deer antlers are strikingly similar to human limbs, consisting of bone, cartilage, skin, blood vessels and nerves,” said Dr. Bubenik.
If scientists could duplicate the antler growth process in humans, we could potentially regrow severed fingers and limbs. Additionally, if we also understood the process of temporary osteoporosis in deer, we could likely treat arthritis, immune disorders and degenerative diseases such as osteoporosis in humans.
Holes in Antlers?
Finally, what about those supposedly “burrowed” holes in antlers? Is there a species of fly that lives on antlers? Yes, and it is appropriately named the antler fly (Protopiophila litigata). It is a small fly less than 1/8-inch long that breeds exclusively on the antlers of cervids such as deer and moose. Antler flies mate on antlers from late May through late August and the female deposits her eggs into the minute cracks or pores in the antler surface. However, this only occurs on shed antlers and not on velvet antlers! The antler fly is found in eastern Canada, but even where it lives, it does not burrow into antlers. So, the antler fly is not responsible for the holes we see in some antlers.
These “holes” are often called foramens, but technically foramens are openings in bones where nerves, blood vessels or muscles pass through. In the case with antlers, it is simply an opening or hole. So, what actually causes them?
I asked numerous deer researchers if they were aware of any studies identifying the cause of holes in antlers, and none were aware of a single study. I have observed deer at captive research facilities with blood on the surface of an injured velvet antler. This blood often attracted flies and may be the cause of speculation about the role of flies in this scenario.
In the few cases I observed, the bucks injured their antlers on a fence and the flies arrived afterward. Free-ranging bucks can injure their growing antlers in many ways, and holes may simply be the result of such injuries. It is unlikely they are caused by a boring fly or other insect. I think the most likely explanation is these holes result from a small injury to the growing antler.
Antlers have fascinated us for centuries. Hopefully the information in this article will instill additional fascination for antlers and respect for the wonderful creature that grows them.