The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

6. Why Are Medical Researchers Interested in Antlers?

A L L T H I N G S D E E R 31 tion of orientation followed the magnetic north, which can be different from simple geographic north (in Minnesota, we’re a few degrees off). 6 why are medical researchers interested in antlers? During a recent autumn, I occasionally saw a year-and-a-half-old buck with Y-shaped antlers (a four pointer) on each side as he walked by my trail camera. The last time I saw him he had shed one side. I found the other side while I was taking a break from writing this very article. It had been dropped in the previous twelve hours. Wondering what is known about antlers, I did some digging in the antler literature and found that the medical profession admires them for entirely different reasons than hunters do. Limb regeneration is their interest. Yes, antlers are a lot like limbs. Among the vertebrates, creatures like salamanders retain the ability to regenerate tails and limbs throughout life. That is a useful trick if some predator grabs your tail—better to give it up and live on with a newly regenerated one. Humans actually have some limited capability to regenerate tips of fingers, but it depends on how the wound is treated after losing a terminal segment. But the power to regenerate is pretty limited in other vertebrates, especially mammals. With one big exception, antlers. The annual regrowth of antlers proves that mammals are not incapable of limb regeneration, but it doesn’t occur, except for antlers. In a 2010 scientific paper in the journal Gerontology, Uwe Kierdorf and Horst Kierdorf wrote, “Understanding the mechanisms controlling antler regeneration may thus assist regenerative medicine to achieve its ultimate, but t h e t h r e e - m i n u t e o u t d o o r s m a n 32 still distant, goal of inducing limb regeneration in humans.” It hadn’t occurred to me that limb regeneration and antlers had anything in common. Although antlers are grown and shed annually, they actually grow from permanent features on the skull called pedicles (from the Latin meaning “little foot”). After the pedicle is formed, first antler growth starts and is associated with decreasing testosterone levels. Those who have harvested young bucks will have noticed that the first antlers are usually simple, unbranched spikes that grow as extensions of the pedicles and lack the elaborate base (coronet or burr) that mature antlers have. Typically the pedicle gets wider (and shorter) at the base with age, and bucks grow progressively larger and larger antlers until about age six, when they start to ebb. Interestingly, the antlers begin to grow when the males are not in reproductive condition, and it is thought that increasing day length begins this process. We know that day length is a major factor because if you put deer in captivity and experimentally “speed up” the cycle of day length, red deer can grow two sets of antlers in a single year. Or if you reverse their seasons in captivity by changing their light-dark cycles by six months, you can get them to grow antlers six months out of phase. During antler growth, the skin over the pedicle area grows outwards and becomes “velvet,” which supplies blood to the developing bone. Antler growth can be very rapid—up to an inch a day in elk. Incidentally, antlers grow from the tips, not the base (like horns). This was figured out by putting one screw near the base and another near the tip of a growing antler and observing later that the one near the base was the same distance away from the base, but the screw at the tip was much farther away. Increased testosterone levels in summer stop antler growth and cause final development of the antler bone and shedding of the velvet (which the bucks help along by rubbing). Our buck is now armed and potentially dangerous or attractive, depending on whether the observer is another male or a doe (or you). A L L T H I N G S D E E R 33 The antler itself is formed from two different types of bone, a hard outer layer (or “shaft”) called cortical bone (hard, compact bone with few spaces and a porosity of 5 percent to 30 percent), and trabecular bone, sometimes called “spongy” bone owing to...