Horns or Antlers Fact Sheet

Many deer hunters and wildlife watchers eagerly search the woods and field edges each winter and early spring for sheds...the discarded racks from the heads of buck white-tailed deer. These sheds have been highly prized throughout the centuries for their beauty and sense of wildness they represent. People have crafted them into displays, jewelry, tools, and folk medicines. Hunters often mistakenly call these shed racks horns. These boney projections, however, are not horns, but antlers.

Antlers are temporary projections of bone grown and shed each year. Though the bone looks quite solid, it has a honeycombed structure at the microscopic level. Antlers arise from a pair of pedicels. These are knobby, skin-covered nubs protruding from atop the buck's skull, between the ears. Pedicels are permanent structures and are the point at which the antlers break off and regenerate. Antlers are found only on cervids, such as deer, elk, moose and caribou. They are generally found only on males, although in caribou both males and females have antlers. But even in white-tailed deer some does have been known to sprout antlers, due to a hormone imbalance. With the exception of young males, most adult antlers display a branching pattern. Deer antlers can weigh, on average, between 3 to 9 pounds. By the time the antlers are in top condition in the fall, the bone tissue has stopped growing and is dead.

True horns are found on bovids such as mountain goats, bighorn sheep, bison and pronghorn antelope. Horns are permanent, continually growing projections of living bone protruding from the skull. They are sheathed in a layer of keratin, a tough, dense substance like that found in horse hooves. Except for the pronghorn antelope, horns are usually unbranched and remain on the animal throughout its life. Pronghorns, as the name indicates, are two pronged and they shed the outer sheath of keratin every year. Horns are usually found on both males and females.

The fascinating and complex annual cycle of antler growth is controlled by the relative length of daylight versus darkness as it changes with the seasons. In a deer, the brain's pineal gland reacts to the changing length of daylight by signaling the pituitary gland to activate changes in certain blood hormones. Testosterone, is a male hormone that circulates in the blood. As the daylight increases in mid-March and April, the production of testosterone increases in bucks. This hormone triggers a change in a number of male reproductive features. For instance, the antlers begin growing from the pedicel. Neck muscles also increase in bulk to aid the buck in keeping its head erect with the added weight of the antlers. Usually antlers begin to grow in a backward direction, then quickly sweep forward.

During the early spring and summer, deer graze and browse heavily to replenish the fat reserves they depleted during winter. Does must obtain energy to make the milk that they use to nurse their newborn fawns. Bucks use some of this new energy to grow antlers a process that requires a substantial amount of protein and minerals. Although spring nutrition is important for body and antler growth, deer possess adaptations that allow them to prosper in areas with mineral deficiencies. For example, deer deposit minerals in their skeletons throughout the year. Then, during antler growth, they mobilize these minerals to help the antlers grow strong. A second adaptation is the deer's ability to change absorption rates of minerals in their stomach. When using large amounts of minerals for antler growth, deer siphon more minerals from their diet. Deer rely on plants for these minerals, and they select plants offering the highest mineral concentrations.

Antlers in the early stage of growth are covered with a fuzzy skin that contains a tremendous concentration of nerves and a vigorous supply of blood. This fuzz is called velvet. The velvet nourishes the growing antler for about five months. Antlers are the fastest growing tissue in any mammal. They grow at an astonishing rate, between a half inch to one inch or more a day. Velvet is unusual in that it is a naturally occuring regenerative skin.

During development, antlers are very delicate and extremely sensitive to the touch. Deer in velvet try to avoid any contact with their antlers. The delicate nature of these velvet antlers make them quite prone to damage or breakage. If an antler is injured during this period of rapid growth, it may become mishapen for the remainder of the year. Some of the unusual antler racks reported each year are due to genetics, but many are the result of an injury to the growing antler itself or even to another bone in the deer's body. For instance, if a buck injures its leg, the antler on the opposite side of its body is affected. An abnormal left antler may indicate previous damage to a limb on the right side of the body, while an abnormal right antler may indicate damage to a left limb.

By August or early September antlers are fully-grown. They have stopped growing and the bone begins to die. The velvet "skin" dries up and falls off. Some people mistakenly believe that bucks rub their antlers on saplings and small trees to remove this dried velvet because it "itches." However, some bucks spend days with dried velvet draped across their antlers, heads and eyes. Also, the dried velvet contains no living nerve tissue so it cannot "itch." The best explanation for bucks rubbing their antlers on trees is that they are sparring with the limbs and trunks to strengthen their neck muscles in preparation for future duels with other bucks during the upcoming rut. Rubbing also releases aggression or anxiety brought on by the changes in hormones. Rubbing helps communicate to others in the area. A buck typically rubs a tree sapling with its face as well as its antlers. This action spreads scent from the lacrimal gland (similar to our tear ducts) to the tree limb. Bucks spread this scent around by rubbing the limb with their antlers. The scent advertises the buck's presence to other males and females.

As rubbing continues into the rut (from late October through November), the antlers acquire a polished look and the bucks become very aggressive toward each other. This is the time of year when the distinctive sounds of sparring bucks may be heard in the woods. These rigorous shoving matches function as a mechanism to decide which buck gains access to territory and females for breeding. Many confrontations consist of simple "display" matches where bucks position themselves and their antlers in order to impress their rivals and get them to back down without physical contact.

Sometimes, however, bucks actually battle fiercely and may receive serious wounds. Sometimes they may kill their opponent. Sometimes the tines of the antlers lock together during combat. Because the bucks do not have as much strength in their backward yanks as they have in their forward thrusts, they sometimes cannot unlock themselves and so subsequently die a slow and merciless death. Sometimes, the stronger buck will drag the weaker buck around for days, but it, too, will eventually die. These duels help assure the natural selection of the strongest, dominant bucks who will be able to pass along superior genes to subsequent generations.

In addition to sparring with their opponents, bucks also use their antlers to dig in early snows in search of food.

After the rut, length of day continues to decrease and so does the testosterone level in the blood stream. The connection between the antlers and the skull's pedicels weakens and the bucks eventually shed their heavy racks. This process takes only two to three weeks to complete. Depending on the severity of the winter, white-tailed deer bucks may drop their antlers beginning in late December, but more typically they shed their antlers in January or February, and sometimes even in early to mid-March. Deer on poor quality habitat lose their antlers sooner than deer on good quality habitat.

Antler growth is closely linked to nutrition. When a young buck reaches 10 months of age, its first set of antlers begins to grow. Yearling bucks usually carry spikes. These are antlers with a single bone having no branching pattern. These first year antlers are small because the young buck’s body is still growing rapidly and its nutrition is directed more toward muscle and skeletal growth than to antler growth. Older bucks may also carry spikes if they come from an area with poor food conditions. Bucks in high quality habitats tend to grow much larger antlers. While genetics has an influence on antler growth and size, nutrition by far has the greatest impact.

Some animals with horns can be aged by examining microscopic rings at the base of the horn. However, since antlers are temporary and shed each year, there is no record of the previous year's growth. Thus there is no good relationship between age and the number of antler points.

Searching for "sheds" is a fun activity to do in late December, January and February. So get out there and enjoy the cold fresh air!

Author:
Mary Kay Salwey, Ph.D.
State Wildlife Education Specialist
Wisconsin Department of Natural Resources

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