Why, how & when deer shed antlers

Dana R. Rogers Special to the Farm Forum
Farm Forum

Most outdoorsmen and women are crazy about antlers, whether they’re attached to a deer’s head or not.

While most people know that male deer shed and grow a new set of antlers every year, many don’t know the biology behind this amazing phenomenon.

The growth, mineralization (hardening) and casting (dropping) of a buck’s antlers are controlled by hormones and regulated by photoperiod, the amount of light per day.

A buck’s antlers grow during the spring and summer before they harden during late summer or early fall in response to a buck’s increasing testosterone levels. Typically, testosterone levels begin ramping up in July and peak in late October to early November during the rut, or breeding season.

After the rut, a buck’s testosterone levels drop through late December and remain at reduced levels through the following July. In other words, just as decreasing daylight and increasing testosterone levels cause antlers to grow, mineralize and shed velvet, increasing daylight and decreasing testosterone levels cause antlers to fall off each winter. Some deer shed their antlers as early as December, while some don’t shed until March.

Antler growth originates from a point on the deer’s skull called a pedicle. This secure connection can obviously withstand the impact from sparring, fighting and rubbing during the fall, and more than one hunter has dragged a buck back to the truck by the antlers, which begs the questions why and how they eventually fall off.

The antler and the living pedicle can only remain connected at times when a buck’s testosterone levels are elevated. When a buck’s testosterone levels fall significantly, a bone cell called an osteoclast removes the connective bone tissue by reabsorbing the calcium between the antler and pedicle, resulting in a buck shedding its antlers. Sometimes a buck will shed both antlers at roughly the same time, and other times a buck may shed one antler and carry the second for hours or even a couple days before shedding it.

Physical factors

More often than not, deer lose their antlers in late winter or early spring because of changing testosterone levels caused by photoperiodism. However, other factors can also have an impact on a buck’s testosterone levels and, as a result, when it sheds its antlers.

A buck’s physical condition can be a significant contributor to early antler shedding. For example, if a buck injures its testicles a reduction in testosterone levels will likely occur. Other bodily injuries, such as those sustained from fighting during the rut, a vehicle collision or a nonlethal hit from a bow or firearm, can also result in reduced testosterone levels and force early antler shedding. A buck could also cast its antlers early if it’s weary from the rigors of the rut or if it’s malnourished and experiencing nutritional stress or starvation.

Charles Alsheimer, who was an author and manager of a private, fenced-in deer herd, recorded dates when the bucks he studied cast their headgear. He noted that one of his captive deer regularly shed its antlers the first week in March for seven years. The only variance was during a year when the buck was injured fighting and cast its antlers much earlier on Christmas.

Studies performed by the Quality Deer Management Association in northern deer herds show that the most dominant bucks often shed their antlers earlier than younger, smaller bucks. The study suggests this may be related to nutritional status, as many older, more mature bucks are heavily involved in rutting activity and are subjected to more physical stress each fall. At the same time, the study also said that it may be related to the fact younger bucks experience less dramatic decreases in testosterone levels than older bucks.

One often overlooked factor of when bucks shed their antlers is the presence of does that have not yet been bred and are still cycling through estrous stages. According to George Bubenik of the University of Guelph in Ontario, Canada, an unbred doe’s pheromones can keep the testosterone levels of bucks in an area elevated well past the peak of the rut, which can lead to those bucks dropping their antlers later than normal.

Bubenik noted that in areas with poor buck-to-doe ratios that often see second- or third-cycle breeding or in areas with a good number of sexually mature doe fawns, bucks will often hold their antlers longer into the winter.

He also said another factor to consider is the influence fighting has on male deer. Herds with multiple bucks that continue to fight late into the winter can prolong elevated testosterone levels and cause unusually deep mineralization of the antler pedicle, which can delay antler shedding.

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Deer have antlers, not horns

• Antlers are not horns. Horns are two-part structures found on antelope, bison, sheep and other members of the bovine family. Whitetail and mule deer, elk and moose are part of the Cervidae family, which is often referred to simply as the deer family.

• On male deer, antlers are grown as an extension of the animal’s skull — they are bones that are shed and regrown each year.

• Antlers grow from a pedicle, which is the attachment point to the animal’s skull.

• When a buck’s testosterone levels drop after the rut or mating season, a new bone cell called an osteoclast removes the existing bone tissue between the pedicle and antlers, causing them to fall off.

— Quality Deer Management Association

Male members of the deer family grow and shed their antlers each year. Bucks can occasionally shed both of their antlers at the same time, but they more commonly carry one for a few hours or even days before it is shed, too. Photo courtesy of Lyle Glass, CaptureDakota.com