Antlers, a unique anatomical feature of the deer family, are one of the most impressive examples of bone growth in the animal kingdom. Unlike horns, tusks and other growths, antlers fall out and regrow each year in a dramatic and rapid cycle.
While this cycle is guided by general biological processes, there are a number of factors that affect how fast and how big the antlers grow. Since antlers are especially visible features, understanding these factors helps you better manage your herd and maintain their health and well-being.
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Why Do Deer Grow Antlers?
The first thing you should know about if you want to get the most out of your deer’s antlers is why they grow them in the first place. Antlers are a unique feature to the deer family, or cervids, which includes whitetail deer, elk and moose. All species in the family except for one, the water deer, grow antlers, and in all these species, with the unique exception of reindeer, only the males grow antlers. Scientists believe they do this for several reasons.
Sexual Competition
The most obvious reason male deer, known as bucks in the case of whitetail deer, grow antlers is to fight over mates. Anyone who lives around a lot of deer has probably seen or heard bucks fighting during the mating season, or rut, which is in the fall. This is because the bucks do so in dramatic fashion by clashing their antlers together and trying to push the other buck away.
Dominant bucks win these fights and drive competitors from their territory. They can then mate with more of the local female deer, or does.
Sexual Selection
Because antlers are associated with a buck’s strength and dominance, the does are attracted to them and use them to decide if they want to mate with a given buck. Because antlers require good nutrition and a lot of energy to grow, they also signal to the females that the buck is healthy, has good genes and has access to resources that will benefit them and their fawns.
Defense Against Predators
It is unlikely that antlers’ primary purpose is to fend off predators, especially considering does and fawns don’t grow them when they’re smaller and more vulnerable. Nevertheless, since bucks don’t shed their antlers until a month or two after the end of the rut and there have been documented cases of bucks fighting off wolves, bears and other predators with their antlers, researchers theorize that the antlers may serve a secondary purpose as a weapon for a buck who’s been weakened after the rut and following winter.
How Fast Do Deer Antlers Grow?
Deer antlers can grow at over a quarter inch per day or nearly two inches per week. This makes them the fastest growing bone among mammals.
Bucks shed and regrow their antlers every year. They shed the antlers in the winter after the rut sometime between January and March. Then, they start growing a new pair in April. This pair must be ready for the rut in the fall, so most bucks have finished growing the antlers and shed their velvet to reveal the hard, sharp bones at the end of August.
This means the buck has four to five months to grow their antlers. Meanwhile, his antlers will be around 30 inches tall with up to 200 inches of net length. That’s a lot of bone to grow in such short a time, which is why they grow so quickly.
Growth is most pronounced during the beginning of the cycle and tends to slow down towards August. During this period, the antlers will calcify and harden after which the buck will shed the velvet in preparation for the rut.
Does Age Affect Deer Antler Growth?
Age is one of the biggest factors that affects the speed and extent of antler growth. After a male deer is born in the spring, he will actually actually start growing antlers going into his first rut, but these will just be little bumps known as “buttons.”
The next year, when the buck is a “yearling,” he’ll actually grow recognizable spikes, though they’re still nothing compared to the giant racks of mature bucks, just about 25% of his genetic potential. For this reason, they grow a lot more slowly, around ⅛-inch per day.
We’ve tabulated this info in our article on when deer start growing antlers.
A buck usually doesn’t grow antlers that are a 100% of his genetic maximum until he is five or six years old. At this point, he’ll have to grow his antlers pretty fast, at least a quarter inch per day if not over half an inch per day.
While the buck stays healthy, he’ll continue growing his maximum antlers for several years. Nevertheless, like all mammals, his health will begin declining as he ages. A buck over nine years old, if he manages to survive that long, is an elderly deer, and he’ll most likely experience a slowing of his antler growth resulting in smaller antlers.
Other Factors Affecting Antler Growth
Antlers only grow at incredible rates like half an inch per day in optimal conditions. There are many other factors that may decrease the speed and size of growth.
Sunlight
Believe it or not, the deer antler growth cycle is actually dictated by the sun, specifically, the length of the day. As daylight increases going into spring, the bucks begin to grow their antlers. When the days start shortening again, they shed their velvet so they can fight with the full antlers during the rut.
Obviously the length of the day as a function of the season is a preset astronomical process far beyond your control. However, it does partly help explain why deer living farther north tend to have bigger antlers. The change in daylight is much more pronounced making the antler cycle consistent and reliable. Meanwhile, deer in the south, especially states like Florida, have less predictable cycles that can result in smaller antlers.
Hormones
The antler cycle is dictated by the length of the day, but at the biological level, it’s controlled by hormones, namely testosterone. Increased daylight causes testosterone levels to start rising, initiating the growth of antlers. Come fall, testosterone levels shoot up to their peak, making the bucks aggressive and territorial. When testosterone drops after the rut, the bucks lose their antlers.
If you’re managing a herd, hormones are also something not directly under your control. However, you can keep a healthy buck-to-doe ratio to maximize testosterone and antler health.
For purely wild deer, ratios skew heavily towards does, but you should try to keep a herd at a 1:1 ratio. As well as producing other positive outcomes like bucks who are healthy and not totally spent after the rut, a ratio heavier in bucks creates more competition, which will marginally boost their testosterone levels, leading to better antlers.
It’s also worth noting that testosterone levels increase with age into maturity, reaching their peak when the buck is five or six years old and only starting to drop off again when he’s eight or nine. To get bucks with high testosterone levels and big antlers, help them live that long.
Latitude
Besides the daylight factor, latitude affects antler growth due to something called Bergmann’s Rule. Basically, individual mammals farther from the equator are larger than those of the same species closer to the equator. This is because larger animals have a lower ratio of skin surface area to body size, so they retain heat more effectively.
Whitetail deer definitely follow this rule. The farther north you get, the bigger they’ll be, and this also applies to their antlers.
Nutrition
It takes a lot of nutrients and energy for a buck to grow antlers. For this reason, keeping track of your bucks’ antler growth is a good way to make sure they’re eating well. Specifically, there are three main nutrients to pay attention to.
- Protein: Antlers are about 40% protein, so a buck needs high-protein foods like soybeans, alfalfa and clover. In fact, protein should represent 16-20% of his diet.
- Minerals: The most important minerals for antler growth are calcium and phosphorus.
- Energy: It takes a lot of calories just for a buck to live. When he’s growing antlers, he needs extra. That means he needs access to high-energy food sources like grains.
Overall Health
Finally, a buck’s overall health will contribute to the size of his antlers and how fast he grows them. If he suffers from infections, parasites or excessive environmental stress, his body will have to focus on those problems over growing antlers, leading to smaller, less impressive racks. As a result, antlers are one of the best reflections of your herd’s collective health and well-being.
Management Means Paying Attention to Antlers
Many hunters ask “how fast do antlers grow” simply because they’re interested in getting the best decorations for their wall. While you definitely need to pay attention to the antler growth cycle in this case, its implications actually go far beyond mounts and can help you manage your herd. Keep an eye on your bucks’ antlers, their size and how fast they’re growing to better understand the age, nutrition and health of your herd.