How do deer grow antlers so quickly?
The science behind antler growth, sheds, and velvet.
This story originally published on outdoorlife.com
When you stop and think about it, antlers seem like the stuff of science fiction rather than real life. They’re bones that grow extremely fast outside of a mammals body, and every year they fall off and grow back. For whitetails, at the peak of development, antlers will grow a ¼ inch per day; for bull elk it’s more like an inch.
To put that in perspective, imagine that one spring morning, you woke up and had two bones growing out of your forehead. In about a week, they would be 7 inches long, and two weeks later, you’d be knocking into every door frame you tried to walk through. While there still is a lot to learn about antlers, here are some of the secrets behind how antlers grow and what it takes for them to get so big.
Why Do Deer Have Antlers?
Before diving into the nitty-gritty of antler growth, we should get one thing straight. Whitetails, mule deer, elk, moose, caribou, and many other antlered animals across the globe are part of the same deer family, known as Cervidae. Male “cervids” (as well as female caribou) evolved to have antlers, and unlike horns, antlers are made of bone and are shed and grown back every year in a continuous cycle. For a large part of the year, they are made up of living tissue whereas horns are made of dead, fingernail-like tissue called keratin and remain attached to the animal year after year.
That the reason cervids have antlers is for mating purposes. Because they live in competitive societies and mate like spring breakers, males need something to work out their differences with and attract the ladies. Big pointy antlers are just the ticket, and while it’s important to note that they aren’t trying to kill each other, deer, elk, moose, and other cervids spend their respective mating seasons using their headgear to duke it out for cows or does.
What Causes Antler Growth?
The short answer is a combination of nutrition, genetics, and age, but it’s a little more complicated than that. The perfect combination of these factors is still hard to track, but when the formula is right, a buck or bull’s antlers will grow abnormally large. Here’s a breakdown of how the big three factors for antler growth work:
The better the habitat, the bigger the antlers will be at any age. As a general rule, protein-rich forage contributes immensely to antler growth. According to the MSU Deer Lab and a study from Texas, on a 16 percent protein diet, bucks consistently grew antlers that were twice as big as bucks on an 8 percent protein diet. In four years, the bucks that had more protein were sporting racks that scored 20 points higher on the Boone and Crockett scale.
Local native forage varies depending on where you hunt, and in some cases, agriculture and food plots play the most significant role in local deer diet. In terms of wild, high-quality forage some examples cited by the QDMA are blackgum in the north, beggar’s lice in the south, and partridge peas into parts of the Midwest. Of course, acorns and other mast are great across the board.
Seasonal changes and rainfall will affect the levels of protein in forage and, as stated above, supplemental feeding is often used to support antler growth.
This one is thrown around a lot at deer camp, but it’s a tricky thing to define in the wild. While it’s easy to think about big-racked bucks producing more big-racked bucks, the devil is in the details. Nutrition and habitat both impact growth regardless of genetics, and unless you are selectively breeding deer in captivity, it’s hard to tell what is doing what.
What we do know is that, just like other animals, genetics are a two-part equation, and both the mother and the father play equally important roles. Genetics will determine the shape and size of the antler, and studies have shown that big antlers are hereditary (more on this later).
However, the other external factors impact antler growth so greatly that it’s not the best thing to focus on. The upshot: small deer in your area are most likely not genetically inferior, they’re probably just be coming up short on the other two factors, age, and nutrition.
Before a buck can be called a monster, a hawg, a toad, or booner, it has to survive a few seasons. Simply put, dead bucks can’t grow antlers. Like the best things in life, antlers get better with time. A whitetail buck will reach generally reach his prime in four to six years, and for elk, it is more like eight to twelve.
Age is one of the easiest factors humans can manipulate to see bigger antlers. Regulations like point restrictions and deer camp customs like passing up smaller bucks can be helpful. But to do this on a large scale, well, that’s the subject of another article.
How Do Deer Antlers Grow?
Male cervids have two soft spots on their skulls called pedicles. In the spring or early summer, two nubs form at the pedicles and are covered in a sensitive type of skin called velvet. The velvet is packed with blood vessels that rapidly bring blood, oxygen, and nutrients that the antlers need for growth. The antlers grow from the tip, starting as cartilage and then calcify into hard bone as they go.
During the velvet stage, cervids try to avoid contacting their antlers with just about everything. Injuries to velvet during antler growth can cause changes. Abnormalities, and injuries to other parts of a deer’s body, such as the leg, can affect antler growth too. Once the antlers are fully grown, the velvet is cut off from the blood supply, and it dries up and dies before getting rubbed off by the animal. By the time the rut kicks off, a deer’s antlers are actually dead bone. Throughout the season, the connections between the pedicles and the antlers weaken, and usually during the winter, well after mating, the antlers fall off. In a matter of weeks, the cycle starts all over again.
Depending on the photoperiod, or amount of sunlight during the day that a male cervid is exposed to, they will either be growing or shedding their antlers. Generally, the more sunlight there is, the more the antlers will grow. The change in light triggers the pineal gland to tell the pituitary gland to release more testosterone. With the boost in testosterone, deer antlers can grow up to two inches per week, and in some cases, bull moose can put on a pound of bone per day during the peak of their growth cycle. Here is a general timeline of the antler growth cycle, although, depending on the area or species, the exact months may differ. (For example, moose don’t start growing new antlers until roughly two to three months after shedding.
Deer Antler Growth Cycle
April through May (Spring)
Antler growth begins from the permanent bases on the male cervid’s skull. It is slow to start, growing from the tip out.
June to July (Mid Summer)
With the increase in sunlight, growth increases rapidly. The buck or bull’s energy is focused on growth.
September (Late Summer)
As fall draws near and the days get shorter, growth slows. The antlers become mineralized, harden up, and blood eventually stops flowing to the velvet. The velvet dries, and afterward, it takes about 24 hours for a buck or bull to shed his velvet.
October-December (Fall to Winter)
The hardened antlers are now dead bone, and at this point bucks or bulls use them for the things that they do best during the rut: rubbing trees, fighting, showing off to females, and getting into all sorts of trouble.
January-March (Late Winter to Early Spring)
Male cervids can only maintain a connection between the pedicle and the antler when testosterone levels are high, so as daylight hours dwindle, levels taper off, the connection weakens. Eventually, the antlers are shed, and without them, the pedicles are open wounds. Scabs form, and in a matter of weeks, antler growth begins again.
The Cost of Antler Growth
Two fast-growing bones on your head are going to cost something, and for deer, elk, and other cervids this cost is huge. Protein from food is, of course, a factor and is a reason that nutrition is so important for healthy antler growth, but there’s another process, more to do with minerals, that takes the concept of recovery to another level.
It’s called mobilization, and it has to do with nutrients being drawn from other bones to supplement antler growth. The MSU Deer Lab sums this up best on its website:
“During mobilization, calcium and phosphorus are ‘mobilized’ and transferred from skeletal sites, such as rib bones, to be used in the production of antlers. The skeletal sites are replenished later through dietary intake.”
In other words, to grow their antlers so fast, whitetails and other cervids need to borrow minerals like calcium and phosphorus from non-weight-bearing bones. This takes an incredible amount of energy for something that is not exactly essential for reproduction, and when you stop and think about it, it’s amazing that so much of a male cervid’s life revolves around acquiring nutrients and minerals to grow his antlers and then recover.
After the growth is complete, they have to replenish those minerals from somewhere, and while the role of vitamins and minerals in a deer’s diet is still being studied, it is known that the soil plays a big part. Soils with poor mineral content, make it harder for recovery, and in a lot of cases where soil quality is low, supplemental feeds help to make mobilization a little more efficient.
One More Thing About Genetics and Antler Growth
Researchers at the MSU Deer Lab have done a lot of work around whitetails and antler production, and one of the lab’s recent studies explores nature (genetics) vs. nurture (nutrition) and the potential for genetically smaller bucks, from areas lacking in nutrition, to grow larger antlers. As stated above in the section outlining factors for growth, the only way to really dive into the role of genetics is to control the environment and nutrition of two or more genetically different deer. MSU did just that in this study.
Researchers took pregnant does from three distinct regions of Mississippi that represent different genetics, the Delta (a lot of nutrients and genetically large deer), Thin Loess (less agriculture and slightly smaller deer), and LCP (genetically smaller deer with poor nutrition).
The plan was to feed the male fawns from the does the exact same high-nutrition diet and see how they grew in captivity. If the smaller deer remained small and the genetically bigger deer remained large, then it could be said that genetics, regardless of nutrition, can hold back the growth of body size and antler size. If the smaller deer grew as large as the others, then nutrition would surpass genetics as the most important factor for growth.
While body size in the first generation remained somewhat consistent to their respective regions, antler size did increase. However, the study took a really interesting turn when the bucks fathered another generation of deer in captivity. The second generation was much bigger than the first, and there was a huge jump in both antler growth and body size. This was especially the case for the genetically smaller deer.
This phenomenon can be explained through something called epigenetics. While the DNA sequence in deer remains the same, environmental conditions cause small changes, and over generations, those changes will alter the expression of the genes. In other words, deer are not only a product of their immediate environment but a product of their parents’ and grandparents’ environments too. From the MSU study:
“One way to think about it is a series of switches within an animal’s genes. If generations of a family have lived in a low-quality habitat, then it’s advantageous to ‘turn off the switch’ for the genes that promote a large body and antlers—the advantage is that smaller animals are better suited to the quality of forage in their environment. This ‘off switch’ keeps animals from growing larger in a particularly good year, only to be hurt when forage quality returns to normal.”
This is how animals naturally adapt to their environment and what we see in the quality of our deer is representative of that generational adaptation. If there isn’t a lot of food around, it’s not good to be big, so the genetics adjust for this. Because of the incredible amount of energy it takes to grow antlers, they will remain smaller as well. It takes a generation or two of proper nutrition and habitat to really “switch on” the code for antler growth that lies within the DNA of all cervids.
So, in a way, yes, genetics do play a big part in antler growth, but the idea that genetics are set in stone to produce small deer is not exactly true. Manage the land accordingly, and in a few generations, smaller cervids could grow exponentially bigger.
What All of This Means For Hunters
Big antlers, in a way, are an indication of good health in the herd. To get through the stress of growing antlers all while being chased by predators, deer, elk, moose, and other cervids require high-quality habitat. In landscapes that don’t provide enough nutrition, they will adapt genetically to require less food, and consequently, antlers and body size will be smaller. A couple of things that we can do for better antler growth and better overall health of our cervid populations is to make sure that there is enough forage and a good ratio of animals on the landscape.
It’s important to think about antler growth generationally and not in terms of a quick cause and effect like putting out mineral supplements and immediately seeing results. The steps we take year after year to improve habitat, whether it be on private or public land, eventually yield results–it just takes years. So, the next time you look at that wall hanger, think about what went into growing those antlers, and think about how we can keep it all going for the next generation.