The Truth About All The Broken Antlers

The two most common questions we are asked each year deal with antlers. Hunters want to know: Why are some antlers dark brown and others white? And why do we see so many broken antlers where we hunt? The answers to both questions really are inter-related and have a great deal to do with the demographics of the herd and their nutritional plane. Thus, a whitetail’s habitat, diet and social structure all play a role in their antler color and composition. In the following article, I’ll describe why that’s so.

ANTLER GROWTH & COMPOSITION

Let’s start with a primer on antler growth. Antlers evolved millions of years ago in the deer family, and they apparently served several functions. These functions include social display structures, scent dispersal organs and weapons for defense and male combat. Paleontological evidence of some modern deer descendants supports these conclusions. Whatever reason for their existence, the antlers of modern whitetails occur only on males, and we know their function is primarily for combat between rival males.

Whitetails grow and cast their antlers on an annual basis. As a general rule, each time the antlers increase in size until the buck reaches maturity (4.5 years or older). Antler casting is stimulated by the continued shortening of the day during late winter, as well as depletion of testosterone from the breeding season (rut). Cells called osteoclasts eat away at the boney connection between the antler and the pedicel protruding from the frontal bones until they fall off rather unceremoniously! Shortly thereafter, cells around the edges of the pedicel begin to organize for the coming antler growing season.

My observations support that the beginning of antler growth occurs around the middle of March in most of North America, when the length of day and night are the same. It has been proposed this causes a brief spike in testosterone, which stimulates the beginning of antler growth. There is a misconception that antlers are pre-formed as cartilage, then once the antler is formed, the cartilage turns to bone. However, actually there is a line of cartilage formed in the leading edge of the beam and tines, which then is converted to bone as the antler grows. This process is called ossification.

While in the growing stages, antlers are comprised of about 80 percent protein. However, protein levels are later reduced to about the same as calcium and phosphorus when growing concludes. If we analyze antler for its constituents, we will find protein in most of the antler as it is forming, then several minerals appearing as ossification. The largest proportion of minerals are calcium (19 percent) and phosphorus (10 percent), followed by manganese, barium, potassium, zinc, selenium, magnesium, iron, sodium, strontium and aluminum in much smaller amounts.

ANTLER COLOR

We conducted studies to answer why deer in some regions tend to have whitish antlers, while those in others have dark antlers. Scientific research helps answer this question. The color on antlers is initially created when the buck begins to strip velvet. It often is thought that bucks rub the velvet off their antlers, thereby obtaining stain from the trees they rub. However, this is only partially correct.

When the antler reaches maturity and the breeding season approaches, once again day length has a profound effect on the physiology of bucks. Increasing testosterone triggers the completion of antler growth, and the “burr” begins to expand around the base of the antler. Inside the antler base, bone cuts off the return blood supply from the antler core, while the burr shuts off the blood supply in the velvet. In a matter of minutes, the velvet begins to die and decay.

I have observed many times a buck feeding in a food plot with fully velveted antlers, then walk into the woods, to return less than an hour later with bright red antlers! There often are strips of decaying velvet hanging off the antlers, which other bucks in the social group may eat. It’s the blood spilled on the antlers that produces the initial staining, and stains from specific tree and shrub species later provide additional stain as the buck makes hundreds of rubs.

So, again why are some antlers stained dark, while others are whitish? We conducted a study in which we cut sections through the two types of antlers and measured the density of the outer layer of bone on these antlers. We found that the denser antlers tended to resist taking up stain, while the less dense antlers readily accepted staining. That makes perfect sense! We also noticed that the denser antlers were less flexible! Further, we noted that deer on poorer nutrition tended to have darker antlers.

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ANTLER BREAKAGE

So, does antler density have any connection to more broken antlers in some areas? After decades of deer research, it’s still hard to say. But here’s what we know. There are very few studies on why some geographic areas seem to have more broken antler tines and beams than others. One published study concluded there were no identifiable factors for broken antlers. There also have been proposals on the side of not enough mineral. It could be argued that deer diets deficient in calcium and/or phosphorus could lead to less dense antlers, which are more flexible and coincidentally resist breakage.

Yet, there is another side to consider. Researchers studying red deer in Spain reported that certain mineral deficiencies can increase antler fracturing, most notably manganese. Manganese is an essential nutrient, responsible for (wait for it) macronutrient metabolism and bone formation! A manganese deficiency is characterized by weakened bones. So, have we identified a “magic bullet” for reducing antler breakage in deer? Could fertilization be the key to reducing antler damage? The science just does not yet support such a recommendation, and it would be unethical for me to make such a recommendation. However, it’s plausible to say we may have a nutritional problem causing broken antlers.

Unfortunately, the answers to biological questions most often are not simple. During the last 30 or so years, I have been involved in managing deer herds throughout the species’ range. During this work, we have examined sex ratios and their impact on whitetail genetics and reproduction. Demographics is a critical element in deer management; one too often ignored by classical whitetail biologists. It is amusing how many states report their whitetail demographic makeup as “antlered and antlerless,” or consider any deer older than a fawn as an adult. Whitetails have a very complex social structure in which, if undisturbed, leads to a stable and less stressful population. Doe clans are strictly organized so that every individual in the group is related to the others.

The alpha doe is not going to allow another doe from an unrelated clan to enter her social group. Bucks develop smaller social groups, usually made up of pairs we label the dominant buck and subordinate, or “toady.” The next level of the buck social herd is made up of many of these “alliances.” These buck social groups grow up together and generally know one another. We have identified special bucks in the herd, we call “regulators,” whose job it is to keep the social peace in a specific area. In herds where the age structure of bucks has been skewed toward immature bucks, there is no such regulation. Every buck, no matter how young, has a chance to breed. Skewed sex ratios develop, commonly as poor as one buck to 4-5 does (some areas even worse). In such areas, there is very little fighting, and you seldom see a broken antler.

We started manipulating buck:doe ratios to see what happens as the ratio is tightened toward equal numbers of bucks and does. We discovered, as we moved from skewed buck:doe ratios to tighter ones, the amount of fighting increased substantially. We also noted that the percentage of broken antlers increased, as well! There was an excellent study conducted at Auburn University by Gabriel R. Karns and Stephen S. Ditchkof, entitled Antler Breakage Patterns in White-tailed Deer. They concluded, “The study provides a general description of antler breakage in a white-tailed deer herd and reaffirms that antler breakage is likely a byproduct of many interwoven individual antler, herd demographic, and environmental variables.”

FINAL THOUGHTS

My conclusion at this time is, the reason some areas have an apparently disproportionate percentage of broken antlers could be tied both to nutrition and the social structure and demographics of the herd itself. It is enlightening to consider that many of the areas where we see a large percentage of broken antlers, such as Kansas, also have more balanced buck:doe ratios! So, although frustrating as it is to have to pass up a huge buck with half his antler gone, it may be a positive sign that the herd at least demographically is in good shape.