Antler Growth and Drought

 Todd Black, Biologist with Utah State University Wildlife Extension provides this insightful look at how droughts can impact antler growth. This can be especially important information to consider when you have accrued many years of bonus/preference points for that trophy hunt of a lifetime and are planning your hunt.

“The past few years have been drought years, but I feel the springs have been wet and feed plentiful. It seems conditions don’t get poor until animals are hard horned. Yet, in some videos I’ve seen, they are talking about drought causing poor growth? Also, when do deer and elk hit their prime in antler growth and then start to digress.”

 Kevin

Thanks for the great questions Kevin—

The second part of your question regarding when ‘deer and elk hit their prime and then start to digress’ is really quite variable and depends on many different factors. However, the general rule of thumb that you typically hear and is supported by some research is that deer reach their prime in antler growth and maturity some where between 4.5 and 7.5 years of age. Often they will continue to get more massive and more points (if it has the genetic make up to do so) but maximum tine length typically occurs at some point during that three year period. Elk are a bit different—often peak tine lengths in elk can occur as late as 10-11 years but more often occurs between 6.5 and 8.5 years of age. Again, the bull will typically continue to grow mass and get more ‘massive’ as it gets older up to 12 and 14 years of age in limited and non-hunted areas. Having said this, there are many factors which may extend this growth and our definition of ‘prime’. Nutrition and genetics are just as important as what type of stressors the animal may occur throughout its life. How actively it will participate in the rut, where it fits in the dominance hierarchy, how many predators are in the area, how hard the area is hunted, where it lives, and what kinds of extremes it will encounter from the weather can all play a significant roll in how its antlers grow and when they will peak in growth.

To address your first question regarding antler growth, is a bit more complicated, hence all the confusion, theories, and tall tales we all hear. The truth is after many years and all the research done with ruminant animals, even on white-tailed deer, the nutritional needs that mule deer require to grow antlers still aren’t very well understood. However, there are a few things we do know with a fair amount of certainty.

First, in order to function and survive, antlered animals require nutrients from five groups just like us only a bit different. They are; 1–crude protein, usually 12-14% of their diet needs to be protein for optimal body maintenance and antler growth.  Any more than this is typically discarded and can often cause digestion and bowel problems.  2–energy (taken from digestible matter) the amount of energy or biomass a deer has to take in really varies from season to season and from location to location. In early summer a buck deer may only have to feed a couple of hours during the day where as in winter months it may be twice to three times that amount.  3–minerals (calcium and phosphorous) often overlooked and quite often lacking in the diets of many deer. This is why old salt and mineral licks are often dug down several feet in the ground. Deer crave these minerals and if obtained in sufficient amounts, can greatly affect antler growth. 4–vitamins equally as important as minerals but more readily available in the vegetative matter deer eat. 5—water, often water is obtained from vegetative matter and a big buck may only water once or twice a week depending on existing environmental conditions.  Often times during a drought mule deer have been observed eating larger quantities of evergreen drought-resistant plants. These plans usually have less available nutrients and energy and can take more energy to digest than the deer may obtain from these types of plans. Of these five basic requirements, protein, minerals, and energy are the needs that most typically would limit not only antler growth but rut activity and post rut recovery by the bucks during long winter months also can impact antler growth. These (protein, energy, and minerals) are obtained from the deers diet and the vegetation it consumes every day. Most deer require about one and a half-two tons of groceries per year to maintain optimum health know as ‘fitness’ and grow big antlers.

Second, we also know that nutritional needs of the antlered animals vary by season, geographic location, and species. Most of this variation can be contributed to the various physiological changes the deer may go through throughout the year. For a mule deer buck to grow big antlers, it is essential for the nutritional composition of the vegetation to be is optimum throughout the year.  During the antler-growing season (April—July), the vegetation must be high in proteins and provide essential vitamins and minerals.  During the late summer and fall seasons and even through early spring – the vegetation need to be high in carbs providing the deer with the needed energy levels to maintain and sustain its fitness throughout those long winter months.  If it isn’t ‘fit’ he will come into the antler growing season in sort of a nutritional deficit and it will require more food and more minerals and more energy to get him back to where he was coming into the winter. Similarly, if nutrition is poor in the summer months, he will come into the winter months in poor condition as well and the deficit could potentially even be bigger.

For nearly four decades, Dr. George Bubenik a professor of zoology at the University of Guelph zoology professor at the University of Ontario Canada like his father Tony Bubenik has been studying deer and antler growth and likely knows as much as anyone about the subject. He concludes that the three things most responsible for quality antler growth and growing big antlers are nutrition, genetics, and the lack of stress.  Research has shown that deer will produce smaller antlers the following year if they are under stressors from the lack of quality vegetation, water, hunting pressure, and pressure from the rut. These same bucks were kept at a lower level in the dominance hierarchy even though they were older bucks and bigger the previous year. Additionally, stress lowers the testosterone levels that are critical for good antler growth.

Third, prolonged periods of drought, like the drought periods we’ve seen in recent years, can have devastating effects on fawn survival and overall deer numbers over time.  On nearly all deer ranges in the western United States, the availability of green groceries is the most critical element in antler growth and development. We all know that overall, mule deer numbers are down largely because they are not in balance with available food resources. This lack of quality green groceries leads to inadequate nutrition and causes poor body conditions, reduced reproductive efficiency with the does, and often undesirable antler characteristics. Often with yealing bucks, the percentage or relative number of spikes is used as an indicator of nutritional conditions. The more spikes counted or harvested during a given year is usually a good indicator of a lack of green groceries. Continually high numbers of spike deer usually indicates a serious habitat issue and habitat deficiencies.

The executive summary is this—drought does effect antler growth. Precipitation directly effects vegetation growth and the quality of that vegetation. The nutritional quality of the vegetation will have a direct impact on the health and fitness of deer and elk and studies have shown that drought can reduce antler growth as much as 10%. That may not seem like a bunch but it takes a 200” record class buck down to a 180 class buck, still no slouch but it does have an impact none the less. The hardest part with regards to antler growth is we really can’t tell or predict how much a deer would or could grow from year to year even if conditions were optimal. Generally, the larger body a mule deer has, the larger its’ antler size; but feed intake per pound of body weight decreases along with overall metabolic rates during times of stress and drought.  I don’t recall any research being done or that has been done that would suggest that drought isn’t a major factor affecting the growth of antlers, especially if it occurs during the critical antler-growing season of April through July.

Another thing to remember is that the effects of antler growth are not always seen in the year the drought occurs, it may take a year or more of drought to adversely effect antler growth. Now having said all of that, remember that there are always exceptions. There may be certain individuals or localized populations that have adequate sources of water (springs etc. just as you mentioned) where the impact may not be as bad or even noticeable. I have noticed over the past few years, that the timing of what little precipitation that falls is equally important on antler growth.