There are two methods hunters can use to estimate the age of harvested deer, and both rely on deer teeth. There is a lot of misunderstanding, misapplication, and misinformation shared about these valuable deer management techniques, so let’s look at the facts about how the two deer aging methods work, which is better in different circumstances, and how they compare against each other in accuracy.
Why Age Deer?
Why do wildlife biologists and deer hunters want to age deer? Doing so allows comparisons of harvest data within sex and age classes. It allows you to determine appropriate harvest strategies, enhance herd health, and track progress of your management efforts. It’s also fun and extremely rewarding to age a buck or doe you harvested, especially when the animal is fully mature.
Case in point, my young daughter shot a doe that aged 13½ years old! We celebrated the doe at the moment of harvest, and we celebrated again when we saw the jawbone and received the cementum annuli (CA) report. Not to be outdone, her younger brother shot a doe a couple years later that CA aged 14½ years old!
It is amazing to learn the incredible survivability of these animals in an area of high hunter density, high antlerless harvest, and high deer-vehicle accidents. Aging those deer added immensely to our memories from the hunts and provided additional knowledge about the local deer herd.
Deer Aging with Tooth Replacement
There are two methods for aging harvested deer. The first is tooth replacement and wear (TRW), also known as the “Severinghaus technique” after deer researcher Bill Severinghaus who developed it in New York in 1949. This technique is based on two processes. Tooth replacement is the process of gaining additional teeth over a deer’s lifetime and replacing temporary teeth with permanent ones. Tooth wear is the process of tooth erosion over time with age.
Whitetails are born with three temporary teeth (premolars) in the back of their jawbones. By 18 to 20 months of age, they replace these temporary premolars with permanent ones and gain three more permanent molars. All whitetails 18 months and older should have six permanent teeth on each side of their lower jaw. Fortunately, we can distinguish between the third temporary and permanent premolars by counting the number of cusps. Temporary premolars have three cusps while permanent ones only have two. The last cusp of the last molar also becomes fully erupted at two years of age.
This means that as long as you can count to six and recognize when teeth are fully erupted, you can accurately age fawns, yearlings (1½ years old) and all deer “2½-plus” with 100% accuracy – without ever looking at tooth wear. That level of accuracy is well worth the time necessary to learn the technique. The National Deer Association offers an excellent poster that explains the technique, and we also teach it at our Deer Steward courses.
Deer Aging With Tooth Wear
Once a deer is at least 2½ years old, we use the second half of the technique, tooth wear, to estimate whether the deer was more likely 2½, 3½, 4½ years or older. This is where the subjectivity arises.
Deer teeth have a dentine core covered by enamel. Dentine is dark and enamel is white, so as deer age they wear their teeth down and expose more dentine. The amount of exposed dentine on each molar allows us to estimate whether the deer is more likely 2½, 3½, and so on. This is fun, and it is a valuable management aging technique, but unlike the tooth replacement half, it is not 100% accurate.
Research by Aaron Foley and colleagues at the Caesar Kleberg Wildlife Research Institute in Texas published in December 2021 showed tooth wear accuracy on 134 known-aged adult bucks (2½ or older) was only 43-51%. However, accuracy improved to 87% for estimates within plus or minus one year of the actual age.
The high accuracy within one year of the actual age shows this aging technique is still valuable and useful for deer hunters.
Deer Aging With Cementum Annuli
The second aging technique is CA, and it involves using a microscope to count the growth rings in a stained cross section of the cementum that forms on the roots of a deer’s incisors (the small teeth in the front of a deer’s lower jaw). Cementum was first discovered in 1835 and has been used to estimate deer ages since Canadian researcher Frederick Gilbert published a paper in the Journal of Wildlife Management in 1966.
In short, mammals deposit cementum over the roots of their teeth. This forms layers similar to tree rings that can be counted to estimate age. Cementum rings correlate to seasons and are darker in winter when resources are scarce, so areas that experience distinct seasons tend to have higher aging accuracies than areas with more tropical climates. Professional CA technicians suggest an east/west line running through southern Missouri is a good demarcation for distinct cementum rings. This suggests CA aging for whitetails in the South is not as accurate as for deer in the Northeast, Midwest or Mountain West.
The CA technique has been used to estimate ages of mammals ranging from fruit bats to bobcats to bears and, of course, deer. Unlike TRW, you cannot use CA analysis in the field, on your tailgate or at camp, and it is not free. You have to carefully remove the middle two incisors, send them to one of three commercial labs in the United States, wait an average of one to three months for results, and pay a minimum of $30 for each deer.
Testing the Accuracy of the Methods
Is it worth the money for a CA age estimate? In 2000, Kenneth Hamlin and his colleagues at Montana Fish, Wildlife & Parks used samples of known-aged elk, mule deer and whitetails from Montana to test this. Cementum annuli estimates at Matson’s Lab were 97, 93 and 85% accurate for elk, muleys and whitetails. Not perfect, but the same study showed only 43% accuracy to the exact year for whitetails using TRW.
More recently in 2020, Iowa State University researchers submitted incisors from 473 adult bucks harvested in Iowa to Matson’s Lab. These were wild deer, so exact ages were not known, but the researchers studied precision of the CA estimates by submitting two incisors from each buck in separate mailings over multiple years. Matson’s Lab did not know which teeth were matched sets, so they aged all teeth independently. The results indicated the ages agreed within one year for 99% of the matched sets. That’s pretty precise!
This same Iowa State project estimated ages for 1,292 adult bucks using both TRW and CA methods. The researchers concluded TRW is superior for separating yearlings from adult deer 2½ or older (remember, TRW is 100% accurate for these age classes), and CA is better for aging deer that are 3½ or older.
Back to Aaron Foley’s study. They found CA accuracy for 134 known-aged deer 2½ or older was 60-62% for the exact year and 93% within one year. Their work also showed CA was better for older deer. It is important to remember, CA analysis is likely not as accurate in South Texas where the research was conducted as it is for deer in the Northeast, Midwest or Mountain West, so the reported accuracies are likely minimum estimates.
What About Soil Types or Food Quality?
Many hunters argue deer in areas with more sandy soils wear their teeth faster, or deer in droughty areas eat more woody browse and wear their teeth faster, or deer consuming abundant supplemental feed wear their teeth slower. Additional research by Aaron Foley showed all these assumptions are false. They found soil, drought and supplemental nutrition had only minimal effects on tooth wear and not enough to change the age estimate by more than a year off the actual age.
Head to Head Comparison
Neither technique is 100% accurate for all age classes across the whitetail’s range, but this does not mean these techniques are “not accurate,” as you’ll hear some misinformed people claim. You simply need to know the best applications and the limitations of each method.
Tooth replacement and wear is 100% accurate for classifying fawns, yearlings, and all deer “2½-plus.” Once whitetails reach at least 2½ years, tooth replacement and wear is then pretty good (87% accuracy) at aging to within one year of the actual age, and cementum annuli is even more accurate (93%). Plus, cementum annuli’s reported accuracy was measured from an area with minimally distinct seasons, suggesting a similar research project from a more northernly locale would produce even higher accuracy ratings.
I am a huge fan of estimating age of whitetail bucks on the hoof using body characteristics. That is fun but far from an exact science, and nowhere near as accurate as using teeth from harvested deer. In my opinion, both tooth replacement and wear and cementum annuli are extremely valuable aging techniques that add immensely to personal hunting experiences and deer management programs.