Some people, during moments of introspection while watching their dog do dog things (ranging from basking in the sun to eating a dead rat), wonder, “How old is my dog? How can I determine the age of a stray dog?”
These questions may arise because the dog was adopted without knowing its birth date, or because you’re a bit scatterbrained and can’t remember.
Unfortunately, determining a dog’s age is not like with trees. You can’t cut them open, count the rings, and expect them to regrow. YOU CAN’T. DON’T DO IT.
Honestly, part of the reason we want to know a dog’s chronological age is to get an idea of their equivalent human age, and how many good years they have left.
You may have heard the rule that one dog year equals 7-8 human years. Many people learn this in childhood. And they spend half their lives misled. DON’T BELIEVE IT. IT’S NOT TRUE.
We promise this is the last time we’ll use caps lock. In this post.
How to Tell a Dog’s Age
First, not all dogs age the same. Small breeds generally live longer (and age better) than large breeds. A German Shepherd and a Yorkshire Terrier of the same age won’t look it.
For example, the Great Dane is one of the dogs with the shortest lifespan.
So, large dogs die sooner than small ones because they age faster. It’s believed their large size imposes an extra burden on their physiological processes, wearing them out more quickly.
Another detail is that large dogs are more vulnerable to cancer. If their bodies are focused on rapid growth, they lose resources for maintenance. Plus, more cells and cell turnover imply a higher risk of tumor development.
A University of Adelaide study has shown that large breeds have a higher early-age cancer death rate than smaller breeds.
They also don’t mature at the same rate. Though this process is a useful tool in determining the age of a puppy. Small dogs reach maturity before large dogs. It’s considered that giant breeds reach maturity at 2 years, while smaller breeds do so at 13-15 months of age.
On average, dogs’ social and sexual interest starts at 6-9 months, they are considered emotionally adult at 15-18 months, and fully mature at 3-4 years. Though many dogs choose never to show that maturity because they love chaos.
There are other physical traits that can give clues about an animal’s age. If you’ve researched these topics, you’ve probably read about determining a dog’s age by their teeth.
In most, from 12 weeks of age, temporary teeth fall out to be replaced by permanent ones. Full dentition is present by 6 months. For comparison, in human children, this process starts between 5 and 6 years and can extend to 10-11 years.
Again, in small dogs, teeth erupt later than in large breeds. Experts can estimate a dog’s age based on dental wear. However, it greatly depends on their diet and lifestyle.
A Dog and Genetics Blog
Possibly the most reliable way to determine a dog’s age is through the epigenetic clock. Also known as DNA methylation clock, it measures these levels to calculate age.
Over the years, methylation in our DNA, especially in CpG islands, areas of the genome with a high concentration of cytosines and guanines linked by phosphates, changes. By measuring these levels, you can estimate the individual’s age.
Over time, the epigenetic clock model has been improving, although using the human species as a model. An interesting advancement was GrimAge, a version that added environmental factors like smoking, and individual parameters like sex or chronological age to the calculation.
In 2019, a study came out that addressed this topic scientifically. “Quantitative translation of dog-to-human aging by conserved remodeling of epigenetic networks” is a research that sought to create a dog aging model, through the study of epigenetic changes, specifically methylation, and its comparison with humans.
The study involved 104 dogs with age differences ranging from a few months to 16 years. They confirmed that comparing the methylation of young dogs with young humans, and the same with older individuals of both species, there was a high similarity. Methylation changed with the age of the dogs just like in humans.
They managed to obtain a way to calculate a dog’s equivalent human age. Human equivalent age = 16 x ln (chronological age of the dog) + 31. For those not too savvy in mathematics, like me, ln is the so-called natural logarithm or Neperian logarithm (technically different concepts, but this isn’t a math blog). Therefore, a 2-year-old dog would be 16 x ln (2) + 31 = 42 years. For the paranoid, the ln of 2 is 0.693.
Problem solved? Not quite, but at least we have something. Although the study was done on 104 dogs, all were Labrador Retrievers. Considering that dog breeds follow different aging rhythms, this formula gives us an approximate idea, but especially in small dogs, it’s inaccurate.
Without going into too much detail, today it’s impossible to know a dog’s age with exact precision.
Even with genetics, we lack many details of their aging processes for it to be as simple as sending a saliva sample and being told their Chinese horoscope in a few weeks. We know because we work in this field.
In genetics, I mean. We don’t do anything with Chinese horoscopes.
If you want to see what we can teach you about your pet with genetics, you can check out our DNA kits at Koko Genetics.