Chances are you’ve heard the dog-years-to-human-years tall tale about dog aging: “One year in a dog’s life equals seven in human years.” Despite the continued efforts of veterinarians over decades, that fallacy persists.
It’s unclear how the “1- equals-7” calculation was derived. My guess is that sometime during the past 100 years, folks observed that many dogs lived to be about 10 to 12 years of age. These were likely larger dogs living outdoors with little, if any, medical or preventive care. They reckoned that since people lived to be about 70, that made for a simple equation of dog years to human years. Only it’s not that simple.
How does a dog aging chart work?
I was part of a team that developed one of the first pet aging charts in 1999. We reviewed the latest research on aging and worked hard to gain scientific consensus. Ultimately, we created the age tables that continue to serve as the template for more modern charts. We began by dividing dogs into four size categories (cats only needed one) since smaller dogs tended to live longer. We then applied a variety of biological metrics and data to calculate canine years into an equivalent human age.
In simplest terms dog years to human years is:
- 0-2 years old: of a dog’s life roughly equals the time humans take to reach adult size or post-puberty
- 3 years old: dogs are in their human-equivalent early 20s
- 7 years old: small and medium dogs are about in their mid-40s, while large and giant breeds are in their 50s.
- 13 years old: The biological fact (although we don’t fully understand why) is that dogs weighing over 50 pounds age relatively faster than small and medium breeds, making a 13-year-old 50- to 90-pounder equivalent to about 82 years in human terms, while a similarly aged, under-20-pound pooch is a youthful 68.
You can spot the many problems with using human aging and life expectancy to categorize growing older in other animals. The underlying genetic, physiological and even psychological differences and stages are challenging to compare. The truth is that aging is largely species-specific, and we’re making our best scientific guesses with these charts.
Because older dogs have different health requirements and an increased risk of many diseases, knowing when a pet is senior is essential to providing the best care. Veterinarians have used these dog age charts to wellness plans, nutritional recommendations and diagnostic test protocols for the past three decades. And they’ve worked pretty well.
How old is your pup: the 5 dog life stages
Birthdays, charts and genes aside, you may wonder what’s the big deal about a dog’s age. As all living things march toward the inevitable unknown, we can prolong our dog’s journey and make it more enjoyable by making lifestyle adjustments based on their aging biology. Veterinarians call this “life stage medicine.” It refers to doing things differently as a dog progresses through the five phases of life:
While at first, you may think this is ridiculously obvious: “Of course, old dogs need special care!” What’s not so obvious is at what age your dog becomes old and what special care is beneficial. That’s why dog age charts based on body size and biological age tests can help inform you on the most effective and restorative care for your dog. More importantly, you can enhance the later years by making healthy changes during the early transitions of life.
The best way to illustrate this is to examine a few examples of life stage care in action.
Puppyhood is the progression from birth to adulthood, marked by musculoskeletal maturity, full size, puberty and the ability to reproduce. For small dogs, this is usually birth until about a year of age, and for larger dogs up to 18 to 24 months.
Puppy life-stage care aims to:
- identify genetic or inherited disorders through DNA tests and exams
- prevent infectious diseases through vaccinations
- treatment and protection from parasitic infections
- spaying or neutering
- a diet formulated for growth
Most puppies must visit their vet every three to four weeks for the first four to eight months of life.
Young adult dog
The young adult years are the time to establish — and maintain — healthy habits. This stage is 1 to 5 years of age for small dogs and around 4 for larger dogs.
- Weight gain is common during these years, so watch your feeding and treat habits.
- Behavior issues may become problematic at this age, so be sure to work with your vet team on training, especially during the first couple of years of life.
- Heartworm, flea, tick and intestinal parasites preventives are administered monthly
- Exams with appropriate diagnostic tests and vaccines are needed every six to 12 months.
Mature adult dog
In human terms, “mature adult” refers to the 40s until about 70. For small dogs, this is approximately ages 5 until 12 or 13, and for large dogs, up to about 10 or 11. This is the period of life when poor lifestyle choices begin to cause problems.
- Health issues appear. Obesity and poor body condition often lead to early arthritis, high blood pressure, kidney and liver issues, diabetes, and even cancer around this life stage.
- Mature adults should be examined twice a year, along with routine blood and urine tests to detect the earliest signs of disease.
- Proper vaccines and preventives are critical because even minor infections can become severe in mature adults.
A dog’s last quarter-life is called the senior years. The senior life stage is also when canine size variations become more apparent and impactful, and age charts differ. For example, a 12-pound Dachshund attains senior status on some charts at age 14, while others define it at 10. (For the record, I go with 14.) On some charts, an 80-pound Lab earns his senior dog title at 8 while others wait until 11. The senior years are time to upgrade your pet care. Senior dogs should:
- Be examined twice a year
- Have a few more blood and urine tests to uncover hidden diseases
- Change to a senior-dog diet, and potentially add supplements, especially omega-3 fatty acids for anti-inflammatory properties, glucosamine for joints and other antioxidants.
- Larger dogs should have X-rays of the hips or other at-risk joints.
This is literally the last chance to diagnose illnesses early to improve outcomes. Hopefully, you started these healthy habits from a young age, and your dog will cruise into this phase full of energy, ability and vitality.
End of life for dogs
While no one likes to think about it, at some time in the future, your dog will require end-of-life treatment. These days, several ways can provide compassionate care at home. When your dog reaches this stage, have an open conversation with your vet about the best way to proceed based on your and your dog’s needs.
Leave it to science to challenge our trusty dog-age charts. The actual timekeeper of life is found in DNA, and the calendar age may not mean as much as once believed.
Scientists call it the epigenetic clock. As humans, dogs, cats and other mammals age, changes occur in their DNA. These changes can be measured using a DNA methylation level test. While researchers don’t fully understand all the factors that cause DNA methylation, many labs use it to calculate biological age. If the theory holds up, and it’s been around since the 1960s, with more attention brought to the subject in the 2000s, a dog or human’s biological age is a more insightful factor in health and life expectancy than blowing a clump of candles out.
Several companies are beginning to offer these biological age tests for dogs (some use telomeres to test and some use DNA methylation). While I’m still skeptical about using these tests to determine a dog’s “actual age” or rely on them to make birthday plans and medical decisions, I think they hold tremendous potential to identify premature aging and encourage lifestyle changes. Because many hidden diseases and inflammatory processes (I’m looking at you, obesity) go unnoticed until illness develops, these tests could prompt dog parents to adopt healthier lifestyle choices and medical interventions to extend life expectancy.
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