Aging fast


A senior citizen by age four/Craig Medred photo

Leave it to science to mess up that belief your 4- or 5-year-old dog is in the prime of life and should be a top-level performer for years to come.

After tracking methylomes in people and a pool of Labrador retrievers, a team of researchers from the University of California San Diego has judged as so much hooey that old idea that one year’s in a dog’s life equals seven years in a human’s life.

Dogs, they say, mature much faster than was formerly believed and age rapidly through their first three years of life. By age four, the researchers contend, the average dog is beyond middle-age. The researchers put the animal in its early 50s in human years.

The study published earlier this month at bioRxiv, a preprint server, has yet to be peer-reviewed. But it’s been rocking the dog world with its observations on how fast dogs mature.

In the first three years of a dog’s life, it appears to be aging at a rate of 12 to 13 human-years per dog-year, but dogs do not age in a direct line, according to the study. They age on a curve which begins to flatten after age four.

Beyond that date, it takes the average dog another seven years to reach the human equivalent of 70. In this period, each dog year is equal to only about two and a half human-years.

Still what is most startling about the study is the suggested rapid maturation of dogs. Front-running Iditarod Trail Sled Dog Race competitors who seem to have been running younger and younger teams every year might have stumbled onto a simple reality of canine development.

The study puts a year-old dog at about 30 in human years. That’s about the age at which human marathoners have been found to peak with their top performance years considered to be between ages 20 and 35.

A 2013 study of Ironman Hawaii competitors also found them peaking slightly later. And the Ironman, which throws a variety of physical challenges at competitors, might be more like the up, down, wet, dry, wind-battered, sometimes-tough-trail Iditarod than a marathon on well-maintained roads.

After looking at 20 Ironmans, researchers reporting Extreme Physiology & Medicine in 2013 said, “the age of peak Ironman performance was 32.2 ± 1.5 years for men and 33.0 ± 1.6 years for women. . In Ironman Switzerland, there was no difference in the age of peak Ironman performance between genders for top-10 women and men from 1995 to 2010 . The mean age of top ten women and men was 31.4 ± 1.7 and 31.5 ± 1.7 years, respectively.”

If the UC-San Diego study is to be believed, the canine equivalent of a 32-year-od Ironman (or Ironwomen) would be about a year and a half.

chart of life

The study’s chart of dog years versus human years/bioRxiv

Not just dogs

Accidental discoveries sometimes being the most interesting part of science, it is worth noting the UC-Davis researchers weren’t really trying to sort out the old, old question of dog years to human years.

What they were trying to do was determine if methylomes – the markers left by the methylation that drives activity in the DNA that carries the genetic code of life for all living things – can be used to measure aging.

“Here, we map common epigenetic changes experienced by mammalian genomes as they age, focusing on evolutionary comparisons of humans to dogs, an emerging model of aging,” they wrote, and the “results establish methylation not only as a diagnostic age readout but as a cross-species translator of physiological aging milestones.”

The 104 Labradors in their study, they reported, displayed changes in both physiology and methylation that could be tracked and charted similarly to with humans.

“The observed agreement between epigenetics and physiology was particularly close for infant, juvenile and senior stages,” they wrote. “For instance, the epigenome translated seven weeks in dogs (0.13 years) to nine months in humans (0.75 years), corresponding to the infant stage when deciduous teeth erupt in both puppies and babies.

“In seniors, the expected lifespan of Labrador retrievers, 12 years, correctly translated to the worldwide lifetime expectancy of humans, 70 years. For adolescent and mature stages, the correspondence was more approximate, with the epigenome showing faster changes for dogs, relative to humans, than expected by physiological tables.”

Most dog owners, already inclined to think their canine friends age too fast, will probably be unhappy to read the news on rapid aging, but the study did suggest there might be something they can do to increase canine life expectancy.

If methylation patterns truly track the physiological progression of an organism’s life and not just chronological time, the researchers hypothesized, “the pattern should respond to interventions that slow or delay aging, such as anti-aging treatments.”

Two of those anti-aging treatments are well-documented in mice: dwarfism and caloric restriction. (The former is vividly notable in dogs with some small breeds having, on average, life spans two to three times longer than large breeds.)

“When applying the development clock to mice treated with lifespan-extending interventions,” they reported, “the epigenetic ages were 30 percent less, on average, than those of control mice. These same results were observed when using the development clock trained in dogs to predict mouse age. Together, these results demonstrate that the methylation states of developmental gene modules track the physiological effects of aging and aging interventions in multiple mammalian species.”

For science, the authors of the study claimed something of a breakthrough.

“Our study has demonstrated that the methylome can be used to quantitatively translate the age-related physiology experienced by one organism (i.e. a model species like dog) to the age at which physiology in a second organism is most similar (i.e. a second model or humans),” they wrote “These results create the opportunity to use the methylome not only as a diagnostic readout of age (as per the epigenetic clock) but for cross-species translation of physiological state. Such translation may provide a compelling tool in the quest to understand aging and identify interventions for maximizing healthy lifespan.”

For dog owners, the takeaway might be simpler:

Fido ages pretty fast already, and you’re not doing him/her any favors by offering extra treats. Every study out there has agreed that when it comes to keeping dogs healthy, it is better to underfeed them to overfeed them no matter how hard that might be to do given that many canines are world-class beggars.

And there is now evidence that underfeeding will help them live longer as well.















8 replies »

  1. “Dogs, they say, mature much faster than was formerly believed and age rapidly through their first three years of life.”
    This explains why most dogs running the Iditarod are 3 years of age or younger…just look at Mackey’s “champion” teams – puppies!
    We can only wonder where all the “old dogs” in Alaska wind up?
    We can also ask ourselves, if dogs age so quickly is it humane to make an “older” dog run 1,000 miles in a little over a week?

    • Maybe this will help Steve. Taken right off their website.

      Dropped dogs are dogs that are removed from the race for one reason or another. A dog that isn’t feeling well, has an injury, isn’t running well, is in season, or just doesn’t have the attitude to race, are ‘dropped’ at checkpoints along the Iditarod Trail.

      Veterinarians at each checkpoint are on duty to examine the dogs as they arrive or as they rest at a checkpoint. If a dog is dropped at a checkpoint, the veterinarians take care of the dog while the dog waits for a ride on a plane back to Anchorage. The musher’s team goes on without the dog.

      Dogs arriving back in Anchorage have a short stay at the Lakefront Race Headquarters Drop Dog Lot. Veterinarians are on duty. Vet techs as well as other volunteers, care for the dogs until they are picked up from the Lakefront dog lot. If a dog needs medical treatment, it receives it. Most dogs are in excellent condition when arriving at the Lakefront. That fact is verified by a complete post race exam by the vets at the dog drop area.

      Dogs rest comfortably on straw, sometimes covered in light blankets. They are cared for, fed, given fresh water, and receive lots of pets and loving from the drop dog volunteers and tourists visiting race headquarters.

      Dogs that can’t be picked up before nightfall, are taken to the ‘prison’ where they will be safe and well cared for during their short stay at that location while they wait for their dog handler or musher to pick them up.

      Once dogs are ‘home again at their kennel’ they resume the normal activities involved with living at their kennel. They get regular exercise, eat healthy meals, drink plenty of water, enjoy time with the musher, handler, and family, and dream about running the race again someday soon!

      • Bryan,
        I am not talking about “dropped” dogs in the race, just speaking of all the “old dogs” in general. (Associated with Iditarod dog lots)
        If K9’s reach their peak by age 3, that is a very short lifespan for 1,000 mile races.
        Sure, many “back of the packers” have older dogs, but what we continue to see is top competitors always have young dogs.

      • Well Steve, what is NOT happening to old sled dogs, is what PETA wants to do with them.

        While the rest of the world has gone to no-kill shelters and training for adoption of even difficulty animals … PETA remains the inconsolable & committed cold blooded killer. It is truly bizarre.

        It’s not mushing that heartlessly disposes of dogs. It’s PETA that’s jonesing for the gas chambers.

        The rest of us have known this for many years.

        Racing dogs younger is harder on the kennel & trainers, because it makes their dog & team turn-over higher & faster. It makes their job & life more hectic.

        But retiring dogs younger means they are far easier to place, and are suitable in a wider range of situations. There’s a lot more demand, and much more enthusiast demand, for the younger dogs. It’s probably a sellers market, and profitable.

      • In many situations in the wild, there is an urgent priority in getting the young up to speed as fast as possible. It’s a dangerous world out there for babies, and the parents are up against it pretty hard, to carry the extra burden.

        But that’s not a universal situation, and we see ecological contexts where growing up slower makes better sense. For example, old-time open-range cattle took 7 years to grow to market-size, where today that is under 2 years.

        Many animals have the range of variation to adapt pretty dramatically, in terms of growth rates and patterns of maturation. Dogs in the wild – wolves – actually control their fertility & reproduction, in response to opportunity and lack thereof.

        You could have dogs that peak later, that are ‘late bloomers’ … like many people. There is variation available in different breeds & types. These researchers here probably picked their target animal, in order to avoid the complications that exist.

      • So TED,
        All your anecdotes aside…
        Where are all the old sled dogs in AK?
        In a hole?

      • Sure they’re in a hole Steve, most of them. Old sled dogs don’t have long left, so we aren’t accumulating a big population of them; not as bad as Baby Boomers anyway. They die, and they’re buried or cremated.

        Some are good people-dogs, and adopt out readily. Some are good leader-trainer individuals, effective even in age in 2nd/3rd tier dog sports. Some are committed & useful yard-dogs, and stay happily on the chain until the end.

        Sled dogs, Alaska Huskies, aren’t a Breed. And as they’re Selected, tightly focused pro & con factors come into play. Anything else goes (pro or con), and that makes them more variable than a Breed. Any kind of ‘unusual’ in a Breed is a ding (good, bad or indifferent) … a call for the vet. But in a Husky, differences that otherwise don’t interfere with the goal, are just ‘color’.

        That makes it easier to send sled-retirees to a larger variety of post-competition destinations.

  2. My observation is that smaller dogs live longer and obviously age different than bigger dogs. Thaz my story and I am sticking to it. So, if that is tue case, how can this study be accurate?

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