The first signs that a dog is crossing over into his senior years are often a graying muzzle, cloudier eyes or a slower gait.
For dog owners, the aging of their four-legged companions has long been seen as something to manage as the physical and cognitive impacts become apparent. Walks get shorter, vet visits become more frequent, and it is understood that a dog will spend more of her day napping than out chasing a ball. Increasingly, though, there's a shift. Many scientists now see dog aging as something they can detect earlier -- and make interventions to slow -- rather than as a fixed inevitability.
"A topic that comes up constantly now is that we need to be more proactive," says Brennen McKenzie, director of veterinary medicine at Loyal, a biotech startup that is aiming to slow aging in dogs.
Searching for signs
Over the past decade, researchers have increasingly focused on finding indicators that offer clues about how well individual dogs will age and how long they will live.
In a recent study of blood samples from 937 companion dogs, U.S. researchers found that levels of certain small molecules in the blood -- produced as the body uses energy, breaks down nutrients and clears waste -- were linked with a dog's risk of dying during the follow-up period.
"We can actually predict whether a dog is more or less likely to die," says Tufts University researcher Daniel Promislow, an author of the study. He hopes that the work will open the door to quick and affordable molecular tests that help forecast disease.
Another area of focus is looking at routine blood-test results to deduce a dog's "biological age" -- a measure that reflects actual physical condition rather than the animal's simple chronological age.
In a 2024 study, researchers from Nestlé, which owns Purina, analyzed health records and lab results from 829 dogs. They found that dogs whose biological age was more than a year ahead of their actual age had a higher risk of death over the study period. The work, researchers say, can guide interventions designed to improve how long dogs remain healthy.
A quest to slow aging
As scientists get a better handle on how fast dogs are aging, they are also looking for ways to slow age-related decline.
Researchers have recruited dogs from the Dog Aging Project -- a long-running study involving scientists and research veterinarians from over 20 institutions -- to ascertain whether low doses of the drug rapamycin can improve heart health, mobility, cognition and lifespan in companion dogs. Rapamycin has been shown to extend lifespans in mice.
In this ongoing test, dogs are given rapamycin once a week for 12 months. Researchers say it is the first rigorous real-world test, in any species, of a drug designed to slow biological aging and extend healthy life. Positive results could pave the way for rapamycin's clinical use in apparently healthy dogs, says Amanda Coleman, a University of Georgia assistant professor who is one of the study's lead researchers.
Loyal, the biotech startup, hopes to make a drug that slows dog aging commercially available next year, pending conditional approval from the Food and Drug Administration. Its drug is designed to improve the body's sensitivity to insulin, the hormone that helps move sugar from the blood into cells to be used as fuel. Chronically high insulin can raise the risks of some cancers and dementia, and may contribute to muscle loss.
McKenzie compares cells to locks that with age can get "rusted and sticky" preventing their key -- insulin -- from working properly, which leads the body to make more insulin. Loyal's drug, he says, works like cleaning the rust out of the lock.
Loyal is also working on two other drugs, both of which focus on IGF-1, a hormone involved in growth and body size. Large dogs die sooner than small ones, and Loyal's theory is that breeding dogs to be very large has left some breeds with persistently high levels of IGF-1. After a dog is fully grown, the company believes the hormone may contribute to age-related disease and shorter lives. Loyal's drugs aim to lower IGF-1 later in life, after growth is complete, in the hope of helping large dogs live longer.
More immediately, researchers are also trying to give vets ways to consistently track mobility and physical function in individual dogs as they get older. In a Cornell study, 89 older dogs completed simple movement tasks -- including getting up and walking, stepping over low obstacles and moving from lying down to standing -- while observers scored their performance. The researchers concluded that vets could use such timed "up and go" tests to deduce whether a dog's physical functions are declining between visits.
While dogs' physical health has historically received more attention because its decline is so visible, cognitive dysfunction -- a range of conditions that some vets describe as dog dementia -- is now gaining prominence.
Earlier this year, an international working group of canine-cognition experts published guidelines to diagnose and monitor cognitive dysfunction. The AKC Canine Health Foundation -- which partly funded the work -- says owners should watch for unusually withdrawn or clingy behavior, staring at walls, confusion in familiar places and restlessness at night.
Because those signs can overlap with other issues common in older dogs -- like pain, failing eyesight and hearing loss -- diagnosing cognitive dysfunction depends on looking for a broader pattern of behavioral change and ruling out other causes, rather than relying on any single symptom.
To keep dogs diagnosed with dementia safe and comfortable, the Canine Health Foundation recommends that owners implement consistent routines, offer nighttime potty breaks, block unsafe areas, and add puzzle feeders and night lights, among other coping mechanisms.
There is some indication that exercise may help stave off dementia, although causality is unproven. A 2022 peer-reviewed study of 11,574 dogs aged six to 18 years concluded that more physically active dogs had fewer current signs of canine cognitive dysfunction. Another study that year found that dogs fed once, rather than multiple times, a day scored lower on a scale used to assess cognitive dysfunction. They were also less likely to have gastrointestinal, dental, orthopaedic, kidney, urinary, liver or pancreatic problems.
Back to basics
When it comes to lifespan, restricting calories may be one of the best things an owner can do. In a long-running Purina-backed study published in 2008, researchers followed 48 Labrador retrievers and found that dogs fed 25% less than their litter mates lived a median 1.8 years longer, and developed some age-related diseases later. Other studies since have confirmed the link.
Beyond moderating calories, age-old advice aimed at keeping dogs healthy into old age, including staying current on vaccines and preventive care, and keeping dogs mentally and socially engaged still stands.
While it is well known that owners should exercise dogs regularly, Stephanie Montgomery, a veterinarian who heads the American Kennel Club Canine Health Foundation, says exercise should be modified with age.
"Taking a dog out and doing a slow walk and letting them sniff is really mentally stimulating," she says.
Sniffing may benefit dogs' welfare in other ways too. In a small 2019 study, pet dogs trained to search for hidden food using smell became quicker to approach an ambiguous test bowl, a response researchers interpreted as a sign of greater "optimism" and improved welfare.
Among the more effective preventive measures owners can take to protect dogs as they age is regular brushing. Dental health, vets say, is often neglected because owners see it as cosmetic -- but dental disease can lead to chronic inflammation with impacts throughout the body. Making a habit of brushing can prevent needing to put an older dog under general anesthesia just so a vet can clean the pet's teeth.
"You're kind of rolling the dice," says Montgomery. "There's always a risk with anesthesia."
Write to reports@wsj.com.
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