Sometimes it seems as if one day our dog is in the prime of life, and the next day they’re old. With others, age sits lightly on their shoulders and they are often mistaken for much younger animals. Whether it’s sudden or slow, though, aging is inevitable.
No one would argue that dogs live long enough. Their comparatively short lifespans—usually ranging from 10 to 20 years—are the painful thorn in the rose that is their companionship.
But scientists are turning their attention to uncovering the secrets behind pet aging. The answers they find could not only help dogs but also humans live longer lives. What we know now, though, can help our doggos stay well throughout their golden years.
WHAT AGING LOOKS LIKE
The age when a dog is actually considered senior or geriatric varies. Factors that affect onset include species, breed and size, but right now no quantitative measurements exist, unlike in human medicine, where geriatricians can make functional measurements of health and frailty.
“It’s all very qualitative,” says Matt Kaeberlein, Ph.D., director of the Healthy Aging and Longevity Research Institute at University of Washington in Seattle and codirector of the Dog Aging Project, which launched two years ago. “I think veterinarians are pretty good at looking at dogs and giving them an exam and saying in general this dog is healthy or not. It would be nice to have sort of quantitative measures as well to start to define some of these things.”
Most often, changes in appearance, movement, or behavior signal the onset of the canine golden years. Visible signs of aging include a frosted face, stiffening joints, and cloudy eyes. Pets may sleep more, slow down on walks, or not want to walk as far. Senses of smell and sight can diminish.
Internally, organ function begins to change. The heart and kidneys are often the first to decline. Outward signs of deterioration in those organs include increased panting, decreases in activity level or appetite, or an increase or decrease in thirst. Pain from arthritis and dental disease can affect dogs and cats.
Dogs who are aging successfully, on the other hand, maintain health, functionality and quality of life for as long as possible. They’re free from chronic disease and disability and have a good activity level. Keeping them that way is a combination of good veterinary care, nutrition, exercise, and genetic luck.
HOW AGING HAPPENS: THE INSIDE STORY
Why some animals seem to age more rapidly than others is in part associated with size. Small dogs tend to live longer than large or giant-breed dogs. That difference is one of the questions to which researchers are seeking answers.
“We don’t know 100 percent why big dogs age faster than small dogs,” Dr. Kaeberlein says. It’s suspected that a variance in chemical signaling by a hormone called insulinlike growth factor 1, or IGF1, plays a role. Hormones like IGF1 are involved in regulating development and physiology, and the size of large dogs is related to an increased amount of signaling by it that triggers changes or processes in cells.
From simple organisms such as fruit flies to mammals such as mice, studies have shown that animals with mutations that reduce IGF1 levels age more slowly and live longer.
“While it doesn’t prove causation in dogs, I think it’s pretty strong evidence that a major determinant of why big dogs age faster than small dogs is because of IGF1 levels and the amount of signaling through this pathway,” Kaeberlein says.
Other hallmarks of aging occur at the molecular and cellular level. The ends of the chromosomes, called telomeres, start to shorten. Mitochondria, which are like tiny engines inside cells, begin to decrease in function.
“Our ability to repair all of the damage that is constantly happening in our cells decreases as we get older,” says Daniel Promislow, Ph.D., professor of biology and professor of laboratory medicine and pathology at the University of Washington and codirector of the Dog Aging Project. “Dogs provide us with a terrific opportunity to ask how those molecular changes differ between long-lived and short-lived individuals within the same species.”
While the research has not yet progressed far enough to provide definitive answers, it is producing interesting data. Some things recapitulate what is already known from previous studies; for instance, that large-breed dogs in general are more likely to get cancer. But one trait in particular that is striking is that based on owner surveys, there’s a clear trend showing cognitive dysfunction starting when dogs are 10 or 11 years old, a trend that is unrelated to size.
“The pattern of cognitive decline as a function of age is the same, on average, for dogs of all sizes, suggesting that shorter lived large-breed dogs don’t show cognitive decline sooner,” Dr. Promislow says. “It’s like the age trajectory of cognitive decline is the same. We don’t see it much in large-breed dogs because most of them don’t live until an age where we begin to see cognitive decline.”
That unusual finding has led to one paper being published, with another in the works.
Cancer, too, is an important disease of aging. The DAP has received funding from the American Kennel Club’s Canine Health Foundation to support the study of lymphoma across breeds, with the hope of understanding why some breeds are at greater risk than others. They’re also studying links between cancer and aging.
There’s no magic pill to keep pets young. Yet. For now, the secret to keeping aging pets healthy is the same as it is for aging humans: eat right, exercise, and see the doctor on a regular basis.
Part of eating right is keeping weight off to prevent painful pressure on deteriorating joints. Measuring food instead of free feeding is one way to help keep them from putting on the pounds. And it’s a common misconception that protein is bad for kidneys. Senior animals need foods with high-quality protein that’s easily digestible.
Dogs may benefit from foods with ingredients to boost brain health. Studies have shown that foods supplemented with medium-chain triglycerides from coconut oil as well as nutrient blends containing fish oil, B vitamins, antioxidants, and arginine can aid memory, social interaction and learning ability in dogs.
Brain-teaser games help, too. Food puzzles that require pets to manipulate them to get food or treats to fall out are good mental and physical stimulation.
Dogs will still enjoy walks and other activities appropriate for their physical state. Agility, chasing a ball across a park, or leaping to catch a flying disc are all high-impact activities. If your dog seems to tire more quickly or shows signs of arthritis, it may be time to switch to low-impact play such as nosework, rally, or swimming.
Watch for signs such as whether your dog is tired in a good way after an activity or seems wiped out. How they act the next day is important too. Perky, eating well, and interactive is good; lethargic with little interest in food, not so much.
Oral health is important. Dogs whose mouths are painful from gum disease, broken teeth, or other dental problems often find it difficult to pick up and eat their food. They may start eating less or picking up food and dropping it. Keeping the mouth pain-free as dogs age is key to their wellbeing.
As pets enter the golden years, it’s a good idea to start scheduling twice-yearly veterinary visits. Animals age more rapidly than humans, and for senior animals a lot can change in six months.
“A good way to practice preventive medicine in our seniors is to have routine lab work run,” says Harmony Peraza, a veterinary technician and study subject manager for the Dog Aging Project at Texas A&M College of Veterinary Medicine and Biomedical Science. The regular checkups can help catch diseases before they progress and become difficult to treat.
Will your pupper one day be treated by a veterinary gerontologist—a specialist in pet aging? Gerontology isn’t a recognized specialty yet but it wouldn’t be surprising if some future veterinarians follow that route. Most of us consider pets full-fledged members of the family, and there has been a corresponding increase in the willingness of pet parents to provide extensive veterinary care for animals as they age.
“With the increasing use of human medical procedures and drugs in older dogs, it makes perfect sense that you’re going to want to have people who specialize in that,” Kaeberlein says. “So I expect that will happen. And studies like ours that are going to be collecting a lot of data on dogs as they go through the aging process can contribute to that.”
There’s currently no way to turn back the pet aging clock, but scientists are working on making a longer healthspan—the amount of time dogs stay healthy—a possibility.
“I believe that within the next five to 10 years we will start to have some medications that are clinically demonstrated to modulate the aging process, delay age-related diseases, and hopefully extend healthy lifespan in pets,” Kaeberlein says. “I feel like we’re on the cusp now. We know of several drugs that seem to slow the aging process in laboratory animals, in mice in particular, some quite significantly. I expect that we will start to gain some evidence that some of these medications work the same way in dogs.”
Researchers with the Dog Aging Project are currently tracking 32,000 dogs in homes around the United States to study how genetic and environmental factors affect canine aging. They hope that the long-term observational study, which includes all kinds of dogs in all kinds of households—short-lived dogs, long-lived dogs, dogs of all sizes, breeds, and mixes, and dogs at all economic strata—will eventually have 100,000 dogs enrolled.
Researchers will look at how long the dogs live as well as how environmental factors affect them as they age. Dr. Promislow describes it as “the science of paying attention, of watching closely what happens over the years.”
Because dogs’ lives are shorter, the researchers can see more quickly how they may be affected by environmental factors such as pollution or lead content in paint or other elements that affect humans as well. Rather than looking at humans for 30 or 40 years, over a shorter period, Promislow says, “we can learn how those environmental risk factors or beneficial environmental factors impact dogs.” What they learn will likely benefit both humans and dogs. “I think there will be in the coming years many lessons that we learn that are very relevant for people,” Promislow says.
Approximately 500 medium-size to large dogs will participate in a one-year intervention study, receiving low doses of a drug called rapamycin that in laboratory and some human studies appears to slow or improve healthy aging. The double-blind placebo-controlled study means that neither owners nor researchers will know which dogs receive the drug and which receive a placebo. The primary goal is to see if treatment with rapamycin helps dogs live longer lives. The study will also ask if treatment with rapamycin improves heart function as middle-aged dogs get older.
And there’s much more to learn. In humans, for instance, loss of the sense of smell is predictive of cognitive dysfunction and it would be interesting to test if this is true in dogs as well. So far, however, there’s not yet a good way to measure reduced sense of smell in dogs and whether it may be related to cognitive decline, but Promislow thinks it’s an important avenue of study.
The DAP is just at the beginning of starting to turn data into science.
“We’re already seeing some cool things, like this surprising observation that short-lived dogs don’t show early cognitive decline relative to long-lived dogs, suggesting that there’s something that’s protecting cognitive function that doesn’t protect physical function in the same way,” Promislow says. “That’s surprising and really interesting and opens up a whole set of questions to try and understand why.”
The Dog Aging Project: https://dogagingproject.org/
NHGRI Dog Genome Project: https://research.nhgri.nih.gov/dog_genome/
Canine Longevity Study of Two “Methuselah” Dogs: https://www.frontiersin.org/articles/10.3389/fgene.2020.00315/full
Study comparing dog and human aging: https://www.nih.gov/news-events/news-releases/nih-researchers-reframe-dog-human-aging-comparisons
Age influences domestic dog cognitive performance independent of average breed lifespan, published online in the journal Animal Cognition, April 30, 2020. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7384235/
Dog years vs. human years: https://www.science.org/content/article/here-s-better-way-convert-dog-years-human-years-scientists-say
Questions to Ask Your Veterinarian
Is my breed or mix at risk for certain diseases? Which ones and what preventive steps can I take?
Is it true that dogs age seven years for every human year?
Does my senior dog need a special diet?