Cell studies suggest oxidative stress may doom Great Danes and other big dogs to shorter lives
NEW ORLEANS, LOUISIANA—For most mammals, size matters: Large ones, such as elephants and whales, live far longer than small ones like rodents. But among dogs, that rule is reversed. Tiny Chihuahuas, for example, can live up to 15 years—8 years longer than their much larger cousins, Great Danes. Now, a team of undergraduates may be closer to figuring out why. The most likely culprit? More harmful oxygen free radicals in fast-growing, fuel-burning puppies.
When an organism grows, its cells break down food to make the molecular fuel they need. But generating this energy can also generate an unwelcome visitor: renegade molecules called oxygen free radicals. These molecules are missing electrons, and as they try to poach them from other cells in the body, they can quickly damage cell membranes and eventually contribute to cancer and other diseases. Molecules known as antioxidants neutralize these free radicals. But ultimately, the more energy a body produces, the more free radicals it makes, and consequently, the more antioxidants it needs. Some scientists think that escaped free radicals contribute to aging, although this is hotly debated.
To find out whether that might be true in canines, undergraduates Josh Winward and Alex Ionescu from Colgate University in Hamilton, New York, asked veterinarians for the ear clips, dewclaws, and cut-off tails of puppies and the ear clips from old dogs that had recently died. Altogether, they collected about 80 samples from large and small breeds. Working with Colgate animal physiologist Ana Jimenez, the students isolated cells from those tissues, grew the cells in a lab dish for a few weeks, and then analyzed them.
In the adult dog cells, energy and free radical production was about equal in the two breed sizes. But in the puppy cells, that balance was off. Adult large and small dogs had about equal amounts of antioxidants, but the cells from large breed puppies had too many excess free radicals for the antioxidants to fight, the undergrads reported here last week at the annual meeting of the Society for Integrative and Comparative Biology. Thats likely because large breed puppies have fast metabolisms, growing faster and requiring more energy than smaller breeds, Winward says. Cell damage even at this young age can have long-lasting effects.
The results are preliminary, and there are other ideas about why dogs age the way they do. But if the findings hold up, it might be possible to extend large dogs lives with antioxidant supplements for puppies, Winward suggests. These antioxidants could help get rid of those young dogs extra free radicals before they do damage.
Adam Brasher, an undergrad studying the effects of oxygen free radicals at Auburn University in Alabama is cautious. Excessive amounts of these molecules can be detrimental, he concedes, “but moderate levels are beneficial.” To figure out what level of antioxidants are helpful, and whether their findings apply more broadly to other breeds, Jimenez and her students plan to expand the current study next summer. “Stay tuned!” she says.
Liz Pennisi is a senior correspondent covering many aspects of biology for Science.
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According to new research, it’s because they age faster. A study in the American Naturalist drew data from the Veterinary Medical DataBase that covered 74 breeds and over 50,000 dogs and looked at when and why they died. The American Society of Naturalists writes:
This sounds simple: big dogs age quicker than little dogs. But it’s still not clear why that’s true. Answering this question could actually teach researchers about genetics and physiology not just of dogs, but of humans too.
The average Great Dane spends about seven years on this earth, digging holes and smelling everything it can. The average teeny tiny Toy Poodle will double that lifespan, to 14 years or so. And that difference holds for most dogs—the bigger they are, the shorter their lives. This is kind of weird, because, when you compare size across species, it’s not necessarily true that bigger animals live shorter lives. Some very large animals live quite long lives. Elephants stick around for 70 years, and blue whales can live to 90. So why do bigger dogs die sooner?
Clubs Offering:
When it comes to the lifespan of dogs, researchers have found that size matters. Owners of small dogs can expect to enjoy several more years with their pets than the owners of large dogs.
It doesn’t seem to make much sense: large mammals, like elephants and whales, tend to live longer than small ones, like mice. So why, then, do small dogs have a longer average lifespan than larger breeds?
This phenomenon has baffled scientists for years, and although the reason why is still uncertain, there are several theories that researchers have explored. In addition to being important to the health of our canine companions, scientists hope this research will allow them to gain a better understanding of the human aging process because as dogs age, they experience many of the same conditions we have – such as arthritis, cancer, and diabetes.
It’s important to understand what it really means when we say how old our dogs are. Dogs and people age at very different rates. When dogs reach one year old, veterinarians estimate they have matured as much as people have when they reach 15 years old. The second year in a dog’s life equates to about another 9 years for a human. And after that, the aging process in dogs varies based on their age and size.
Although large mammals tend to live the longest, small body size within a species is associated with longer life and slower aging. Canis familiaris, aka the domestic dog, is a species with a huge size range when it comes to its breeds.
Cornelia Kraus, an evolutionary biologist at the University of Göttingen in Germany, was the lead researcher of a major study of 74 breeds and more than 56,000 dogs seen in North American veterinary teaching hospitals. Kraus reported that large dogs age at an accelerated pace, and “their lives seem to unwind in fast motion.”
In the study, large breeds died more often from cancer than small breeds. Why? One possibility Kraus suggests is that large breeds grow faster, so they may be more likely than small dogs to also experience the abnormal cell growth seen in cancer. Or because they age more quickly, large dogs may succumb to age-related illnesses sooner.
A researcher at the University of Washington, Dr. Silvan Urfer, conducted a large study, collecting data on 169,000 dogs who died or were euthanized within a three-year period at U.S. veterinary clinics. He found a correlation between the breed of the dogs and their age at death. For example, among giant breeds, Great Pyrenees lived longer (11.55 years) than Great Danes (9.63 years).
In Dr. Urfer’s study, small dogs had a longer median lifespan at 14.95 years, medium-size dogs lived an average of 13.86 years, and large dogs lived 13.38 years. The dog’s body size was the most important variable in predicting lifespan, more important than whether or not the dog was purebred.
Another factor researchers have studied is the size of the breeding population, and its impact on health and longevity. One study of companion dogs “did not find significant differences in lifespan between purebred and mixed breed dogs; however, breeds with larger effective population sizes and/or lower inbreeding coefficients had median survival times 3-6 months longer than breeds with smaller effective population sizes or higher inbreeding coefficients, indicating that these measures of genetic diversity may be affecting breed lifespans.”
In the Journal of the American Animal Hospital Association, Dr. Urfer reported when comparing two dogs with all other factors being equal, that he found annual dental cleanings conducted by a veterinarian reducing risk of death by almost 20 percent. Dr. Urfer pointed out that there could be a direct association between good dental health and good general health, but it might also be that dog owners who take good care of their dog’s teeth would also be more likely to provide preventive and veterinary care that contribute to longevity.
New research from the WALTHAM Centre for Pet Nutrition and the University of Liverpool revealed overweight and obese dogs are more likely to have shorter lives than those at ideal body weight. Study co-author and Professor of Small Animal Medicine at the University of Liverpool Alex German said, “Owners are often unaware that their dog is overweight, and many may not realize the impact that it can have on health. What they may not know is that, if their beloved pet is too heavy, they are more likely to suffer from other problems such as joint disease, breathing issues, and certain types of cancer, as well as having a poorer quality of life. These health and wellbeing issues can significantly impact how long they live.”
One study that focused on 12 specific breeds found the effect on lifespan of extra weight on the smallest dogs, such as Yorkshire Terriers, was even greater (overweight: 13.7 years, normal: 16.2 years) than the effect on larger dogs such as German Shepherd Dogs.
Another study asked a very interesting question about dog cognition. Since large dogs have a speedier growth rate and physiological pace of aging than small dogs, do they also have a faster pace of cognitive development? Researchers measured cognitive development and aging in more than 4,000 dogs from 66 breeds using nine memory and decision-making tasks. They found that all breeds, regardless of size or lifespan, tended to follow the same speed of cognitive aging, no matter the size of the dog.
These findings are just the tip of the iceberg in our understanding of canine lifespans and what determines them. A grant from the National Institute on Aging is funding a project, called the Dog Aging Project, to explore the biological and environmental determinants of aging in dogs.
The project is based at the University of Washington and Texas A&M College of Veterinary Medicine and Biomedical Sciences. Nearly 30,000 dogs and their owners from across the U.S. are participating. Scientists and research veterinarians from 20 research institutions and veterinary teaching hospitals are following the health and aging process of these dogs for 10 years or more to understand how genes, lifestyle, and environment influence aging.
According to the project website, “This information will be used to gain insights that will increase our ability to prevent, diagnose, and treat age-related diseases, thereby helping our dogs, and by extension, ourselves, live longer, healthier lives.”
Dog Years: Why Do Small Dogs Live Longer Lives than Larger Breeds – Animal Facts
(ISNS) — Most large dog owners know they are setting themselves up for heartache because their beloved pets will die much sooner than smaller breeds.
The correlation between size and lifespan in dogs is well documented, but scientists are still unclear about the reasons behind it. Why, for example, does a 150-pound Great Dane only live for about 7 years, while the average lifespan of a 9-pound toy poodle is 14 years?
“This tradeoff has been known about for a long time, but nobody has yet investigated the underlying demographic mechanism,” said Cornelia Kraus, an evolutionary biologist at the University of Göttingen in Germany.
For example, veterinarians recommend starting geriatric checkups for small dogs around age 11, for medium-sized dogs at around age 9, and for large dogs around age 7.
One might assume from this that large dogs age faster, Kraus said, but it could also be that they just started aging earlier, and thus develop age-related problems sooner.
In order to distinguish between these two hypotheses, Kraus and her team analyzed demographic data, including age and cause of death, for more than 50,000 dogs from 74 breeds taken from the Veterinary Medical Database, a compilation of pet-health data from North American veterinary teaching hospitals.
The researchers also considered a third possibility: large dogs may just have an increased mortality risk throughout their lives, regardless of their age. In other words, their “baseline” mortality rate is higher than that of smaller breeds.
Each of these three hypotheses generate different so-called “mortality curves” — a chart that results when mortality risk is plotted against age on a graph.
When the different dog breed data from the database was graphed, its curve most closely matched the one predicted by the faster-aging hypothesis.
The analysis also indicates that large dogs age at an accelerated pace, such that “their adult life unwinds in fast motion,” the authors write in a new study that will be published in an upcoming issue of the journal The American Naturalist.
The new findings are a valuable first step toward answering the question of why large dogs die young, said Cynthia Kenyon, an aging researcher at the University of California, San Francisco.
“I think whats really nice about this study is that these are not lab animals,” said Kenyon, who was not involved in the research. “Theyre animals living out their lives in the real world.”
Future studies might also investigate why larger dogs age faster, something that the current study doesnt address, Kenyon added. One intriguing clue, gleaned from previous studies, is that small dogs have lower concentrations of the growth hormone IGF-1, or insulin-like growth factor 1, in their blood than large dogs.
High levels of IGF-1 has been shown in a wide variety of organisms, including humans, to be associated with increased risk of death from age-related diseases such as cancer and heart disease. Conversely, manipulations that lower IGF-1 levels in many animal species slow their rates of aging, reduce the risks of age-related disease and extend their lifespans.
The new findings “might give the sense that the reason large dogs age faster is because they grow faster. But we dont know that,” Kenyon said.
It could be that large dog breeds die younger because they have more IGF-1 – their large size might just be a side effect of having higher concentrations of the growth hormone.
One way to test this hypothesis would be to “take a small dog, and give it high levels of IGF-1 when its young so it becomes a large dog,” Kenyon said. “Then, when its an adult, go back to a lower level [of the hormone], and see if you still get a long lifespan. I think that would be a very interesting experiment to do, but it has not been done.” Such an experiment could provide further proof that IGF-1 plays a critical role in the aging process. Furthermore, the fact that small dogs – which naturally have lower levels of IGF-1 – are often healthy throughout most of their lives could suggest that the IGF-1 pathway could be manipulated to make organisms live longer.
“This really argues that perturbations in this pathway that increase lifespan wouldnt necessarily make you sick in any way or have a detrimental effect on your health,” Kenyon said.
There is some circumstantial evidence that taller individuals have shorter lifespans, Kraus said, but “it is incredibly difficult to study this in humans because we have so many environmental factors that affect our height.”