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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鈥檛 seem to make much sense: 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 鈥� such as arthritis, cancer, and diabetes.

Human Vs. Dog Years

It鈥檚 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鈥檚 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.

Size Matters

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 G枚ttingen in Germany, was the lead researcher of a 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 鈥渢heir lives seem to unwind in fast motion.鈥�

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, , 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鈥檚 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鈥檚 body size was the most important variable in predicting lifespan, more important than whether or not the dog was purebred.

Breeding

Another factor researchers have studied is the size of the breeding population, and its impact on health and longevity. One of companion dogs 鈥渄id 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.鈥�

Dental Health

In the , 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鈥檚 teeth would also be more likely to provide preventive and veterinary care that contribute to longevity.

Weight

from the WALTHAM Centre for Pet Nutrition聽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, 鈥淥wners 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.鈥�

One 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.

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Cognitive Development

Another study asked a very interesting question about . 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.

The Search Goes On

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 , 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, 鈥淭his 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.鈥�

How Can I Make My Dog Live longer?

Thanks to advances in veterinary science and preventive medicine, the life expectancy of our dogs is increasing. We can help our dogs live longer higher quality lives by:

• Feeding a healthy diet
• Helping maintain a healthy weight.
• Encouraging breed- and age-appropriate physical and mental exercise.
• Taking our dogs for annual veterinary checkups and vaccinations.
• Providing preventive dental care.
• Administering heartworm, flea and tick preventatives.
• Keeping them safe from accidents.
• Providing love and affection.