June 14, 2024, 2:10 pm | Read time: 5 minutes

Small dogs generally live longer than their larger counterparts. But it’s not just size that influences the lifespan of our four-legged friends. A large-scale study revealed various factors that influence the lives of these animals and identifies the dogs that stay healthy the longest.

The study investigated the relationship between the size of the animal, their head shape, their aging processes and their breed. Specifically, the researchers were interested in the following questions:

• How fast is the aging process in different breeds?
• When do the first signs of canine cognitive degeneration, i.e., the equivalent of dementia, appear in dogs?
• How do dogs’ expected lifespan, body size, breed, or head shape affect their health and life expectancy?
• When does cognitive performance begin to decline, and how quickly do different dogs get weaker after showing the first signs?

Data from 17,000 cases should reveal everything about a dog’s lifespan and health

Over nearly four years, scientists gathered data from 17,428 dogs across 57 different countries, with 59 percent being pedigree dogs and 40 percent mixed breeds. Almost one percent did not specify their breed.

The researchers also sought to determine when dog owners themselves perceive their pets as old. This reluctance often stems from owners’ difficulty acknowledging their pets’ aging. As a result, dogs are sometimes only treated for age-related diseases once they have already begun to have a negative impact on them.

Additionally, the scientists analyzed whether the distinct head shape of brachycephalic breeds, like pugs or French bulldogs, correlates with statistically significant health predispositions.

Also interesting: Why pugs should be banned in Germany

The influence of various factors on a dog’s lifespan

Leveraging the extensive dataset, the researchers demonstrated that small dogs can live more than twice as long as their larger counterparts. Large dogs also show the first signs of cognitive decline at the age of seven or eight. This mainly affects dogs over 30 kilograms in body weight. In smaller dogs, the first signs of canine cognitive dysfunction only appear on average at 10 to 11 years of age. However, it has also been shown that, across a dog’s lifespan, this process progresses slower in larger compared to smaller dogs.

“Our study has shown that life expectancy, body size and head shape are associated with patterns of behavioral and cognitive aging,” the authors explain. However, only body size had a systematic influence on the aging trajectories of all the behavioral variables studied.

The findings also indicated that dogs weighing between 6.5 and 30 kilograms tended to maintain their health for longer relative to their life expectancy compared to smaller and larger breeds. In addition to size, the authors also linked head shape and breed status to the risk of dementia. Long-headed and purebred dogs are generally more susceptible. However, this is likely because brachycephalic and purebred dogs are more susceptible to breed-specific diseases than to typical signs of aging.

The largest and smallest dogs have the most problems

Consequently, a latent health burden was found in dogs of extreme size. This applies to very small, but also particularly large dog breeds. In animals weighing more than 30 kg, the decline in all behavioral variables examined began earlier, but then slowed down. Although the age-related changes were less marked compared to those in smaller groups, physical symptoms were still apparent. Toy or dwarf-sized dogs, on the other hand, live a long life but, according to the study, have a much greater risk of age-related mental decline.

“Larger dogs break down earlier physically, and the accumulation of diseases and the deterioration of sensory functions lead to ‘aging behaviors’ long before their mental decline sets in.” First-time author Borbála Turcsán explains these results further in a press release.

In the other groups, however, the results were not entirely clear in terms of life expectancy and head shape. According to the data, short-headed dogs had an earlier onset of cognitive decline and a slower rate of decline in brain performance, but only in certain behaviors such as training focus or “will to please”. Dogs with longer heads showed signs of aging more frequently, with short-headed dogs often suffering from breed-related diseases. This tendency was also evident in purebred dogs, which were more likely to suffer from breed-related diseases, but also showed a tendency towards cognitive decline. Consequently, the risk of dementia was lower in mixed-breed dogs.

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Owners considered their animals to be “old” far too early

One of the most interesting findings of the study was that owners considered their dogs to be “old” at the age of six, regardless of the dog’s size or breed status. This was four to five years earlier than the behavioral data would suggest. “This may be due to graying and barely noticeable changes,” explained study author Enikő Kubinyi, head of the Senior Family Dog Project, in a press release.

Thus, larger dogs maintain good mental health but experience physical decline at a young age, leading to premature death. But which dogs are the healthiest? “There is […] a trade-off between longevity and relative health span, but it seems to mainly affect the two extreme sizes. For dogs weighing between 6.5 and 30 kg, we found no differences in the aging process,” the study explains.

The authors therefore recommend a medium-sized dog for those who would like a smaller dog, without the risk of serious problems caused by age-related diseases. Even for those desiring a larger dog but wishing to avoid significant physical health issues, this size range is recommended.

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