How Your Dog Is Likely to Age Based on Size, Head Shape

Smaller dogs can live up to twice as long as their larger counterparts, research from Eötvös Loránd University in Hungary shows. And yet, this longevity is accompanied by an increased rate of canine cognitive dysfunction.

Based on data from 15,000 dogs, the team, led by Borbála Turcsán, the team investigated the age at which behavioral and cognitive changes begin to show and how fast they progress in different dog breeds.

"The inverse body size/lifespan relationship within species is a well-known phenomenon in biology," Turcsán told Newsweek. "Although the exact physiological mechanisms underlying this trade-off in dogs is still unknown, research on other species, as well as some theoretical models on mortality data, suggest that it has to do with growth rates/aging rates. That is, larger individuals have higher growth rates, which can result in higher rates of cellular damage during early life, potentially having long-term negative effects on the animals' health maintenance and longevity."

However, what they did not know was whether larger dogs also had shorter healthspans than their smaller counterparts. In this study, which was published in the journal GeroScience on September 23, they found that, while dogs weighing more than 66 pounds show an earlier onset of age-related decline—by about two or three years—the rate of this decline was slower compared with smaller dogs.

"We found that there is a trade-off between longevity and relative healthspan which concerns mostly the two extreme sizes," Turcsán said. "Small [toy] dogs have a much higher expected lifespan, but they also have a much higher risk of developing mental health problems.

"Large [giant] dogs have a shorter expected lifespan, but it is accompanied by a relatively long mental healthspan and a lower prevalence of canine cognitive dysfunction[...]we found that the smallest size group showed more than 4 times higher prevalence of canine cognitive dysfunction than the largest group."

Head shape also played a role, with long-nosed dogs twice as likely to experience cognitive dysfunction a medium- and short-nosed dogs.

"Even though short-nosed dogs have higher predisposition to various diseases which poses a severe welfare problem, in this particular case, long-nosed dogs are at higher risk," Turcsán said.

Perhaps unsurprisingly, pure breeds were also found to have higher frequencies of cognitive decline than mixed breeds.

"It seems that the genetic advantage of hybrid vigor of mixed breeds helps them maintain their cognitive health for longer periods," Turcsán said.

But what do these results mean for potential dog owners, deciding which breed they want to welcome into their family?

"For owners who want a smaller sized dog but do not want to risk severe mental health problems in old age or want a larger sized dog but do not want to risk physical health problems at 7 to 8 years of age, we recommend a dog from the 14 to 66 pounds size range," Turcsán said. "Based on our results, these dogs have a longer healthspan relative to their expected lifespan than both their smaller and larger counterparts."

Their results may also help inform future veterinary health programs, as well as improve our understanding of aging in our own species.

"Our results have significant translational implications for human aging research, but they also carry a practical significance for owners and veterinarians and lay the foundation for future research about the risk factors and prevention of age-related cognitive decline, that can help developing interventions to maintain the dogs' physical and mental well-being as they age," Turcsán said.