How Our Pets Age, And What They Can Tell Us About Human Ageing

Anyone who has owned a pet will know that just like humans, companion animals seem to go through stages in their life as they age. Many parallels can be drawn between humans and pets when it comes to the physical and behavioural changes that occur with ageing. Elderly dogs might not be so enthusiastic about their walk as they once were. On the other hand, some of these changes are positive – anyone who has experienced the destructive tendencies of a young cat or dog can attest to that.

How do these anecdotal observations stand up to science? Do our pets age in the same ways as us, and can we really draw parallels between phases of human and animal lives? Do pets go through adolescence?

According to the science so far, the answer appears to be yes: broadly speaking, pets undergo similar physical and behavioural changes to humans as they age. For example, one study found that border collies seem to ‘mellow’ with age. There is also evidence that adolescent dogs are less willing to obey commands – make of that what you will!

Importantly, cats and dogs also undergo similar age-related changes to their DNA. DNA methylation is a process that alters the activity of different genes, and occurs in a predictable way throughout life. To assess the true biological age of an organism, scientists can use a methylation clock – a technique to calculate how far ageing has progressed based methylation patterns in the DNA.

The development of DNA methylation clocks for both dogs and cats not only helps us to understand how our pets age, but also to translate this understanding to humans. For example, we now understand that one ‘dog year’ is not equivalent to seven ‘human years’. According to one study, you can estimate how old a Labrador retriever is in human years by taking the natural log of the dog’s age, multiplying by 16, then adding 31. In simple terms, this means that dogs seem to age much more rapidly than humans in early life (about 30 human years in one dog year) before slowing down in later life.

Methylation clocks have also been developed for cats, and while a comparison like the one above doesn’t appear to have been made in cats yet, it is plausible that the situation in felines should be similar, given the rate at which kittens mature.

This research could have implications for the study of ageing in humans. In particular, it has been argued that dogs could serve as good model organisms for the study of ageing. The reasons for this are, in essence:

• Dogs suffer from many of the same age-related diseases as humans (obesity, arthritis, hypothyroidism, diabetes…)
• Dogs age much faster than humans, making it far more practical to study dog ageing throughout life.
• There is a large population of pet dogs that could be recruited into any scientific study, and those dogs share the same environments as their human owners.
• Much like humans, some dogs are outliers that have exceptionally long lifespans, and understanding what makes these dogs different could help us understand how to slow the ageing process.