Categories: age related

The idea that a dog or cat year is equivalent to seven human ones is flawed

You might know this. The classic way of working out the human equivalent age of cats and dogs used to be to multiply their age by seven. That method is too crude by modern standards. It is far better to bracket the various ages of felines and canines and work out the human equivalent by reference to those groupings. The chart below shows this.

Young and old cat. Photo in public domain.

Cat to human years

Research on labrador helps

I was prompted to reassess the human equivalent ages of our pets after reading an article in The Times newspaper of Saturday, November 23, 2019. It’s about dogs but it is instructional if you want to work out equivalent cat ages and learn about the ageing process of pets.

The research has been published online on the website biorxiv.org. Researchers referred to the very popular labrador which they say grows up very fast with dogs of this breed reaching middle age in just two years. In short, this dog breed hurtles into middle age. At two years of age they have “puppy-like playfulness” but their DNA indicates that they are somewhere equivalent to the human age of the early 40s.

This seems to be an early spurt of ageing with the dog breed reaching the human equivalent of 50 at about their third birthday. Thereafter the rate of ageing slows so that a 10-year-old labrador is about the same age as a 68-year-old person.

The research refers to the process of ‘methylation’. For humans it happens at a relatively stable rate and as expected it is affected by lifestyle and health. This process allows scientists to estimate the age of the person. They do it by examining the methyl groups attached to their DNA. It is called the “epigenetic clock“.

The same process occurs in dogs and I must presume therefore in cats. Researchers at the University of California, San Diego looked at the rate of methylation in more than a hundred labradors. They compared dogs’ DNA methylation with that of humans aged from 1 to 103.

The scientists discovered that young dogs look like young people and old dogs resembled old people but after the infant stage dogs’ epigenetic clock speeds up. Mathematically they worked out a new method – what appears to be a very accurate method – of working out equivalent human age. You multiply the natural logarithm of a labrador’s age by 16, then add 31 to work out its equivalent age in human years. I don’t think you’ll be doing that 🙂 .

The concept of faster maturation was the same for all dog breeds. Although smaller dogs mature faster and tend to live for longer (chihuahuas live to about 20) while large dogs have an average lifespan of about 8 to 10 years.

People are not sure where the 1 to 7 year formula came from but it is flawed. They believe that it might have been started by veterinarians in order to get clients into their clinic for annual checkups. Sounds plausible….. 🙂

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Michael Broad

Hi, I am 70-years-of-age at 2019. For 14 years before I retired at 57, I worked as a solicitor in general law specialising in family law. Before that I worked in a number of different jobs including professional photography. I have a longstanding girlfriend, Michelle. We like to walk in Richmond Park which is near my home because I love nature and the landscape (as well as cats and all animals).

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