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    How old is your dog? Is the 7:1 ratio correct?

    NewsGeneral Dog NewsFriday 10 May 2013
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    As far as most of us are concerned, you simply work out your dog’s age by multiplying its age - in human years - by seven. However, it seems that this theory is based on nothing more than a school maths book. 

    No-one actually knows where this seven dog years to one human year theory came from and no-one is claiming to have come up with it. It is thought to have first appeared in maths text books in the 1960s when questions were set asking children to calculate the age of a dog using the 7:1 ratio. 
     
    Thought this theory offers you a fun way to work out your dog’s actual age, it is far from the truth. A number of dogs have been known to live over 20 years (human years), which would make them over 140-years-old. This proves that the theory is wrong as no human has ever been known to live beyond 122. 
     
    So, if seven dog years, to one human year is wrong, then how do we work out an accurate calculation? 
     
    Being the most diverse species on the planet, dogs can vary in weight from 6lb (3kg) to 200lb (90kg) when they are fully grown and they also have widely varying body shapes and hair types. This also means that they all have very differing life expectancies, meaning one rule for all dogs is very unrealistic. In fact, smaller dogs tend to live longer than their larger cousins. 
     
    Speaking to the BBC on the topic, Daniel Promislow, professor of genetics at the University of Georgia, said:  "If you think about statistical correlation between average life span and body size in mammals it generally tends to be positive - gorillas, elephants and whales are much longer lived than shrews, voles and mice.”
     
    Promislow has his own theory why this is and said: "The disease that shows the strongest correlation with size is cancer.
     
    "We know that cancer goes up even faster with age than mortality does. The rate of cancer increases very dramatically with age - the same as in humans."
     
    So it may be because the risk of cancer increases so much, and because large dogs are at such a higher risk of dying of cancer (roughly 50% chance), that large dogs generally have shorter lives than small dogs (roughly 10% chance of dying of cancer).
     
    And, just to over complicate things even more, this fact is true despite the fact that smaller dogs reach adulthood faster than big dogs. 
     
    "Small dogs reach skeletal and reproductive maturity sooner than larger breeds. Once they've achieved those measures of adulthood they carry on to live longer," says Dr Kate Creevy, assistant professor of internal medicine at the University of Georgia.
     
    So this basically means that smaller breeds have a shortened juvenile period and an extended adulthood. Large dogs, on the other hand, may take two years to get to their fully mature skeletal body size and then they may only live another four or five years.
     
    The Bulldog for example only lives on average until it's six years old whereas a Border Terrier lives on average to the age of 14.
     
    So, bizarrely, a small dog is older than a big dog at two human years - but younger at five.
     
    Kate Creevy continued: "It doesn't happen in any other animal. There isn't any other species which has within a single species the same degree of size diversity that dogs have. It's possible that by creating all of these diversely sized dogs that we unmasked this ageing phenomenon."
     
    So, the truth is no-one knows how to work out the age of a dog in human years, so if your dog is nearing 100, don’t panic, it doesn’t spell the end!
     
    We want to know how many people still use the 7:1 ratio, and if so, how old is your dog? Let us know in the comments below...
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