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why do small dogs live longer

Why Do Small Dogs Live Longer?

Have you ever wondered why small dogs live longer? Although still a debated topic, new research suggests life expectancy is determined during the early stages of development.

Smaller dog breeds outliving larger breeds seems to go against the rest of the mammalian kingdom. For example, mice live for only a few years whereas elephants can live for up to 70 years! Comparing this to dog breeds, a jack russell will live for around 15 years, whereas the great dane has a life expectancy of 6-7 years.

Undergraduates Josh Winward and Alex Ionescu from Colgate University, New York investigated the possible reasons why this rule is reversed in dogs.

A Link Between Free Radicals and Life Expectancy?

When mammals produce energy from food, free radicals are produced as a by-product. Also known as reactive oxygen species (ROS), these molecules are destructive and cause damage to cells. ROS have an unpaired electron and will strip electrons from other molecules in the body to stabilise themselves. This process causes damage to cell membranes and can contribute to diseases and cancers.

Fortunately, the body has a defence mechanism- antioxidants. Antioxidants roam the body, stopping free radicals from damaging cells. Vitamin E and vitamin C are good examples of antioxidants.

Large breed puppies grow much faster than their small breed counterparts. As a result, they have a faster metabolism and need more energy to reach their adult size. This increased energy demand also produces more free radicals.

In human medicine, free radicals have been linked to ageing. The free-radical theory of ageing suggests organisms age because of damage done to cells by ROS over time. The study authors investigated whether this could be why small dogs live longer.

Investigating Why Small Dogs Live Longer

Winward and Ionescu took tissue samples from various puppy breeds as well as older dogs that had recently passed. With these samples, they were able to determine the free radical and antioxidant content of cells.

In the cells of adult dogs, free radical production was proportional between small and large breeds. When looking at the samples from puppies, free radical production in larger breeds was not balanced by antioxidants 1.

A large influx of free radicals can damage DNA through cross-linking. In turn, DNA cross-linking can cause various effects of ageing including disease and cancer 2.

At adulthood, the free radical levels are balanced in both small and large breed dogs. However, it seems that damage done by excessive free radical production at a young age can have long lasting effects. By this theory, small dogs live longer because less damage is caused by free radicals during their development as a puppy. 

Small dogs live longer because less damage is done by free radicals during puppy development Click To Tweet

Could Antioxidants Slow Down Ageing?

This claim is one often seen in human medicine and we are regularly reminded of the benefits of antioxidant-rich foods such as blueberries. But are antioxidants going to help your Irish wolfhound live till 14? Colgate animal physiologist Ana Jimenez and her students intend to carry on the work in this study to find out what level of antioxidants are beneficial.

Numerous studies ‘tentatively’ support the current free radical theory of ageing, but it is still evolving and not conclusive.

One series of study found that senior dogs fed an antioxidant rich diet performed better at complex tasks than dogs fed a control diet 3. This correlates with the free radical theory of ageing that ROS damage contributes to brain ageing. In dogs this condition is known as canine cognitive dysfunction (CCD). Try our calculator to see if your dog may have CCD symptoms.

Given the number of studies that provide even tentative support for antioxidant use, adding them to your pet’s diet is worth the investment. Key life stages such as during puppy development and senior years would be the best time for antioxidant intervention.

If you’re looking to boost your dog’s antioxidant intake, you can use antioxidant supplements, or look for dog foods rich in antioxidant ingredients such as vitamin E, vitamin C, selenium and beta-carotene.

Featured Image – Boxer mix puppies, bullcitydogs


References:

  1. Why large dogs live fast—and die young | Science | AAAS, doi: 10.1126/science.aal0608
  2. Dizdaroglu, M. and Jaruga, P. (2012). Mechanisms of free radical-induced damage to DNA. Free Radical Research, 46(4), pp.382-419.
  3. COTMAN, C., HEAD, E., MUGGENBURG, B., ZICKER, S. and MILGRAM, N. (2002). Brain aging in the canine: a diet enriched in antioxidants reduces cognitive dysfunction. Neurobiology of Aging, 23(5), pp.809-818.

About James Watts

BSc Bioveterinary Science. Editor of PetSci. When I'm not writing, learning, discussing, or reading about animals, you know it's the weekend! Currently developing PetSci HealthTrak, the fast and easy way to monitor your pet's weight and calorie intake. HealthTrak offers a simple way to track your pet's progress, helping them achieve a healthy weight and a long, happy life.

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One comment

  1. Lynne Masters-Lee

    Commercial dog puppy food is high in things like calcium to build bones. Owners of giant breeds (Irish wolfhounds and Great Danes, primarily, are told to switch to adult food by the time they are three or four months old because the calcium level is too high for a dog that grows from under 7 pounds to over 100 pounds in a year’s time. Maybe the antioxidants will help, but in order to test that the researchers will have to work with breeders who will prepare an appropriate diet, as it can’t b e found in the market.

    Additionally, giants of all species have a shortened lifespan compared with what is considered normal size. Many extra tall and extra large humans also tend to have a shorter lifespan than their normal-sized family members.

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