Scientists have always conjectured that life span was related to resting metabolic rate and small animals like mice tend to have higher metabolism and shorter lives. Large animals, like whales, have a lower resting metabolic rate and based on this theory would be expected to live longer. Some of the ideas include that the faster rate of metabolism produces more oxygen free radicals that can age and damage tissues.
But dog lovers know that small breed dogs seem to outlive large breed dogs. Yorkshire Terriers routinely see ages of 15+, whereas Great Danes are considered elderly at 10 years. Dogs seem to defy the resting metabolic rate theories because small dogs have a greater metabolic rate which, in past theory, has been linked to shorter life span.
Recent studies have looked at this phenomenon and suggests that small dogs function at a lower ambient body temperature. This factor may affect the way in which the animal functions metabolically (at a subcellular level). This study found that animals functioning at a lower body temperature overall must rely on thermoregulatory mechanisms that seem to “flip the switch” on the metabolic rate theories producing fewer oxygen free radicals and positively affect longevity. ¹
Aging and longevity cannot be summed up in a single sentence or even a single theory. There is no escaping that we (and our dogs) are defined by our DNA also and studies have looked at the length and characteristics of the DNA in several breeds of dog. There are correlations between the biology of the DNA and life expectancy as well. ²
Genetics, of course, play a role in aging and disease and it isn’t reasonable to try to cool down your Great Dane, but it is interesting to know that size does matter, but not for the reasons we have always thought!
- J Exp Biol.2005 May;208(Pt 9):1717-30. Body size, energy metabolism and lifespan. Speakman JR.
- Cell Rep.2012 Dec 27;2(6):1530-6. doi: 10.1016/j.celrep.2012.11.021.Telomere length correlates with life span of dog Fick LJ Fick GH, Li Z, Cao E, Bao B, Heffelfinger D, Parker HG, Ostrander EA, Riabowol K
