Size and Lifespan

Dogs come in all shapes and sizes; little, big, cute, homely, hairy, and even hairless. Sure, other animals have this discrepancy in size between breeds as well, but not to the same extent as dogs. Take the cat for example; there are larger and smaller breeds but definitely not comparable to the Chihuahua and Great Dane in dogs. The Chihuahua weighs an average of 2-12 pounds with a life expectancy of greater than 15 years. Quite to the contrast, the Great Dane weighs in at a minimum of 120 pounds with an average life span of 8-10 years. Is this purely because of the difference in size, or are other factors involved?

Before we specifically answer this question regarding the relevance of size and lifespan in dogs, we must first look at all animals. Think of smaller animals: the mouse, hamster, insects; they all have a short lifespan. Now, consider what they do all day. These small animals are constantly running around, expending a lot of energy and having a high metabolism. Compare these small animals to larger animals: the elephant, tortoise, or whales; they all have long lifespans. What do they do all day? They do relatively the same things as the small animals. However, they are more efficient at utilizing energy because they are bigger and thus have a slower metabolism. Generally, the larger the animal, the slower their metabolism, and thus, the longer they live. This may just be due to the fact that they are not working as hard and so do not tire out as quickly. This theory sticks for most animals, but why then is it not true for dogs?

Metabolism rate does not seem to determine lifespan in dogs like it does for other species. Smaller dogs tend to live longer than larger dogs – the exact opposite of what you would expect! It is not exactly known why but may have something to do with the oxygen a body takes in every time it breathes. The body’s cells are efficient at using the oxygen to produce energy, however, sometimes “bad” by-products are made. It seems that fewer “bad” by products are made when the metabolism is higher. This may partially explain why small dogs may live longer than large dogs, but confuses the issue with all other animals if only this one theory is used.

Additionally, there are endless environmental circumstances and health issues that further complicate the lifespan of any animal. In fact, there are so many different complicating factors that the answer to why small dogs live longer than large dogs is still being researched. Is it possible dogs may actually not be the opposite to other animals in the large versus small lifespan? Perhaps large dogs would live longer than small dogs, but something gets in the way that prevents them from doing so.

Unlike most other animals, the dog was bred extensively through human intervention and selective breeding to make them exceedingly large, and also small. It is likely that some of these dogs became so large that their organs can just not adapt to having such a large body to take care of! Remember back to that tiny Chihuahua weighing a measly 2 pounds, overshadowed by the huge 120 pound Great Dane? The Great Dane is 60 times heavier than the Chihuahua, but certainly its internal organs, such as the heart, are NOT 60 times larger than that of the Chihuahua. The large dog’s organs have to work harder, and although they have a slower resting metabolism rate, this does the large dog no favours. Over the years the organs become weaker until they are overworked and no longer able to function. Switching back over to the smaller dog, could it be possible that they just live longer because the perfect size has been found that allows the body to function optimally for the longest period of time? Certainly this is possible. But remember, smaller isn’t always necessarily better – there is a myriad of health problems that afflict certain breeds of dog, and the smallest of the small are not always the healthiest individuals to begin with.

Has this article left you second guessing about getting a large dog because you want your companion living with you for as long as possible? It’s best to just store this information in the back of your head. Though interesting, you should not get a particular dog just because you think it will live long – any dog can come down with sudden illnesses and life-threatening problems. Choose a dog that best suits your lifestyle and you will cherish however many years you have with your pet.

By Laura Platt – Pets.ca writer