Monday, January 11, 2010

How dogs can withstand the cold better than humans

It would seem that dogs must be somehow physically different from humans. I have watched them romp and play in the snow, and even walk about on ice, their feet in constant contact with the elements, yet they have no problems and continue on as if it were nothing. Yet I, even with gloves and boots, still manage to think I’m about to lose my fingers and toes due to frostbite. Dogs have two distinct advantages over humans in keeping their extremities going in colder temperatures.


The first physical difference
The first physical difference is in how their blood vessels are arranged at their extremities. As humans our bodies are designed to restrict the blood flow to the extremities if they are exposed to very cold temperatures. It’s a survival mechanism, we can live without fingers or toes, but if our core temperature drops to a certain level, we die. Imagine not wearing gloves, and the warm blood that enters your fingertips loses that heat at the tips, and then returns to the heart much colder then when it left. The body recognizes this as a potential lethal problem, and constricts the flow of blood to those fingertips in a effort to reduce the heat lose to the core.

Dogs limbs however are a bit different. The vessels that carry the blood from the heart to the pads, literally lie right up against the return vessels. The warm blood flowing out the tips literally is able to transfer some of the heat to the colder blood returning to the heart, in effect warming it up before it reaches the core. The core temperature therefore drops much slower and the dog’s body is much less inclined to restrict the blood flow to the extremities. It’s almost as if the blood is playing a trick on the body in order to keep the extremities alive longer, which seems as if it would become even more dangerous eventually. This leads us to the second physical difference. NOTE (This may in fact have something to do with why they pant in the summer as an alternative air-conditioning, since their skin at the extremities is not as well designed to conduct heat to the environment.)

The second physical difference
The second physical difference in dogs is in the actual flesh of their lower legs. If our blood played the above trick on us we would likely lose a lot more than just our fingertips to the frostbite, our entire hand might become entirely frostbitten at the same time. The flesh in our bodies contain a good deal of fat. Consider tallow. Tallow is a form of rendered fat that comes from animals and is pretty solid at room temperatures, resembling the white solid vegetable shortening you might use for cooking. Now consider Neatsfoot oil. Neatsfoot oil is also a form of rendered fat that also comes from animals, and is in a completely liquid state at room temperature.

Here’s the most interesting part. Tallow is derived from the core area of animals, while Neatsfoot oil is derived from the extremities. You see, nature has designed animals so their feet do not freeze solid as quickly as the rest of them might if it were constantly in contact with the snow and ice.  So the combination of tightly packed blood vessels and fat tissue that doesn't turn solid as easily allows dogs to expose their feet to the cold much longer than us humans could ever dream.  Pretty cool!

Read my blog about dogs and cold weather

A more detailed article on these physical traits

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