Post date: Feb 26, 2012 3:8:44 PM
DENVER, COLORADO, UNITED STATES (NBC) - Unlike humans, dogs have no problem going barefoot in the snow. Freezing temperatures appear to have no affect. Dog mushers in the frozen north of Alaska have exploited the animals' ability for more than a hundred years but it's only now that scientists are able to explain how the dog protects its paws. Professor Hiroyoshi Ninomiya of Yamazaki Gakuen University says dogs have an internal central heating system.
A scientist in Japan has come up with an explanation for how dogs can walk through the snow apparently oblivious to the freezing temperatures under their feet. Whereas humans have to wear shoes in the snow, dogs are specially equipped to deal with the cold.
"Dogs can walk in the winter on ice without any problem, because the back of their paw isn't made into a system that can actually get cold, there's that sort of mechanism at work," Ninomiya said.
The secret, says Ninomiya, lies in the method by which dogs circulate their blood to prevent cold surfaces from chilling the rest of their bodies.
"Dogs exchange heat at the end of their legs, arterial blood flows to the end of their legs and then heats up venous blood before returning it to the the heart. In other word, they have a heat exchange system in their feet," Ninomiya explained.
The system uses warm, oxygenated blood to heat the cold blood that has been in contact with cold surface before returning it to the dog's heart and central circulation.
By studying studying a preserved dog's leg under an electron microscope, Ninomiya found that because of the proximity of arteries and veins in the foot pad, the heat in the blood carried from the heart by the arteries is easily conducted to the cooler blood in the veins. This heat transferrence maintains a constant temperature in the foot pad, even when it has been exposed to extremely cold conditions.
Ninomiya says the mechanism for retaining heat is not limited to dogs, with many other animals such as seals and dolphins having similiar heat exchange systems. However, with dog breeders refining specific animals to cope with different conditrions, Ninomiya says that not all dogs may tolerate cold as well as others.
"Dogs evolved from wolves, and so they still have some of that ancestry remaining. But that doesn't mean that one should go and drag around in the snow the entire time. There are many varieties of dogs nowadays that are not able to stand cold due to breeding," Ninomiya said.
The findings are published in the journal Veterinary Dermatology.