From the BBC:
Dogs can keep warm on frozen ground, thanks to a specialised circulation system in their paws, say scientists.
Researchers in Japan used electron microscopes to study the internal structure of domestic dogs’ paws.
They found that heat was transferred from the artery to the network of veins, meaning that cooled blood could not return to the body.
The system has been recognised in many other animals’ extremities, including penguins’ beaks and dolphins’ fins.
The findings are published in the journal Veterinary Dermatology.
Arctic foxes and wolves are well known for their adaptations that help them to regulate a constant body temperature in cold conditions.
Previous studies showed that the canines can keep the tissue in their feet from freezing even in temperatures of -35C.
Dr Hiroyoshi Ninomiya and his team at the Yamazaki Gakuen University in Tokyo, Japan, set out to discover if this ability was also common to domestic dogs.
Using electron microscopes, the researchers were able to examine the internal structure of dogs’ paws.
They found that the very close proximity of the arteries to the veins in the footpad meant that heat was conducted from one blood vessel to another.
So when blood in the paw’s veins cooled on contact with the air or ground, warm blood pumping from the heart – through the neighbouring artery – transferred its heat.
The blood was therefore “warmed up” before it returned to the body – preventing the dog’s body from cooling down, whilst also keeping the paws at a constant temperature.
“It is well known that penguins in the Antarctic have a counter current heat exchange system in their wings and legs to prevent heat dissipation and keep the body warm,” said Dr Hiroyoshi Ninomiya.
“When we found that dogs also have such an excellent system in their paws, we were excited.”
Anatomist Dr Sarah Williams from the Royal Veterinary College says the evidence could be a revelation for dog experts.
“Up until now, it was not considered necessary for domestic species to posses such a specialisation.
“This discovery has interesting evolutionary implications, and may suggest that the ancestors of the domestic dog lived in cold climates [in order] to bring about such an adaptation.”
The ancestors of domestic dogs are wolves, and wolves do live in cold climates– which is where dogs got this trait.
However, dogs sweat through glands near their footpads. Northern wolves do not have these glands, and this is one trait that clearly separates northern wolves from domestic dogs. Eastern coyotes, which are part northern wolf, also have no sweat glands on their feet, while Western and Mexican coyotes have them.
I have not seen any studies on Middle Eastern and South Asian wolves that have examined their footpads to see if they have sweat glands, but if they do, this would be very good evidence that dogs derived from these subspecies.
These sweat glands in dogs and some coyotes could be a way of cooling the feet that initially evolved with this sophisticated warming mechanism to keep them from freezing in very cold climates.
This needs to be explored.
If Middle Eastern and South Asian wolves have these sweat glands, it is a definite smoking gun that clearly shows dogs have an affinity with these subspecies.
I guess dog feet were more interesting than we initially thought.
Thanks Scotty, this is actually something I’ve often wondered about.
Salukis and Greyhound types that are adapted to activity which produces a lot of heat (running) tend to have lower thyroid levels than other dogs. It would be interesting to know whether wolves in the ME also have it.