Wonder why your dog’s paws don’t freeze in the winter? Here’s the answer

The Problem

  • A dog’s paws are more exposed to the cold than the rest of their (fur-covered) bodies.
  • Dogs and other members of the dog family can spend long periods of time exposed to cold, snow and ice without hurting their paws (think dogs in the Iditarod, arctic foxes, my dog whenever it snows and she refuses to come inside because SNOW).
Photo Credit: Tiger Productions
Ohmygodweeeeesnowyaaaasss!! Photo Credit: Tiger Productions
  • Scientists have already shown that these animals can keep their paw temperature just above freezing even when they’re exposed to temps of -35 degrees Celsius (-31 F, or, my feet every night when I’m trying to fall asleep).
  • Scientists weren’t sure why their paws didn’t show signs of damage, since long-term exposure to cold causes damage in other animals.

The Study

original

  • Scientists took legs from previously euthanized dogs (science is NOT always glamorous or pretty, y’all) and injected some of the legs with a colored resin that hardened and dyed the veins and arteries red.
  • They injected the some of the legs with a mixture that dyed the veins and arteries black.
  • They cut the legs and paws into very thin slices to mount them on slides so they could look at them under a microscope.
Really really really close up picture (from a scanning electron microscope) of the veins and arteries in a dog's paw
Really really really close up picture (from a scanning electron microscope) of the veins and arteries in a dog’s paw. Photo Credit: Hiroyoshi Ninomiya, Emi Akiyama, Kanae Simazaki, Atsuko Oguri, Momoko Jitsumoto and Takaaki Fukuyama.
  • They studied the pictures of the specimens to find out how the vascular (veins and arteries) system of a dog paw works.

The Results

  • First, a quick anatomy review:
    • Veins– carry blood with very little oxygen left in it back to your heart. Blood that’s coming from the farthest parts of your body like your feet  (or a dog’s paw) is going to be cooler.
    • Arteries- carry mostly oxygen-full blood away from your heart to the rest of your body (I always remembered it as “Arteries = away”). Blood moving from the main part of your body to your feet (or a dog’s paw) is going to be warmer.
  • Researchers observed that dog paws have a type of heat-exchange system in them that looks like a little vein-artery-vein sandwich.
An artery "sanwiched" by two veins. Photo credit: Hiroyoshi Ninomiya, Emi Akiyama, Kanae Simazaki, Atsuko Oguri, Momoko Jitsumoto andTakaaki Fukuyama
An artery (a) “sandwiched” by veins (vp). Photo credit: Hiroyoshi Ninomiya, Emi Akiyama, Kanae Simazaki, Atsuko Oguri, Momoko Jitsumoto andTakaaki Fukuyama
  • This means that as a dog’s paw comes in contact with snow, warm blood in the arteries going out to the paw conducts heat to the cool blood in the veins coming from the paw (Think of putting your cold feet on someone’s warm feet- your feet get a little warmer and theirs get a little cooler. Am I the only evil person who does this??).
The heat exchange in a dog's paw looking down at it on a cold surface
The heat exchange in a dog’s paw looking down at it on a cold surface.
  • Researchers also found that the walls of the arteries in a dog’s paw are thinner. This makes it easier for heat to move from the arteries to the veins.
  • Dog paws have a distinct venous plexus (which is just a large number of veins bunched together in one place). This not only holds a lot of warm blood in one place to keep paws toasty but it also serves as a cushion to keep your pooch comfy.
  • Paws have a large number of anastaomoses. These are places where veins and arteries connect to exchange blood. These to dilate (get bigger, like your pupil) when the paw comes in contact with a cold surface. This means that warm blood can flow more quickly to the paws.

The Takeaway

  • The researchers learned a few important things that help explain why your dog does NOT need those booties to keep his paws warm (but don’t ever leave dogs out in the cold for extended periods of time- this could be really dangerous for them!).
  • The vein-artery-vein sandwich that exchanges heat in a dog’s paw cools the blood just enough so not a lot of heat is lost through the paws, but it also warms up the blood that has cooled down from touching a cold surface.
  • This helps maintain both the body temperature of the dog AND keeps the paw just warm enough not to freeze.
  • Unless they’re for protection from chemicals, sharp objects, or just for “fashion” (but really, no), the only dog booties we need to see this winter should be attached to wagging tails!
Maybe no one will recognize me with these shades on...
Maybe no one will recognize me in my booties with these shades on… Photo Credit: Breedfavorites.com

 

Question: Does your dog love to play in the snow? Would you ever make it wear booties?

Next question: Do you love snorting out loud? Do you love seeing dogs look ridiculous? If no, you are kind of a downer. If yes, watch this: https://www.youtube.com/watch?v=3tH785TVOjI

Read more on the (kind of gory) details of this study here:

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Author: Emily

I started Rise and Sci because I love science, I love teaching people new things and I want to help build a greater public understanding of all things science. My goal is to take hard to understand concepts and make them accessible to everyone- all in a fun an interesting format!

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