A dog's coat keeps it cool: fact or fiction?
June 21, 2016 8:34 PM   Subscribe

I see a lot of lightweight articles of dubious scientific merit claiming that one should not shave down a dog's coat in the summer because it actually helps keep it cool during the summer. Can someone point me to actual science that upholds or refutes this claim?

Such articles often make what seems to me to be a poor analogy to a house's insulation, but it seems obvious to me that a house's insulation only helps a house stay cool in the summer because it is cooler inside the house than outside--either because you are creating "coolth" inside via air conditioning, or perhaps capturing coolth at night and then attempting to retain it during the day. Such articles may also state that of course a person doesn't wear a coat to stay cool, but that a dog's coat does not function like human clothing because it traps air as an insulator--which is exactly in the same way that human clothing insulates. I mean, it just seems patently silly--if heavy, double coats were good cooling systems then why is it that we see them in northern breeds, while dogs that have long adapted to hot, sunny climates typically have very short, single coats or even no coat at all? Why do dogs and many other animals grow heavier coats in the winter and then shed out substantially in the spring?
posted by drlith to Pets & Animals (12 answers total) 7 users marked this as a favorite
If the ambient air temp is higher than the dog's body temp, then the coat will keep the dog cool. Dogs don't sweat, so the situation is a little different from a human wearing a heavy clothes in the summer.
posted by ryanrs at 8:47 PM on June 21, 2016 [2 favorites]

Sunburn is also a major factor - dogs with heavy coats don't get tans. (I actually don't know if dogs tan at all, come to think of it.)

Dog body temp is higher than ours - around 102 degrees, so ryanrs's theory won't apply in many cases. We clipped our collie's belly and skirts pretty close for other reasons, but it did seem to reduce her heat stress somewhat. We left the exposed-to-sun parts natural, though.
posted by restless_nomad at 9:10 PM on June 21, 2016

My vet said the big concern is sunburn. So I get my collie-furred dog "puppy cuts" in the summer and anecdotally it seems to help.

If you ever see a dog park in the summer, though, it's clear the dogs with heavy fur get the hottest.
posted by lunasol at 9:26 PM on June 21, 2016 [2 favorites]

They have different fur though. I have a mongrel mutt who is like any tropical street dog - her fur is 99% all inch long silky hard strands that lie flat to her for a glossy coat. No fluff. I had as a child a miniature collie who had very distinctively a fluffy undercoat and longer guard hair that grew in over that as her visible coat. You could shave her down to her skin and she would be a ratty little thing and chilly for a while until the fluff grew back and she was happy in the heat, or clip her to her fluffy undercoat and she was happy. With the full coat, she was much more of a shade-seeker during hot days and at noon. Her fur up close had different textures - the short crimped undercoat of the fluff and the long thin pokey guard hairs of the top and the medium thickish coat fur.

So it really depends on the dog breed for the type of fur up close. Different fur structure will trap heat in different ways - density of fur, structure of the fur, length etc.
posted by dorothyisunderwood at 11:19 PM on June 21, 2016 [1 favorite]

And dogs do sweat - if your dog leaves wet paw prints and it's dry out and they're panting, they're sweating through their paw glands. Mine just did from a long hot run. We had a bottle of water during the run, a bottle before and a bottle after, but it was a sweaty run for everyone involved.
posted by dorothyisunderwood at 11:22 PM on June 21, 2016

Here's an article that addresses this, though not in great detail. According to an expert in comparative animal exercise physiology and thermoregulation at UC Davis, "Fur actually insulates the body in cold weather and helps prevent the body from taking on too much heat in warm weather," says Jones. "Fur acts as a thermal regulator to slow down the process of heat absorption."

The article then mentions sunburn and insect bites, and continues, "Dogs have developed their hair coats for a reason. It’s a barrier between the dog’s skin and the sun," according to Emily Rogell, medical director of the Metropolitan Emergency Animal Clinic in Rockville. "The less heat and sun reach the skin, the less hot the dog will be. I don’t recommend clipping or shaving unless there is a medical reason," such as a skin condition or terribly matted fur.

Shaving could also contribute to dehydration, says Jones, noting that research has found that “camels in the desert that are shaved, for example, do worse than those with fur, requiring more water evaporation to stay cool.”

It seems the consensus is that summer cuts are fine, but shaving is definitely not a good thing.

Speaking of water evaporation, though, one thing I've read that surprised me was that you should be careful with soaking a long-haired dog to provide heat relief because it could make things worse. I originally saw it elsewhere, but here's one mention of this: "On a related side note; if a dog does become overwhelmed by heatstroke, it is not advised to submerge the entire dog in water or pour ice-cold water over the dog as the different temperatures are too much to regulate quickly (use tepid or cool water). Additionally, long-haired dogs can become waterlogged causing the fur to hold in the heat and not let it escape. As you pour water over a dog, wipe off the excess with your hand, helping to remove the heat as well and not let the dog’s fur trap in the heat."
posted by taz at 2:16 AM on June 22, 2016 [6 favorites]

Here's a read as to why I don't shave/cut my Husky's fur...
posted by HuronBob at 3:47 AM on June 22, 2016

I think you're right to be skeptical of the "coat keeps a dog cool" idea, but it's surprisingly hard to find any science-based discussion of the idea online.

Here is one page I found that supports your thinking.

If the air around a dog is cooler than the dog's body temperature (which will usually be the case; a dog's internal body temperature is 101-102°F), then heat will be transferred by conduction from the dog to the air. Insulation around the dog will slow that transfer and make it harder for the dog to lose heat in this way. (While not interfering with the evaporative cooling from panting, which is a more important way for the dog to cool itself.)

But there's another way heat can be transferred - radiation. The dog may be hotter than the air, but its environment can still be heating it through radiation. The most radiation hits it when it's out in the sunlight. This page talks about the role of a dog's hair in slowing heating from radiation. Basically it's saying that radiation from the sun hits the hair and heats it up and then that heat is transferred through conduction to the skin. The longer the hair, the longer it takes for the heat to be conducted, so a dog with longer hair will take longer to heat up after the sun hits it. (The heating will still happen, though, so if the dog were outside for a long time the length of the hair might not end up being very important.)

We can also think about how much radiation the hair reflects or absorbs. It's the absorbed radiation that heats the dog. Darker colors absorb more radiation, so if a dog's skin were darker than its hair it should be helpful to leave enough hair to cover the dark skin well. But if a dog's hair were darker than its skin shaving it off and exposing the skin might reduce heating from radiation. (But would be a bad idea because the dog would get sunburned.)

But here's another factor discussed in my old animal physiology textbook: Radiation can penetrate deeper into a white coat than into a black one (because it keeps being reflected), so some of it ends up being reflected onto the skin. With a dark coat, since the part that heats up stays closer to the surface, it can be removed more quickly by wind. If the wind is blowing faster than about 6.7 mph, a black-haired animal will actually gain less heat from radiation than a white-haired one.

I think the bottom line is that the only way a dog's coat can help keep it cool is through slowing heating from radiation. How much it helps and how important that is might depend on factors like the dog's hair or skin color, how much time the dog spends in direct sunlight, or how windy the environment is.
posted by Redstart at 10:28 AM on June 22, 2016 [2 favorites]

Thanks for the very carefully thought-out answer, Redstart! Radiant heating has always been a bit of a mystery to me and I'll admit that physics is not my strong suit, but the idea that longer hair absorbs radiant heat at a distance from the skin rather than directly on the skin and therefore to some extent reduces radiant heat absorption does seem plausible (unlike "waterlogged fur traps heat" which seems like utter poppycock, no offense). I can even see a connection between that phenomenon and the fact that many animals show a wild type agouti color pattern where guard hairs are tipped black and lighter at the root, with a lighter colored undercoat if there is one.
posted by drlith at 7:24 PM on June 22, 2016

I agree, "waterlogged fur traps heat" makes no sense. Water is a better conductor of heat than air or fur, so waterlogged fur should allow faster heat transfer away from the dog. I wonder if what the article was trying to say was that steadily replacing the water next to the dog's skin with fresh, cold water will cool the dog faster than leaving the same water there after some heat has already been transferred to it.
posted by Redstart at 7:46 PM on June 22, 2016

I also don't think there's any validity to the idea that submerging a dog with heatstroke in cold water can make things worse. Here is an article explaining in detail why cold water immersion is the best treatment for human heatstroke victims.
posted by Redstart at 8:20 PM on June 22, 2016

I don't know - years ago a dog of mine chased a wild animal around a field in noon heat and came back in early heatstroke. Luckily our neighbour was a vet and she told us not to drench the dog (we'd put her in the shade already of course) with the hose but to empty out the fridge of frozen veggies and wrap them in tea towels for DIY ice packs that were laid against the dog's body to cool her down while we slowly dripped water into her mouth and encouraged her to drink until she could weakly lap up water on her own and eventually was cooled down and recovered. It took a few days for her to fully be back to herself again and they were never allowed out during peak sun again. These were shorthair dogs and there was abundant water around - puddles and marshy bits of water, the garden hose. But the dog didn't go near them, just staggered home panting desperately and shaking, and the vet neighbour only let us cool down the concrete floor with water from the hose, not the dog herself.

The thing I remember is that the dog was radiating heat like a kettle. The frozen peas melted fast, and we had to get more frozen food out to use as ice-packs. It was a hot day, but the dog was not just fur that had heated up some slight, but her body was generating intense heat.
posted by dorothyisunderwood at 1:08 AM on June 23, 2016

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