Thursday, June 22, 2017

Busting the Myth of Cooling Coats


 Figure 1. An infrared image of a Pembroke Welsh Corgi in the hot Arizona sun. Areas with thinner coat are noticeably warmer. Source: Doug Klassen, MyCorgi.com

When people see an infrared image of a dog in the heat (Figure 1), they tend to think the fur is keeping the dog cool because the fur appears colder than the surroundings. This is because the coat insulates the dog from the hot temperatures, trapping cool air against the body and slowing heat transfer to the skin (Figure 2). Unfortunately, this interpretation is incomplete and has caused widespread misconception about the role of fur in keeping cool.


Figure 2. Concept drawing of how fur insulates the dog from environmental heat.


Underneath all that fur is a dog that's trying hard to maintain a constant temperature. In order to maintain that temperature, the dog must release body heat to the environment. It does this in a number of ways (Figure 3). Note that insulation from outside heat is only a minor part of keeping the dog cool (compare Figures 2 and 3). Actual cooling effects, like air blowing through the coat (convection), panting (evaporation), or direct contact with cool surfaces (conduction) are much more important when maintaining normal body temperature in hot climates.


Figure 3. Concept drawing of the full heat environment of the dog. In order for the dog to maintain its core body temperature, metabolic and environmental heat gains must be equal to heat losses via convection, evaporation, and conduction.

Much like a thermos keeping a cup of coffee hot for hours, the fur inhibits these cooling mechanisms and greatly slows the rate of heat loss to the environment. This is great in cold temperatures but not good in hot ones. A thick fur coat may reduce the discomfort of stepping from a cool house into the hot summer sun, but over time a thick-coated dog is going to have more trouble staying cool than a thin-coated dog. A thick-coated dog can't release heat as easily as a thin-coated one.

With a better understanding of all the processes that affect the dog's body temperature, we can properly evaluate infrared images. In the infrared image showing a partially shaved dog (Figure 4), the skin is bright and hot not because the sun is beating down on it, but because the shaved part is radiating body heat much more easily than the furred part! The shaved area is actually significantly more effective at cooling the dog because there's no insulation to block body heat from escaping.

Figure 4. An infrared image showing the heat radiating from the coated and shaved parts of a dog. Source: unknown, Facebook.

The coat is important for a few reasons and the dog needs some insulation, so shaving to the skin is not necessary or recommended for summer comfort. That said, increasing air flow to the skin is necessary for efficient heat loss. Trimming hair to a reasonable length will go a long way in keeping the dog comfortable (aesthetic and coat health impacts notwithstanding). Without trimming the fur, the best way to help a thick-coated dog deal with the heat is to keep the fur well-brushed and as free from loose hair as possible.

This post was brought to you by basic thermodynamics. I apologize for the quality of the concept drawings; they were rescued from a failed hard drive and I haven't redone them.

10 comments:

  1. Hi Rachel! Love your posts and throwing in the engineering! I desperately need some advice though! I am in contact with a breeder that claims OFA testing has been done and will be able to produce certificates. However, she says she has not submitted these and will not be searchable online. From consulting your "Identifying a Reputable Breeder, v.3", you say "If the breeder says the tests were passed and they’re not listed on the website, you are being lied to." Would you say this breeder is untrustworthy then? Are there OFAs that are not submitted and unable to view online? Thank you!!! Your blog is a valuable resource.

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  2. you didn't mention the roles medullated hair, undercoats, and the seasonal shedding of undercoats play in regulating dog body temperature. i don't think you really have an understanding of dog physiology either.

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    1. Agreed. there is no scientific basis here or understanding of different types of coats or seasonal changes

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    2. WildSyph I agree this author is wrong on the role of the science behind a dogs cooling/ heat production

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    3. It would be helpful if you posted links to the claimed science. There is no reason to think that double coats that adapted to keep animals dry and warm in cold climates would then cool the dogs in hot climates.

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    4. Jeannette that is a great point. It does not make sense that a coat meant to keep dogs warm in cold weather would keep them cool in warm weather. It seems people are clutching to wives tales and negating any actual science done on this while being unable to produce to any scientific research themselves that would back up their claims.

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  3. She is just using physics to debunk the fallacy that an insulation keeps the dog cool, because it keeps the air around the dog cool.
    I think that the people who says that, should wear a coat in a hot place in the middle of the summer and hear that nonsense.
    On the other hand shedding on canids like foxes and wolfs are a natural way to regulate their body temperature, wolfs and foxes subespecies that are native to hot climates has a surprising VERY short hair on summertime, (or have large hairless areas to dissipate) And that doesnt happen on many dogs... you shouldnt forget that some breeds are artificially manipulated to have abnormally long hairs, and on top of that, are kept in hot places, thats far away from what we can call natural.

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    1. Absolutely correct. I can't believe the lack of common sense from those that swear you can't shave a dog with an undercoat. And somehow the design of the undercoat will keep a dog cooler than shaving it. Or those they prefer to torture their dogs in the heat because they think shaving will ruin the coat. I think the dog would rather be more comfortable on a hot day, than have concern over their appearance for their damn owners...

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  4. I love the idiots that hop on here and still somehow think and believe that a thick coat, with undercoat or whatever, is designed to keep a dog cooler than shaving it. Use a little common sense, or better yet, shave your damn dog in the summer and see the difference and quit torturing it...

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  5. Well, here is my $0.02. My opinion is not based in "science" but merely from observation. I have Pomeranians. If I shave them, they play, don't pant 24/7 and seem to enjoy life. If I don't shave them, they lay around, pant and seem very lethargic. Therefore, I shave my pups. I am more interested in their happiness than in vanity.

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