… and the answer is… maybe! It all depends on your dog. Read on for the evidence!
How do dogs lose heat?
Like everything else, dogs can only lose heat by 3 means (GCSE physics again anyone?):
- Conduction- through touching something colder, like a bed they’ve scraped in your best flower bed. I include evaporation in this as when the warmer moisture evaporates it leaves behind cooler moisture which cools the skin through conduction. Dogs don’t really sweat though.
- Convection- where heat is transferred into air (or water) and that air then rises carrying the heat away, being replaced by colder air
- Radiation- transfer of heat through electromagnetic waves through space. Unlike convection or conduction, where energy from gases, liquids, and solids is transferred by the molecules with or without their physical movement, radiation does not need any medium (molecules or atoms). Think of an electric hob glowing red- the red you see is radiation of heat.
Now we’ve got that cleared up, what’s a double coat? Dogs (in general) have two types of hair:
- Guard hair- strong, long, shiny. There to protect the undercoat. Can be erected by small muscles (arrector pili) to increase the effective thickness of the undercoat and improve insulation when cold but very little insulation in themselves.
- Undercoat- soft shorted curly hairs. Traps air against the body and provides insulation by restricting convection (air can’t move), conduction (skin can’t touch cooler surfaces) and radiation (each hair must radiate and transfer heat one to the other)
Different breeds have different proportions of these hairs- Yorkies have very few undercoat hairs and so look single coated.
So what’s the debate?
Essentially one side argues that clipping reduces this insulating layer and hence allows skin to lose heat more quickly. The other side argues that clipping reduces this insulating layer and hence allows skin to GAIN heat more quickly from a warm environment. Note this warmer environment usually means DIRECT exposure to the sun’s rays. The ambient temperature in the UK never goes above a dog’s core body temperature of 38.5C, so in the shade there is always a temperature gradient down from the skin into the environment.
In the absence of solar radiation, the temperature profile through the depth of the hair coat decreased non-linearly from the skin temperature to the hair-air interface. The temperature at the hair-air interface is higher than the air temperature
K. G. Gebremedhin – A model of sensible heat transfer across the boundary layer of animal hair coat (1986)
How do we resolve it? Let’s look at the evidence.
Evidence through common sense
OK, go sit in the sun topless. Now try with a T shirt. Now try with a thick fleece. Which was coolest? It’s the T shirt. It blocks solar radiation from heating the skin whilst allowing air to move and remove heat through convection. This is why people in hotter climates wear long flowing garments that protect the body from solar radiation whilst allowing air movement.
Now try the same experiment again in a sauna- now you’d be best off topless to allow maximum convection and conduction loss through sweat evaporation.
Evidence through evolution
Have a look at animals in cold and warm environments. Animals in cold environments have a thick warm layer of undercoat protected by guard hairs to stop it getting wet and dirty. Animals in warm environments have light coloured shiny guard hair dominated coats to reflect solar radiation whilst allowing some convection loss of heat. Without this protection from direct solar radiation animals will get solar dermatitis and ultimately skin cancer.
Coyote with thick woolly coat overlain with guard hairs
Clipping the coat short decreases its insulating abilities by 50% – “Predicted thermal responses of military working dog (MWD) to chemical, biological, radiological, nuclear (CBRN) protective kennel enclosure” by Larry G. Berglund, Ph.D.Miyo Yokota, Ph.D.William R. Santee, Ph.D.Thomas L. Endrusick, B.S.Adam W. Potter, B.A.MAJ Scott J. Goldman, V.M.D., Ph.D.Reed W. Hoyt, Ph.D.
The results simulated from this effort should be used as guidance material for safe stay times and procedures when implementing and sustaining MWDs [Military Working Dogs] in protective kennels. Based on these results, the battery powered ventilation fan should be used when possible in order to extend the safe stay times. Fur thickness of MWDs should be groomed to a length of 5mm on the back during warmer climate months to provide another increase in duration of safe stay time.
NB this is based on studies in kennels i.e. protected from solar radiation.
Often quoted to show that the long hair around the neck is cooler than the shaved body. This is correct but it does NOT mean the skin underneath the hair is cooler. The long hair is doing its job and insulating the skin underneath, which will be significantly warmer than 24C or 30.8C. And it’s the skin temperature is related to the core body temperature.
- In the absence of solar radiation, i.e. no direct sunlight, ALL breeds will benefit from a short coat. However this is a very unusual situation, and remember that clipping some dogs’ coats short may cause long lasting changes as it can take years for guard hairs to regrow in some breeds
- In the presence of solar radiation dogs need some protection from the sun’s UV, but we also need to improve heat loss through convection, conduction and radiation:
- Breeds dominated by guard hairs with little undercoat e.g. staffies, boxers- don’t clip, just groom out shed hairs.
- Breeds with a mix of guard hairs and undercoat- hand strip the undercoat , consider clipping the underside of the dog short
- Breeds predominately having a “wooly” undercoat e.g. poodle, golden retriever- clip to a length of 5-10mm to decrease the insulation layer, but keep some solar protection.
- Remember that dogs tend to lose heat effectively through panting, so dogs with short noses or respiratory difficulties can more easily suffer from overheating.
- Fat acts as an insulating layer, so overweight dogs will also find warmer environments more challenging.
- Dark hair absorbs heat more rapidly than light, but similarly radiates heat more rapidly