How hot is too hot to run a dog?

There is no single temperature that is too hot. The veterinary literature can't agree on one. The things that decide it, humidity, ground temperature, cover, airflow, acclimation and the individual dog, don't reduce to a number. If someone hands you a hard cutoff, they're guessing.

Co-authored by P.J. Rose, NAVHDA judge, and Charles Ellithorpe, DVM, sporting dog veterinarian

Why there isn't a number

You would expect somebody to have published it by now. A temperature, a humidity reading, a line you don't cross. I went looking and couldn't find one that holds up, and neither could our resident veterinarian who reviewed this.

“Heat” isn't one variable. A dog sheds most of its heat by convection, air moving across the body, and by radiation, heat lost to the surroundings. Both start to fail as the air temperature closes on the dog's own body temperature, around 101 to 102.5 degrees. At that point panting has to carry the load, and panting cools by evaporation, which gets much less effective as the air gets more humid.

That's why seventy-eight degrees in dry air vs seventy-eight degrees in hot soupy air are two different days for a dog, and it's also why the thermometer on your truck can't tell them apart.

One anecdote worth taking away

There's a rule of thumb in circulation: add the air temperature in Fahrenheit to the relative humidity level, and if the sum exceeds 150, heat injury becomes considerably more likely. Eighty-five degrees at seventy percent humidity gives you 155. Eighty-five at forty gives you 125.

Treat it as a flag, not a limit. It's crude, its relationship to the human heat index isn't clear, and we can find it repeated in a lot of places without finding where it started. Charles calls that dogma: something repeated until it gets treated as fact. But it's a five-second calculation you can do in the truck.

What actually decides it

Read the day, then read the dog. No single factor is a stop sign. They stack, and the more of them present at once, the less margin the dog has.

The day

Humidity, the one people underemphasize, because it disables the mechanism the dog falls back on.
Ground temperature. Bare dirt, gravel, sand and cut stubble run far hotter than the air above them, and your dog is working in that layer.
Thick, wet cover, which holds water, blocks airflow and makes the dog work harder.
Airflow. A still day is harder than a breezy one, and a crate without moving air is harder still.
Time of year. Heat cases rise in spring and early summer, when temperatures climb fast. Additionally, the dog usually hasn't acclimated and his fitness is at its lowest. The first warm week is more dangerous than a hotter week in August.

The dog

Conditioning. An unfit dog makes the same heat with less capacity to shed it.
Drive. The dog that won't quit is often the one in trouble before you notice.
Any previous heat episode. Think of thermoregulation as a thermostat that can't be replaced. If it blows once, tolerance can be lowered for the rest of his life.
Coat, color, weight, age.

Conditioning, drive and history are easy to overlook, so pay special attention to these factors. An overweight dog, a dark coat and an old dog are things you can see plainly.

So what do you actually do?

Knowing when not to run is half of it. The other half is recognizing heat injury in the order it appears, and knowing what to do in the first five minutes which is where a lot of the advice still in circulation is out of date.

That's what our guide covers: the warning signs in a sequence you can track, what each one means for your dog, the current cooling protocol, and what to say on the phone to the clinic if it comes to that.

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