Gazette Vet: Summer Heat Is Tough on Dogs

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By John Andersen, DVM

I don’t have too many pet peeves, but one thing that really gets under my skin is when I see someone running with their dog on a hot summer day!

The scene is typical:

It’s the afternoon on a hot day—like 90 degrees. Getting a chunk of free time after work, the human prepares to head out for a run, excited for the prospect of some exercise and fresh air, despite the heat. The runner puts on the least amount of clothes possible—tank top, shorts, low-cut socks—and is ready to head out for a run through her neighborhood.

Staring at the runner as she ties up her shoes is the faithful dog, whom the human loves dearly. The human feels guilty—life is busy and walks are not as frequent as they used to be.  Here in the air-conditioning, the energetic dog grabs the leash and runs to the door, bouncing off the walls like a hyped-up child.

“It’s a bit warm outside” the runner thinks, but the energy of the dog and the guilt of the runner helps make the decision. “Let’s go, girl!” says the runner, and the dog barks with joy.

The dog, meanwhile, wears a thick, double-layer fur coat. The undercoat is dense with a remarkable “R-value,” providing fantastic insulation—keeping cold out and keeping heat IN.  On top of this lies the longer outer layer of the fur coat, adding even more insulation.  In the 71-degree air-conditioned home, the dog has adapted to being comfortable, despite being way overdressed.

Unfortunately for the dog, there is a large perception gap once the runner and dog head outside. It is 90 degrees and humid, though there is a steady, 5-mph breeze.

The runner quickly starts sweating and as the breeze hits the exposed, wet skin, evaporative cooling takes place.  “It’s not so hot outside,” contemplates the runner as she turns up the volume on her iPod and continues on.

The dog, on the other hand, instantly feels overwhelmed by the heat. Dogs do not sweat, so the nice breeze has absolutely zero effect on the dog’s core temperature. Further, as the muscle activity quickly starts to raise the dog’s body temperature, the thick fur coat does not allow for much of that heat to escape. The dog’s only method of self-cooling is panting, which by nature is fairly inefficient. Hot air is breathed out, cooler air is inhaled.  But when the air is 90 degrees with 90 percent humidity, this system doesn’t work very well. This is why wolves out in Yellowstone are not very active in the middle of the day in July—because it’s hot outside!

And contrary to what some people may think, there is no “keeping the heat out” property that the fur coat has. Maybe that would work in the 120-degree heat of Death Valley, California? But here, no, it’s just like you or I going for a run wearing an expensive thick fur coat–or a heavy puffy jacket and hat!

But the dog IS a bored dog, and IS excited to be with the owner, the runner. The heat that steadily is building up is nothing compared to the excitement of being out with the owner, exploring their vast territory. After a few minutes, the dog’s temperature raises to 102 degrees.

But after a mile, the heat is becoming intense. Despite a slow pace, the dog is becoming very hot. She starts lagging behind. Drivers from the road see a runner with a dog about 3 feet behind her, having to give an occasional pull on the leash.

The dog is now panting as heavy as possible, but is only getting hotter. Her vision is getting narrow, and she is getting a little dizzy. But dogs are tough—they don’t panic, she trusts her owner so she stays the course.

Finally, the owner takes a turn that brings them close to familiar territory.  The dog would be more excited if she wasn’t so near collapsing. The only thing she can think is “just stay with master.” Her instincts are doing their best to keep her from collapsing and leaving her only pack, her human. Her body temperature is now 105 degrees.

After 30 minutes of intense suffering, suffering that the human will likely only encounter a few times in her life, they make it inside the house. The dog nearly collapses by the water bowl, drinking water feverishly as she tries to cool down.

She then lies on the cool tile of the kitchen, panting heavily, but still way overheated. She is dizzy, feeling nauseated, and not seeing well. The owner refills the water bowl and goes to take a cool shower.

After about 45 minutes, the dog’s body temperature finally gets below 101 degrees. She is still nauseated. She goes to sleep exhausted.

The owner wakes her an hour later to offer dinner. Though she is not very interested, she does eat it, knowing this is mealtime, and another meal is not guaranteed. She eats and drinks, and lies back down.

“I really tired you out!” says the owner, “we need to go running more often!”

The next morning, the dog wakes up nauseas and vomits. On the morning walk, she has multiple episodes of diarrhea and doesn’t want to eat. The heat stress has really affected her body and it will take a couple of days before she is back to normal again.

Unfortunately, this is a pretty true story, happening every hot day of the summer. Some dogs are not as lucky as the dog above. Some dogs go into full heat stroke and die, their body temperature having reached, and stayed at, a critical level for too long. But for every case of heat stroke I see, there are likely 1,000 cases like this—heat stress, heat exhaustion—the name is not important, except to realize that the heat has injured them.

My summer tip is to respect the heat. If it is over 72 degrees outside, stop and consider what you are going to do with your dog. In my opinion, even 75 degrees is too hot to go running or go to the park for some fetch. Get up early in the morning, or go to places with water that the dog can soak/swim in to cool down. But mostly, just realize that summer is definitely the “off season” for dog activity. It’s okay to let them be lazy and enjoy the “dog days of summer”!

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