That isn't actually breathing. That is the dog's cooling system kicking in. Dogs don't sweat so they regulate their heat by breathing in cool air.

It's my uneducated opinion that this dog is working too hard during it's exercise and is having issues cooling off. She is "Overheating."

Dogs will reduce their speed or just lay down before they overheat. They are smarter than us in that respect. My dogs sometimes will just stand breath fast for a while, somewhat like in the video, get some water, then start again. Although after they go in cold water or use the hose water to cool down. Funny seeing one dog chase another with a hose.

Christ it annoys me that stupid people own animals.

Then again more stupid people have kids.. that makes me mad too.

WHY YOU HAVE DEPENDENTS STUPID PEOPLE ?

Sounds like a car that is ready to break down.

because they are stupid.

Break down? It sounds like the engine won't even turn over, all the way through I kept wanting to tell someone to stop, I think you've flooded it.