All of this is relevant on the dog being worked also. I've had a couple of dogs that could and would work as hard in the summer as most dogs do in the winter due to their ability to suck wind better than any dogs I've ever seen. That is exactly why they were chosen to perform in the summer months. Whereas most dogs are blowing hot and just trying to push through, these couple of dogs never hit a heat wall or had an issue with the heat due to their ability to breath in such a way that it made no difference the temperature.