Overheating

https://www.patriciamcconnell.com/theotherendoftheleash/overheating-in-dogs-the-concerns-increase

First, it probably goes without saying, (and yet I feel obliged to), that high internal temperatures in dogs can be a serious health emergency that can lead to organ failure and death. You no doubt know that a dog’s internal temperature is usually somewhere around 100 to 102.5, and that dogs are unable to sweat except through their paws. (Which has always confused me. Horses sweat and have coats similar to those of dogs; why can’t dogs sweat?) An internal temperature over 106 is considered a crisis; imagine my shock when I took Skip’s temp after a training run and it was, yeah, 106. (I should mention, however, that I used a digital thermometer, CiiNii, inserted in his ear, which I’m told is not as accurate as a rectal one.) Skip seemed fine after he cooled down, but needless to say, I take all this very, very seriously, and am now always quitting before I think I need to.

Dog Overheating: A Veterinarian’s life saving tips and what to do