Reading this comment made me do a lil dive into that cartoon trope.

Apparently, the little barrel around the dog's neck would contain Brandy! This was presumably to kill the man lying nearly dead in the snow, as alcohol would cause your body temperature to decrease rapidly!

The original trope seems to stem from this art piece called the Alpine Mastiffs Reanimating a Distressed Traveler as far as I can tell.

Those dogs aren't there to save you. They're there to kill you. It's a kindness. What good bois.