It is my understanding that the cargo areas in the airplane are heated, and that animals are attended to between flights (i.e. not left out on the tarmac). You could call the airlines and inquire. My Pomeranian was flown to me in cargo. It seems the major issue in flying cargo is that in the summer months it can get too hot for some breeds (i.e. pugs) and the airlines will not fly them in cargo during hot months for this reason.