Why did perrault particularly need the best sled dogs for his job?

Perrault needed the best sled dogs in "The Call of the Wild" because he was a mail driver for the Canadian government. At that time in history the only way to get supplies and medicines to certain mining towns and other small villages was by sled dog. The dogs needed to be strong, smart, sound and have great stamina to keep going day after day in sub-zero temperatures.