Many breeds of dogs are used to pull sleds, including official American Kennel Club breeds such as the Siberian husky, malamute and Samoyed. However, many sled dogs are of mixed breed and are called Alaska husky or Eskimo dogs. While some sled dogs may have wolf bloodlines, it's generally not desirable to crossbreed sled dogs with wolves.
Sled dogs are bred for their speed and endurance as well as leadership qualities. They are big dogs with thick coats and wide, flat feet. They sleep with their tails covering their noses to keep warm. Dogs that weigh around 40 to 45 pounds (18 to 20 kg) are the ideal size to pull sleds, but some may weigh as much as 85 pounds (38.5 kg).
Young dogs that are enthusiastic runners, easygoing and mentally tough are good choices for sled dogs. A dog's gender matters little -- both male and female dogs are considered equally.
For racing, the most intelligent and fastest dogs are picked to be lead dogs and run in the front of the pack. Behind them run swing dogs, whose job is to direct the team around turns and curves. At the back of the dog team are the wheel dogs or wheelers, who are right in front of the sled and are usually the largest and strongest of the team. The rest of the dogs are known simply as team dogs.
Dogs are typically from 2 to 10 years old when they pull sleds. After they retire, they might remain with their owner at a kennel or be adopted as pets by others. Rescue groups for sled dogs take in unwanted dogs and care for them, trying to place them in loving homes.
While snowmobiles (also called snow machines), helicopters and airplanes are now often used in place of sled dogs, there are still times when canine transportation is preferred. Harsh weather conditions can make flying hazardous, and certain terrain can be more difficult for snow machines to cross than for dogs. Dogs can be more reliable than man-made machines, they're good companions to have on long treks and they can be cheaper to own than other forms of transportation.
In the next section, we'll find out how a dog becomes a sled dog and if most mushers treat their pack humanely.