You can't tell at a young age, you can't even tell when they are a year old, what kind of dogs they will be. Puppies don't just happen for the Nolkes. Sled dogs are bred to go faster and farther. You look at the traits and the lineage. Everything is pretty well documented.
Sled dogs are mostly huskies mixed with other breeds.
Hound dogs are coming back, it's a revival. German shorthairs and pointers are also breeds being used. But using scientific breeding methods doesn't always produce a winner. Even if a dog isn't cut out for mushing, the Nolkes tend to keep it around. The couple said they will probably find Bobeck a good home, but neither one seems in any great hurry to see him leave.