Ten checkpoints and four dog drops, some more than apart, lie along the trail. Veterinarians are present at each to ensure the health and welfare of the dogs, give advice, and provide veterinary care for dropped dogs; together with the race marshal or a race judge, they may remove a dog or team from the race for medical or other reasons. There are only nine checkpoints for rest, versus 22 in the Iditarod. Mushers are permitted to leave dogs at checkpoints and dog drops, but not to replace them. Sleds may not be replaced (without penalty) and mushers cannot accept help from non-racers except at Dawson City, the halfway mark.