Over the years that I've been involved with sled dogs, I have worked for, lived with and/or trained with numerous Iditarod and Yukon Quest veteran mushers which keep literally hundreds of dogs. These dogs are neglected in the name of sport and competitiveness, and it is often thought that treating them humanely "softens" them too much for racing (which is untrue). I have witnessed numerous atrocities, including: puppies being beaten with a plastic bat while in harness, sled dogs being killed and skinned for fur garments, dogs requiring major medical care being left to suffer and many other acts of cruelty and neglect.
The Sled Dog Action Coalition - a volunteer group committed to improving the lives of Iditarod sled dogs and providing truthful information about their treatment - has been kind enough to share some of the atrocities I have witnessed on their website, to help educate the public about the true realities these dogs face (link).
Please keep in mind that it is not only Iditarod and Quest racing dogs that suffer from neglect. Many sled dogs, from both racing and recreational kennels, are forced to live on short chains for the majority of their lives. These dogs often develop neurotic behaviors such as chain chewing, excessive digging, constant pacing, excessive barking and destruction of their house or anything else within reach.
The Journal of Veterinary Internal Medicine investigated the prevalence of gastric disease in racing sled dogs during the 2000 and 2001 Iditarods. 35% of the dogs tested during the 2000 race, and 48.5% of the dogs tested during the 2001 race had ulceration, erosion, gastric hemorrhage, or some combination of these findings. Results show that Iditarod sled dogs have a significantly higher prevalence of gastric lesions when compared to other dogs. (source)
In July 2002, the American Journal of Respiratory and Critical Care Medicine detailed a study of airway-passage disease in dogs who had recently completed the Iditarod. 81% of the dogs studied had abnormal accumulations of mucus or debris in their bronchial tubes that resulted in injury and inflammation. (source)
The Journal of Veterinary Internal Medicine published an assessment in 2005, showing that 61% of the sled dogs studied exhibited an increased frequency of gastric erosions or ulcers after completing the Iditarod, compared to 0% prior to the race. (source)
The Association of Veterinarians for Animal Rights states: "Arctic breeds of dogs are also routinely used for sled racing, which is another form of human entertainment and competition which subjects dogs to injury and death. When forced to run hundreds of miles a day, dogs sustain numerous injuries and illnesses, such as bone fractures, lacerated paws, ruptured tendons, torn muscles, cardiac failure, joint trauma, dehydration, stress and diarrhea. Injuries have also occurred when dogs have become tangled or strangled in the traces or harnesses. On average, 50 percent of dogs who start the Iditarod race, for example, break down and are unable to finish. As with greyhound racing, dogs who are bred for sled racing also are culled at a young age, or must undergo grueling training methods, and often spend their lives tethered on short chains."