The Alaskan sled dog has evolved over the past century from a working dog, originally developed to haul cargo sleds over snow-covered terrain to an elite modern-day athlete. Their dominating presence in polar exploration and the boom of the Alaskan Gold Rush gave rise to the "Era of the Sled Dog" from approximately the late 1800s to the early 1900s. The incorporation of modern transportation methods forced the sled dog into retirement from its necessary role of working dog, transitioning, instead, to a sport-racing dog. Though not recognized by the American Kennel Club (AKC) and not developed to meet a physical standard, Alaskan sled dogs are bred for climate-specific athletic performance attributes, which has resulted in a level of genetic distinctiveness comparable to that of AKC-recognized breeds. Performance selection has given these dogs a common athletic type: a quick and efficient gait, superior pulling strength, and increased endurance. Overall body weight and coat type, however, can vary depending upon racing style, geographic location, lineage, and cross breeding to purebred lines. Sled dog racing can be divided into two distinct styles based upon the mileage teams' travel. Long distance racing covers approximately 1,000 miles over multiple days with moderate racing speeds (13–19 km/h) (Iditarod and Yukon Quest), while sprint racing is comprised of multiple events or classes defined by the number of dogs in the team (4–20), faster racing speeds (29–40 km/H) and shorter distances (6–38 km). The extreme differences in racing style has led to divergent selection of Alaskan sled dogs for either endurance or speed, resulting in two distinct populations.
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The subset of breeds that had contributed most to the development of the sled dog includes the Alaskan Malamute and Siberian Husky. Interestingly, the Pointer, which has been repeatedly bred into the sprint dogs in recent years with the idea of enhancing speed was not found to positively affect speed performance. The Samoyed, Chow Chow, and Akita also have historical roots as northern draft dogs. Other breeds included in the "related breeds" group were the Saluki, Afghan Hound, and Borzoi, which are well known for their speed, the Great Pyrenees and the Anatolian Shepherd, both of whom are northern climate guard dogs, and the Weimaraner, a hunting breed of shared ancestral heritage to the Pointer. The Saluki and Anatolian Shepherd both had minor positive influences for exceptional speed performance in sprint and distance populations, respectively. Unexpectedly, the Anatolian Shepherd, whose heritage describes a large, powerful, and independent northern livestock guardian dog, demonstrated a 6% positive influence in distance sled dogs of high work ethic, a three-tiered system based on the dog's willingness to run. The effort a dog puts forth during a run is determined by the amount of tension a dog places on his individual tug-line. Dogs demonstrating the strongest effort, defined by having a constant tug-line tension throughout the run, are designated as rank 1 (top line). Rank 2 (middle line) define dogs that have intermittent tug-line tension throughout the run, but maintain the speed of the team. The poorest performers, rank 3 (bottom line), show no tug-line tension during the run but are capable of the speed and mileage.
Breed-Specific Ancestry Studies and Genome-Wide Association Analysis Highlight an Association Between the MYH9 Gene and Heat Tolerance in Alaskan Sprint Racing Sled Dogs
- A genetic dissection of breed composition and performance enhancement in the Alaskan sled dog