Kouya no Sakebigoe: Hoero Buck

Buck, a half German Shepard half Saint Bernard who's life is pretty peaceful and happy living with the Millers' in California. However, one day he is tricked and sold off. He ends up in the snowy North where he has become a sled dog during the Gold Rush. His story takes many twists and turns and he has to fight for his own survival.
(Source: Anime News Network)