I don't know about dog breeds, but in pre-Columbian Mexico/Central America, dogs were used as the primary source of meat and the primary "beast of burden", although it wasn't an especially good one. Dogs were the best the Aztec had when it came to animals carrying trade goods across long distances, so they were important and useful, but not as instrumental as, say, llamas in South America or horses and camels in Europe and the Middle East.