A sheepdog is a type of domestic dog whose original purpose was to herd or guard sheep. Sheep dogs are just one category of pastoral dogs. Man first trained sheep dogs to herd and guard his flocks thousands of years ago. This was a remarkable achievement, considering the fact that sheep would have been its natural prey. Man was able to mold them for the special task of tending sheep and to act on the sound of a whistle or by voice command for his advantage.