The idea is pretty simple, real life guardian dogs lived with the livestock and were used to guard them against predators, and herding dogs were used to control the herd. What I would like to see in Wurm is a simpler mix of the two, basically, a breed of dog (or any regular dog?) that once tamed could break up pile-ups of livestock on a tile. I.e. there is a large pen with many sheep in it and a tamed sheepdog, 3 sheep end up on the same tile, the dog walks to them and spreads them apart so they don't catch a disease.