The dogs are to keep any stray sheep from escaping. Before that, they used behavioral methods on the sheep. If a lamb wandered off, the shepherd broke the lam

The dogs are to keep any stray sheep from escaping. Before that, they used behavioral methods on the sheep. If a lamb wandered off, the shepherd broke the lamb's legs and then carried it around until it healed. I think the sheep probably prefer getting herded to getting their legs broken. They probably also prefer it to getting eaten by a coyote, a not uncommon fate of lost sheep.