As for dog having to be introduced to the herd as a puppy so they think the herd is their pack:
I've found this unnecessary. I do believe that if you do this, there is no training needed as they do grow up naturally protecting their pack. BUT I had a Rottweiler that was born into a pack of 9 adult dogs. I then moved to Haiti with this dog and became a farm manager there. The goat herd was in most need of protection. I wasn't going to try to train my dog to protect the animals because I had heard they needed to be raised with the animals they were to protect. But I did want her to help me herd and not want to kill the goats. Well, through AI we had 33 kids all at once. My dog, fixed and never had puppies, assumed each kid as her own pup. She cleaned them, followed them around, protected them. It took some time, but she eventually started protecting the adults as well. She also helped nurture the orphans we had. There were many stages to this development but that's the gist.
We have had both with no luck. We live in a high predator area and have lost numerous goats and chickens to them. We have had a Pyrenees and a Llama. The dog was great if we were home, but come to find out if we weren't home he was off dragging dead deer home for snacks. They like to run. The Llama never attached to anything at our place she stayed in the furthest corner she could away from the goats and chickens and they appeared to dislike each other. That did not end well either a predator got her. We just lock everyone down at night and that seems to work out best.
I don't know if llamas would look after chickens.
I have 2 llamas that graze with my goats, though we hear coyotes pretty much all year, I have never had a problem with them on my property.
I have watched the llamas run from the back of the property all the way to the gate near the house to watch a dog and it's owners walking down the road past the house and stay there till they were out of sight.
Also in the pasture are several geese and a few chickens, when these have been taken by predictors such as raccoons, the llamas have done nothing to stop it.