My family breeds german shepherds, they have been breeding them for around 13 years. We have a lot of them... Only whites and pandas. I train some of them, it is so easy to train them to not attack poultry, My girl Lupa never attacked them. She was bonded to me and I brought her out into the coop at 4 months and I did not attack the chickens so she did not. I have done some further work with her and she is excellent with all poultry and most birds now besides sandhill cranes. She is also trained not to chase deer which was pretty hard to do...
I think it is very important to train them not to chase deer because that has been the main cause of death for our dogs. Throughout the years we have had 18 dogs, 2 of them were hit by a car after they chased a deer through the streets. I also had trouble training my girl to not attack rabbits, she is fine with the ones in the hutch but the wild ones outside were so tempting to her when they would jump up and run. She could not see what it was and just saw that massive white tail bolting through the woods and she would chase after it and try to catch it to find out what it was.
Our most well trained dog was trained by my dad, he would attack almost nothing, I remember when I was young I would chase the chickens around and he would stop me. But he was not trained to be nice to cats and would try to kill them. If you want a german shepherd to be nice to animals you have to train it to be nice to all the animals you have around. If a GSD is trained not to attack chickens it does not mean he wont kill rabbits or sheep or cats. If you do not train your dog not to attack an animal then he will. If you do not train them to be nice to animals then, in my opinion, they will kill almost anything. They are not naturally nice to animals, no dog is.