Newchickenowner,
I am an experienced shock collar trainer, I have used it and have not used it, it depends on the dogs temperment that determines the best training route. Its generally used for very strong willed dogs, once that prey drive is triggered will not listen that is how my dog was. I have trained dogs that food was the best motivator, some not.
I have used it on myself when I first got it. It really doens't hurt them it gets their attention and that is what you are trying to accomplish, get the attention then correct the behavior. What happens with dogs is the prey drive kicks in and there is nothing that will stop them. This is a tool that really will get the attention of the dog, then you say "leave it" or whatever cue you decide to use.
My best advice when you use it is to make sure the correction takes place at the right time. Dogs live in the present, as I am sure you know that. If you don't correct that behavior within seconds of the unwanted behavior you will do more harm than good. Before you introduce the chickens to the dogs with the collar practice on something the dog really likes, a treat, a toy. Put the treat/toy out in front of the dog and when he goes for it, say "leave it" or whatever cue you decide to use. If they dont respond to the cue then shock, say "Leave it" and keep practicing the cue. They need to first realize the cue means stop, pay attention to mom. As you cannot always have the collar on the dog so best to learn a cue to teach them to pay attention.
I have a pit bull/boxer mix who behaves just the same off leash as he does on. It has taken alot of training but he is great with the chickens but it all comes down to who is the pack leader. You need to make sure those dogs understand who the leader is and when you speak they listen. What you are trying to accomplish with the shock collar is two things to associate the unwanted behavior with the shock but also a tool to get their attention to you. My dog knows the word "uh uh" is the cue to stop whatever he is doing and look to me. So no matter what he is doing, chasing a rabbit, squirrel, I say the word he listens and stops. He has a very high prey drive so I know about chasing things but it is possible and there is hope to teach the dogs to leave the chickens alone.
My dog goes in with the chickens with me, we do chores together and he walks around with the chickens with my supervision as again I never trust any dog with the chickens always supervised is the best advice. I have never used the shock collar yet in regards to the chickens. Its something I used for him the first few years of his life to learn behaviors I wanted him to learn,correct unwanted behaviors. Now I rarely need to use it because he knows who is the boss and its me, not him.
You have to on a daily basis show the dogs you are the pack leader not them. Be consistent is so important. They do not run the show, if you can do that and use the collar correctly it can work.
This is the best advice I can give you. Sorry this is long and wordy but I dont want you to be discouraged. I hope it works out for you. Any dog can be rehabilitated so there is always hope but it takes alot of hard work and consistency.