You've gotten some good advice already.
GSD are wonderful dogs. Very smart. They can hold grudges, so train just as smart. Therefore, be sure you are clear and consistent with your commands. Inconsistency is very annoying and builds disrespect for a GSD.
I would recommend letting your pup gain maturity first before working too much around or with the chickens. It will help it build confidence and respect (for you and later the birds). How soon chicken work begins depends on the dog, but basic obedience and a good leave it command are necessities before chicken work begins.
GSD need something to do and need mental stimulation. There is no such thing as a bored GSD...but they may find something you don't want them to do. ALWAYS keep them occupied with constructive things during their active puppy hood or things you want them to do. Never allow destructive behavior, not even once. They learn by opportunity and one time can be enough to set that behavior if it offered sufficient stimulus reward. Never let them have the opportunity to be destructive as retraining is much, much harder than training right the first time (and remember that grudge thing?).
As to training positive vs. negative reinforcements, really depends on your particular GSD. Some can be more stubborn, others softer. But they are SMART, so respect that. Back to clear consistent commands.
Generally, we found positive rewards balanced with negative consequences very effective with GSD. In our Guide Dog for the Blind puppy raising program, several projects with GSD, we used food treats and praise (rewards for good behavior) and then quick leash corrections (snapped like the "leash monster" bit...quick downward snap like a towel with leash using a chain training collar set so it relaxes the moment you release the leash) to get their attention if they are overly focused and lunging for something. The moment they look back at you, and they will as you have built relationship with them and they smartly want to please their person, praise, praise, praise. You are always warm and friendly when they look away from the offending object or stop the offending behavior. Use a 3 second rule. Either reward or punish within that window, otherwise, it is pointless. You will be reinforcing something you aren't meaning to address or encourage.
Taking them into overly stimulating situations too soon can "sour" the dog and create situations for failure for the dog.
Lots of basic leash work first then, with lots of controlled positive interaction as a pup and lots of interactive games that make them think to work off excess energy. Build trust. Focus energy. Train with positive/negative balance for obedience and impulse control.
Once they have worked through the appropriate basic level stage (how long depends on the dog), then you can begin higher stimulus situations...but always introduced slowly with you in control at the other end of the leash or drag line and a pouch of tasty food treats. Some GSD are environmentally sensitive and need to think through the new situation. Allow them the time to do so in a positive way.
My thoughts.
LofMc
Former Guide Dog for the Blind puppy raiser (7 projects...2 with GSD)
