We've had several Shepherds, all have been good with our other animals and our children.
They are first and foremost a tending dog, so their basic nature is to guard whatever they consider to belong to their "family."
They have been bred rather indiscrimitately by backyard breeders in the US, however, so be careful in your search.
They are prone to several genetically linked problems, including hip and elbow dysplasia, and tendencies towards pancreatitis and issues with enlarged esophagus. You should definately discuss these with any breeder you are considering, and if they can't provide good answers as to how they are keeping these problems from their line, or are dismissive of your questions, look elsewhere.
A good breeder will have an OFA (orthopedic foundation for animals) registration number confirming sound hips, at a minimum (not all breeders xray Shepherds for elbows) on the parentage of the litter. This is not a guarantee that your pup won't develop dysplasia, but you're far less likely to have issues than with a backyard breeder simply making a buck off whatever papered pups they can produce.
See:
http://www.offa.org/
... and verify your breeder's certification.
http://www.offa.org/search.html
You should expect to pay $500-$1500 for a good working line Shepherd, if that is what you are aiming for. That sounds expensive, but vet care for a dog with bad hips or pancreatitis will cost you far more, and seeing a young dog in the prime of life with a crippling ailment is heartbreaking. I went through that with my first Shepherd; I asked about OFA, and took a backyard breeder at his word instead of asking for the certificate number. Five years later, I and my beloved pet were at the vet, spending about $3000 on hip surgery, that was lucky for us) succesful ... the vet said my dog had the worst hip sockets he'd ever seen ... don't support Shepherd breeders who don't xray by buying their pups.
There also seems to be an American fixation with breeding bigger. A good German Shepherd Dog is within the breed standard, 24"-26" at the top of the shoulder for a male, 22"-24" for a female. Shepherds bred for larger size are a) often bred for size with no consideration for anything else, and b) far more prone to hip problems.
Ask a lot of questions regarding the temperment of your breeder's line. Some working line Shepherds are quite "sharp" in temperment compared to what you may be used to, and you definately don't want to accidently acquire that much agression! Some breeders breed working lines for herding/tending work, but many working line Shepherds are bred for protection/police/military work, and they are a handful to work with outside their intended setting. I have one (and trained for LE work), and you don't want to get one of those if you arent prepared to work with that temperment.
Also, most dogs are originally descended from the jackal line of the canine world, and are more indescriminately social. German Shepherd Dogs are of the wolf side of the canine world, and are much more pack-oriented; they'll show far different behavior to those they identify as being part of their pack than of outsiders, so consider who might be coming by, and just how suspicious a nature you want.
I have a number of friends who come over every weekend, and have for years. They don't knock, they just walk in and yell "hello!" ... Several walked in together, and one had brought his brother along for the first time. My LE-line GSD picked the one new fellow out of the group in about a second, and had him backed against the wall doing a "bark and hold" til I came over and said "friend." That Shepherd is out of a line bred for police work, and he's just wired that way and he is very confrontational with people he does not know ... which can be a pain in the ... anyway, my other Shepherds have not been that mistrusting of strangers, unless they are given reason to be ... so ask questions regarding the temperment of your breeder's line, and don't get a line bred for protection work unless you know what you are getting and why.
Individual dogs will of course vary, and training and evironment do matter a lot, but breeding does make a huge difference, so don't discount that!
As far as GSDs and chickens go, most tending breeds will take to guarding anything you turn over to them, though, as I mentioned, there's been so much indiscriminate backyard breeding of German Shepherds that it is hard to tell what you are getting unless you get one of a real "working line." Some of that hard-wired tendency towards tending is gone from much of the backyard breeder stock.
GSDs are smart, need human companionship, and a job to do. Any tending or herding breed that is intended to "work" will be a problem animal if left penned with nothing to do, and a bored GSD allowed to roam loose will not necessarily be protective of other people's animals, and can become quite predatory.
Also, in my experience, slow moving cars and bicycles tend to set off German Shepherd Dogs ... I don't know if it is the speed resembling that of a predator, or what, but if my GSDs see a cyclist on the other side of a tree line, and just see that motion through the trees, they are off like a shot. Good thing for sturdy fences ... cyclists passing by our place get more cardio than they set out for.
You'll want a fence too, if you have nearby traffic of any sort.
Sorry for the lengthy post; I dont know much about chickens and lurk here to learn, but Ill peep up and contribute where I do know a thing or two ... I've had GSDs for years, and have trained for LE and Schutzhund.
Good luck finding your next best buddy!
