If you haven't seen any of my other posts - I'll recommend a German Shepherd. Here's Rex with his first batch of chicks in April:
And his third batch of chicks (just got yesterday)
Lots of other pictures of Rex and his flock on my personal pages. He must be doing a good job because we live in the country with every predator there is and so far nothing has gotten them. After we got the first baby chicks Rex began insisting on sleeping outside with them. They free range all day, usually in his presence, and our run is open with no cover and their coop is left open at night with Rex out there.
Like the posts have said - it depends on the dog more than the breed. If you get a breed like a GSD it has to have a JOB plus be well trained and socialized from birth. Dogs like this have lots of energy and must have an outlet so if you aren't prepared for lots of exercise, don't get a high energy dog of any breed. Rex plays ball, frisbie, and swims/retrieves to burn off energy. He'll run the equivalent of several miles catching balls that you can throw till your arm falls off and he won't quit - might run take a quick swim in pond and run back with ball but won't quit. He's responsible for guarding us and baby chicks and kittens and he gets the paper and brings in groceries. We didn't "train" him to watch the chicks - just worked with him a few minutes till he understood that they were loved and part of family. Dogs of this type have an innate sense of protection and duty.
Funny story: Rex loves to go the long distance down our drive to get the paper. If my husband gets it and doesn't give it to Rex to carry back, Rex gets upset. One day husband told Rex to go get the paper. Well Rex didn't go so my husband went. When Rex saw husband was going to get paper he ran down there but husband would not give it to him, told him "no, you wouldn't go get it so you don't get to carry it in and get a treat". Well, just to show you how smart they are: later, there was a paper on our door step; little while later another one; little while later another one; little while later yet another one - 4 in all. Guess he went all over the neighborhood stealing papers and brought 4 to make up for the 1 he wouldn't go get.