No matter what, it depends on the dog's personality and your training him/her. I have 3 little dogs...Bichon Frise-10 lbs, a Yorkie/Bichon-15 lbs, and a Yorkie/Jug (Pug x Jack Russel)-9lbs...the Bichon wants to
mother the chickens (I swear), the Yorkie/Bichon stares at them with one paw lifted (bird dog style), and the Yorkie/Jug chases them but only when they are out of the pen. Most of the time my dogs just want to eat chicken poo!
The Yorkie/Jug stops when I tell her to, and has never laid a paw or mouth on any of the chickens, not even the 1 month old chicks that got out. She is a huge help in wrangling them back up to put back in the pen.
Because you want a small dog, you will need to train it so that it won't get hurt. (Any dog needs training.) My roos secure the perimeters when my dogs come out...only once have I seen hackles go up. The roos are doing their job if the dogs decided to "attack". My dogs would get their butts whooped (by the chickens) if they went after one. I have trained my dogs to "leave them" with a sharp voice, so they know the chickens are off limits. For some reason "leave it" doesn't work for the poo!
They eat it when I've got my back turned.
Good luck on your search for a dog.